plating through hole

Plating Through Hole

Trouble Shooting Guide Quality Requirements for Desmear (DS) and Plating Through Holes (PTH)

Electroless Copper (cPTH) & Driect Plating (DP) Horizontal & Vertical Application

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PTH Trouble Shooting Guide V2.0

BTT-PTH · Electronics Division Atotech Deutschland GmbH · Berlin · Germany

Validity and ApprovalsChanges Record

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Validity and Approvals

Please note that this is the official and only version of the PTH Trouble Shooting Guide. This version is valid from it’s signed release until the release of a later version signed as the official version. This file is: PTH_tsg_v02.doc; Version 2.0 Berlin, 30. January 2004

Dr. Gerd Linka

Business Manager BTT-PTH Electronics / BTT-PTH BM

Hans Joachim Grapentin Manager Training & Documentation

Electronics / BTT-PTH Tech-Doc

Dr. Lutz Stamp Manager Research & Development

Electronics / BTT-PTH R&D All recommendations and suggestions appearing in these instructions concerning the use of our products are based upon tests and data believed to be reliable. However, as the actual use of our products by others is beyond our control, no guarantee, expressed or implied, is made as to the effects of such use, or the results to be obtained whether the use of our products is made in accordance with recommendations or suggestions contained in these instructions or otherwise. Furthermore, information on the use of our products is not to be construed as a recommendation to use such products in the infringement of any patent. © Copyright - 2004 Atotech Deutschland GmbH Printed in Germany · All rights, including technical changes, reserved. This document may not, in whole or in part, be copied, photocopied, reproduced, translated into other languages or passed on to third parties without the prior written consent of Atotech BTT-PTH Tech-Doc Department.

Atotech Deutschland GmbH BTT-PTH Tech-Doc Erasmusstr. 20 D-10553 Berlin · Germany

Changes Record

Revision Date Changes Initiated by

2.0 30.01.2004 Review, new layout L.Maier / BTT-PTH

1.2 07.062002 Review L.Maier / BTT-PTH

1.1 17.12.2001 Release L.Maier / BTT-PTH

0.0 10.08.2001 Compilation Provisional Trouble Shooting Guide L.Maier / BTT-PTH

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BTT-PTH · Electronics Division Atotech Deutschland GmbH · Berlin · Germany Content

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Content Validity and Approvals...................................................................................................................................................................2 Changes Record.............................................................................................................................................................................2 Content ............................................................................................................................................................................................3 Preface.............................................................................................................................................................................................4 Definitions .......................................................................................................................................................................................4 1. Voiding (Plating Through Hole Defects) After Plating Through Hole (PTH) including Blind Microvias (BMV) ........5 1.1 No Coverage at all (or Partial) ..........................................................................................................................................6 1.2 Voids on Resin Only..........................................................................................................................................................8 1.3 Voids on Glass Fibers only – Glass Voids (classical PTH) .........................................................................................10 1.4 Voids on Glass Fibers only – Glass Voids (Neopact) ..................................................................................................11 1.5 Voids on Glass and Resin (Compact CP)......................................................................................................................12 1.6 Voids on Glass and Resin (Seleo CP)............................................................................................................................13 1.7 Ring Voids / Wedge Voids ..............................................................................................................................................14 1.8 Voiding Mechanism.........................................................................................................................................................21

1.8.1 PTH-Void: LB, Strike/Pattern Plate, Metal Resist ...................................................................................................22 1.8.2 PTH-Void: LB, Strike/Panel Plate, Metal Resist ......................................................................................................23 1.8.3 PTH-Void: LB, Strike/Panel Plate, Tenting..............................................................................................................24 1.8.4 PTH-Void: LB, Panel Plate, Tenting .........................................................................................................................25 1.8.5 PTH-Void: HB, Pattern Plate, Metal Resist..............................................................................................................26 1.8.6 Photo Resist Residue Void: LB, Strike/Pattern Plate, Metal Resist .....................................................................27 1.8.7 Photo Resist Residue Void: LB, Panel Plate, Metal Resist ...................................................................................28 1.8.8 Photo Resist Residue Void: HB, Pattern Plate, Metal Resist ................................................................................29 1.8.9 Metal Resist Void (Gas Bubble): LB, Strike/Pattern Plate .....................................................................................30 1.8.10 Metal Resist Void (Gas Bubble): LB, Panel Plate ...................................................................................................31 1.8.11 Metal Resist Void (Gas Bubble): HB, Pattern Plate................................................................................................32 1.8.12 Direct Plating Voids: DP, Strike/Pattern Plating, Metal Resist..............................................................................33 1.8.13 Direct Plating Voids: DP, Panel Plating, Metal Resist ...........................................................................................34 1.8.14 Direct Plating Voids: DP, Pattern Plating, Metal Resist.........................................................................................35 1.8.15 Gas Bubble in Acid Copper: LB, Strike/Pattern Plating, Metal Resist .................................................................36 1.8.16 Gas Bubble in Acid Copper: LB, Panel Plating, Metal Resist ...............................................................................37 1.8.17 Gas Bubble in Acid Copper: HB, Pattern Plating, Metal Resist ............................................................................38 1.8.18 Direct Plating: Gas Bubbles .....................................................................................................................................39 1.8.19 Poor Tenting: LB, Strike/Pattern Plating.................................................................................................................40

1.9 BMV or HARP Coverage Problems ................................................................................................................................41 1.10 Barrel Cracks due Stress in Plated Copper after Thermal Treatment ........................................................................43 2. Pull-away: Adhesion Problems on Resin prior Thermal Treatment ...........................................................................44 3. Resin Recession – Adhesion Problems on Resin after Thermal Treatment..............................................................46 4. Wicking – Copper Re-Plating..........................................................................................................................................48 5. Blistering and D-Effect – Adhesion Problems on Copper Surfaces...........................................................................50 6.1 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Prior and After Thermal Treatment ..........................52

6.1.1 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Rest Smear...........................................................54 6.1.2 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Poor Copper Crystal Structure .........................55 6.1.3 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Burning at Innerlayer Interface .........................56 6.1.4 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Corner Cracks.....................................................57

6.2 Foil/Copper Clad Cracks – After Thermal Treatment ...................................................................................................58 7.1 Pocket Voids – After Thermal Treatment ......................................................................................................................59 7.2 Delamination – Before and After Thermal Treatment ..................................................................................................61 8.1 Negative Etch Back– Copper Innerlayer Recession ....................................................................................................62 8.2 (Positive) Etch Back– Excessive Etch Back of Dielectric Material .............................................................................64 9. Star Burst – After Electroless Copper Plating ..............................................................................................................65 10. Blow Holes – Outgassing after Thermal Treatment .....................................................................................................66 11. Pink Ring – (or Red Ring) on Black Oxide Layer..........................................................................................................68 11. Tooling Hole Problems– After Electroless Nickel/Gold Plating (ENIG)......................................................................70 Typical Phenomena in Cross Section of Plated Through Holes..............................................................................................71 Typical Phenomena in Cross Section of Plated Microvias ......................................................................................................72

Remark: Critical passages are marked with

Abbreviations: H: Horizontal Application (Uniplate ) V: Vertical Application (DynaPlus)

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PrefaceDefinitions)

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Preface During production, the quality is affected by a lot of parameters and influences. There are two different scenarios: The failure increases slowly over time or occurs “suddenly”. In the first situation, an event occurs due to an influence over time, which is mostly a systematic fault, e.g. filters blocking because of too many particles resulting from insufficient cleaning or aging. In the second case, something has changed. This could be a random fault e.g. operation mistake: temperature too low, the human factor or something fundamental has changed in production e.g. different pressing parameter or rework. In any way, troubleshooting tries to point out where the failure is coming from. Because of the number of influences it is necessary to exclude as many parameters as possible. Therefore, first of all it must be assured that no systematic failure is responsible for the failure. The process parameters must be within Atotech specification. Also operation conditions as well as production equipment (e.g. water, chemicals, machines) must be in range. It is impossible to start troubleshooting, if production is out of spec or some systematic parameter (e.g. water quality) influences production. It also has to be assured, the investigation and quality control is carried out correctly. Sometimes failures have occurred which are not production faults, but created due to insufficient preparation of the samples. Further, mistakes from analytical control can lead to serious problems as analysis can not determine some parameter variations. The main sources for trouble are: ⇒ Changing of product mix (out of specification) ⇒ Changing of board parameters (base materials, pressing, drilling, panel size) ⇒ Changing of water quality (faults in water processing, cycle water) ⇒ Changing of base chemical quality (new batch, cheap supplier, no quality control) ⇒ Insufficient know how of personnel (untrained workers) ⇒ Operation mistakes (untrained workers) ⇒ Mistakes in materials science and analytical laboratory (untrained workers) For the specifications of water and base chemicals, please refer to the corresponding process notes.

Definitions

IPC-T-50F In order to use the same language, all terms refer to IPC-T-50 revision F.

IPC-A-600F For qualification of the faults refer to IPC-A-600 revision F.

IPC-QE-605A More faults related to printed circuit board production are shown in IPC-QE-605 revision A.

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Voiding (PTH Defects)After PTH including Blind Microvias (BMV)

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1. Voiding (Plating Through Hole Defects) After Plating Through Hole (PTH) including Blind Microvias (BMV)

In General: The most important factor to make good coverage results possible is the Smear removal process (e.g. Securiganth P) prior to each PTH-process, which means : The hole surface must be uniformly clean, Hydrophilic, May be suitably rough and Smear must be removed from copper innerlayers.

For this background it is absolutely necessary to adjust the Desmear/cleaning process to the right conditions related to the base material used (refer to the Process Training Manuals Securiganth P). Long experience in trouble shooting has shown that most coverage problems (voiding) are not related to the PTH processes. Problems can be related to: ⇒ Poor quality of the base material, ⇒ Poor drilling, ⇒ Unsuitable or not efficient pre-cleaning (Desmear) process, ⇒ Incorrect PTH process for the base material used, or acid copper bath (too high

organic concentration), or related to the design of the printed circuit boards (PCB) i.e. blind microvia (BMV) or RCC1- or semi-additive process (SAP) SBU2-technologies incorporated into the board,

⇒ Resist residues prior to electrolytic panel plating, ⇒ Aggressive etch cleaner used in pattern plate technology and last but not least ⇒ Tin or tin/lead plating faults, which are used as etch resist.

Voiding There are different kinds of voiding i.e. : ⇒ No coverage at all (or partial coverage ), ⇒ Voids on resin only, ⇒ Voids on glass only, ⇒ Ring voids , ⇒ Wedge Voids (refer to pink ring) and ⇒ Blind Via (BV’s), Blind Microvia (BMV) or High Aspect Ratio Panel (HARP)

coverage problems.

⇒ 1 RCC - Resin Coated Copper (Clad) 2 SBU – Sequential Build-Up

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Voiding (PTH Defects)No Coverage at all (or Partial))

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1.1 No Coverage at all (or Partial)

Sources of Defects How to Avoid...

High aspect ratio of drill holes

⇒ If only small holes affected, check wetting. (V/H)

⇒ If all hole diameters are affected, check Desmear/PTH performance. (V/H)

Insufficient wetting ⇒ Install or check vibration. (V)

⇒ Check the floodbars performance (change to AFD floodbar system). (H)

⇒ Install Knocking Rollers if enhanced flooding do not solve wetting problems. (H)

Blocked holes ⇒ Board inspection after drilling. (V/H)

⇒ Check active baths and rinses for residues and particles (dull liquids). (V/H)

⇒ Check electroless/acid copper baths for particles formed by wrong process parameters (perform cleaning cycle). (V/H)

Poor or incorrect (too hot) drilling, especially for large holes

⇒ Check drilling parameters. (V/H)

⇒ Check for stronger Desmear (Sweller !) paramerters, which are able to attack the glazed resin at the hole surface, but take care about a too excessive Desmear result. (V/H)

Contaminations ⇒ Check the whole Desmear process .Two cycles may be used for a test, but the second pass without Sweller. (V/H)

⇒ Check reduction of manganese dioxide after desmear due to inhibition of the palladium activation. (V/H)

⇒ Check the rework program and make sure that the electroless copper is completely etched off. (V/H)

NOTE: It is senseless to focus on a PTH chemistry problem, when only one through-hole out of 10.000 through-holes is not plated ! In this case all sources of defects are not related to the PTH chemistry !

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Voiding (PTH Defects)No Coverage at all (or Partial))

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Ring Void 40x

Blocked Hole 100x

Blocked Hole

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Voiding (PTH Defects)Voids on Resin only

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1.2 Voids on Resin Only


Highly cured resin ⇒ Overheating at drilling can create a hydrophobic surface on resins, therefore check drilling parameters. (V/H)

⇒ High-Tg base materials need a special pre-cleaning using ultrasonic support in the alkaline permanganate-etch solution. (V/H)

⇒ Check ultrasonic device in Sweller. (H)

Manganese dioxide [MnO2] residues ⇒ Check reduction solution after the permanganate-etch. (V/H)

Contamination ⇒ Check the whole Desmear process .Two cycles may be used for a test, but the second pass without Sweller. (V/H)

⇒ Check the rework program and make sure that the electroless copper is completely etched off. (V/H)

NOTE: For these defects, the PTH chemistry is not really responsible !

No Coverage on Resin 309x No Coverage on Resin 711x

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Voiding (PTH Defects)Voids on Resin only

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Voids on Resin 56x

Voids on Resin 230x

Voids on Resin 500x

Voids on Resin 150x

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Voiding (PTH Defects)Voids on Glass Fibers only (cPTH)

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1.3 Voids on Glass Fibers only – Glass Voids (classical PTH)


Poor glass surface cleaning ⇒ Check Desmear process, mainly the reduction step for performance. (V/H)

⇒ For glass cleaning, Securiganth P Glass Etch Additive or Securiganth FluorEtch AC may be added but not in combination with the direct plating process Neopact. (V/H)

Poor conditioning ⇒ Check reduction step after the permanganate-etch for performance, which creates the highest effect on glass conditioning during MnO2 dissolution. Only the reduction solutions (Securiganth Series) do not contain a conditioner component. (V/H)

⇒ Check the conditioner in the PTH line for performance (refer to corresponding data sheet). (V/H)

Poor activation / reduction ⇒ Check activator visually, the concentration of palladium, pH and temperature. (V/H)

⇒ Check the reducer for performance (refer to the corresponding data sheet). (V/H)

Poor quality of electroless copper deposition

⇒ Activity of the electroless copper bath may be too low. For this reason check all bath parameters and compare with the recommendations of the corresponding data sheet.(V/H)

NOTE: In any case, check the filter cartridges (filter must be free of passivation/ impregnation agents) !

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Voiding (PTH Defects)Voids on Glass Fibers only (Neopact)

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1.4 Voids on Glass Fibers only – Glass Voids (Neopact)


Poor glass surface cleaning ⇒ Check Desmear process for performance. (V/H)

Poor conditioning ⇒ Ckeck wetting of the non conductive surface, because it is very important for glass and resin coverage. (V/H)

⇒ The conditioner must be at the correct concentration, pH and temperature (refer to corresponding data sheet).(V/H)

Poor activation ⇒ Make sure that the Conductor bath parameters are in range (refer to the corresponding data sheet).

⇒ Check REDOX Potential (ROP) measurement, because a lot of mistakes can be performed due to for example poor non- uniform circulation. (V/H)

⇒ The Post-Dip Neopact generally does not cause coverage problems, but the solution must be clear. (V/H)

Poor acid copper plating ⇒ Check the organic components used in the plating bath. Too high concentration of Brightener and/or Leveller may create a lot of coverage problems and cannot be positively influenced by the direct plating process Neopact. (V/H)

Voids on Glass 600x

Voids on Glass 500x

Voids on Glass 150x

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Voiding (PTH Defects)Voids on Glass Fibers only (Compact CP)

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1.5 Voids on Glass and Resin (Compact CP)


Poor hole surface cleaning ⇒ Check Desmear process and etch cleaner for performance. (H)

Poor conditioning ⇒ Seen especially by poor glass coverage, for this check cleaner/conditioner (or Conditioner Mix) for parameter range (refer to the corresponding data sheet). (H)

Poor Adhesion Promoter bath ⇒ Check concentrations, pH and temperature (refer to the corresponding data sheet). (H)

⇒ Check bath life time. A too high amount of MnO2 (sludge) will also cause glass coverage problems. (H)

Poor Polyconduct bath ⇒ Check bath life time by oligomer measurement and visual inspection (color). (H)

⇒ Check organic monomer concentration, pH (very important) and temperature (important especially for the life time) (refer to the corresponding data sheet). (H)

Poor acid copper plating ⇒ Check the organic components used in the plating bath. Too high concentration of Leveller can create a lot of coverage problems and cannot be positively influenced by the direct plating process Compact CP. The effect is more sensitive with Compact CP, than with Neopact. (H)

Glass Void 1000x

Glass Void 500x

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Voiding (PTH Defects)Voids on Glass Fibers only (Seleo CP)

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1.6 Voids on Glass and Resin (Seleo CP)


Poor hole surface cleaning ⇒ Check Desmear process and etch cleaner for performance. (V/H)

Poor conditioning ⇒ Seen especially by poor glass coverage, for this check cleaner/conditioner (or conditioner mix) for parameter range (refer to the corresponding data sheet).

Poor Adhesion Promoter bath ⇒ Check concentrations, pH and temperature (refer to the corresponding data sheet). (V/H)

⇒ Check bath life time. (V/H)

⇒ Check exhaust settings (refer to the corresponding process manual). (V/H)

Poor Pre Dip bath ⇒ Check pH and temperature (very important) (refer to the corresponding data sheet). (V/H)

Poor Polyconduct bath ⇒ Check for foaming. Antifoam AF2 can be added. At least, the module must be modified (refer to the corresponding data sheet). (H)

⇒ Check organic monomer concentration, pH (very important) and temperature (important especially for the life time) (refer to the corresponding data sheet). (V/H)

Poor acid copper plating ⇒ Check the organic components used in the plating bath. Too high concentration of Brightener can create a lot of coverage problems and cannot be positively influenced by the direct plating process Seleo CP. The effect is more sensitive with Seleo CP, than with Neopact.

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Voiding (PTH Defects)Ring Voids / Wedge Voids

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1.7 Ring Voids / Wedge Voids


Poor wetting (gas bubbles) ⇒ Check vibration for performance. (V)

⇒ Check floodbar for performance. (H)

⇒ Use chemistry which will not generate gas.A low surface tension and higher working temperature also enhances performance (hot alkaline cleaner). (V/H)

Direct plating processes ⇒ Check the concentration of organic , especially brightener, in the acid copper plating baths. (V/H) The first sign (before ring voids will appear) is dog-boning or poor throwing power.

Gaps or wedges ⇒ Check drilling performance (prior to Desmear).

⇒ Check lamination process for performance.

⇒ A too strong Desmear can attack the treatment on the copper innerlayer or clad. (V/H)

⇒ Check Black/Brown Oxide or BondFilm processes or other treatments of the copper surface of innerlayers for performance. (V/H)

Resist residues (after panel or pattern plating)

⇒ Check by micro sectioning. More efficient rinsing (additional flood bars) after developing could help. (H)

Tin plating faults (when used as etch resist)

⇒ Also check by micro sectioning. Especially high aspect ratio panels (HARP) PCB’s need an efficient vibration for the pre dip and in electrolytic tin bath as well. (V)

Ring Void (Residue) 500x

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Ring Void (Air Bubble in PTH) Ring Void (Air Bubble in PTH)

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Ring Void (PTH Fault)

Ring Void (PTH Fault) 360 x

Ring Void (PTH Fault) 100x

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Ring Void (Air Bubble / Metal Resist Fault) 500x

Ring Void (Air Bubble / Metal Resist Fault) 500x

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Ring Void (Metal Resist Fault) 400x


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Ring Void (Photo Resist Residues) 100x Ring Void (Photo Resist Residues) 500x

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Wedge Void 1000x

Wedge Void 1000x

Wedge Void with Barrel Problem 1000x

Wedge Voids 1500x

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BTT-PTH · Electronics Division Atotech Deutschland GmbH · Berlin · Germany Voiding Mechanism

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1.8 Voiding Mechanism

Overview: 1.8.1 PTH-Void: LB, Strike/Pattern Plate, Metal Resist .................................................................. 22

1.8.2 PTH-Void: LB, Strike/Panel Plate, Metal Resist .................................................................... 23

1.8.3 PTH-Void: LB, Strike/Panel Plate, Tenting ............................................................................ 24

1.8.4 PTH-Void: LB, Panel Plate, Tenting....................................................................................... 25

1.8.5 PTH-Void: HB, Pattern Plate, Metal Resist............................................................................ 26

1.8.6 Photo Resist Residue Void: LB, Strike/Pattern Plate, Metal Resist....................................... 27

1.8.7 Photo Resist Residue Void: LB, Panel Plate, Metal Resist ................................................... 28

1.8.8 Photo Resist Residue Void: HB, Pattern Plate, Metal Resist ................................................ 29

1.8.9 Metal Resist Void (Gas Bubble): LB, Strike/Pattern Plate ..................................................... 30

1.8.10 Metal Resist Void (Gas Bubble): LB, Panel Plate.................................................................. 31

1.8.11 Metal Resist Void (Gas Bubble): HB, Pattern Plate............................................................... 32

1.8.12 Direct Plating Voids: DP, Strike/Pattern Plating, Metal Resist............................................... 33

1.8.13 Direct Plating Voids: DP, Panel Plating, Metal Resist ........................................................... 34

1.8.14 Direct Plating Voids: DP, Pattern Plating, Metal Resist ......................................................... 35

1.8.15 Gas Bubble in Acid Copper: LB, Strike/Pattern Plating, Metal Resist ................................... 36

1.8.16 Gas Bubble in Acid Copper: LB, Panel Plating, Metal Resist ................................................ 37

1.8.17 Gas Bubble in Acid Copper: HB, Pattern Plating, Metal Resist ............................................. 38

1.8.18 Direct Plating: Gas Bubbles ................................................................................................... 39

1.8.19 Poor Tenting: LB, Strike/Pattern Plating ................................................................................ 40

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Voiding MechanismPTH-Void (cPTH)

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1.8.1 PTH-Void: LB, Strike/Pattern Plate, Metal Resist

After drilling/Desmear Alter low-build

electroless copper (LB) After flash/strike plating

After photo resist application/

imaging /developing After copper pattern plating After metal resist plating

After photo resist stripping After pattern etching After metal resist stripping

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1.8.2 PTH-Void: LB, Strike/Panel Plate, Metal Resist



After panel plating After photo resist application/

imaging /developing After metal resist plating


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1.8.3 PTH-Void: LB, Strike/Panel Plate, Tenting




imaging /developing (tenting) After pattern etching

After photo resist stripping

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1.8.4 PTH-Void: LB, Panel Plate, Tenting


electroless copper (LB) After panel plating

After photo resist application/ imaging /developing (tenting) After pattern etching After photo resist stripping

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1.8.5 PTH-Void: HB, Pattern Plate, Metal Resist

After drilling/Desmear Alter high-build

electroless copper (HB) After photo resist application/

imaging /developing

After pattern plating After metal resist plating After photo resist stripping

After pattern etching After metal resist stripping

The x-section do not show any difference between a PTH void (1.8.5) and a void caused by photo resist residues prior to pattern plating (1.8.8) ! Both cases could be the reason for this kind of void examined by the final test.

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Voiding MechanismPhoto Resist-Void

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1.8.6 Photo Resist Residue Void: LB, Strike/Pattern Plate, Metal Resist



After photo resist application/ imaging /developing (residue) After pattern plating After metal resist plating


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1.8.7 Photo Resist Residue Void: LB, Panel Plate, Metal Resist



After photo resist application/ imaging /developing (residue) After metal resist plating After photo resist stripping


The x-section do not show any difference between a metal resist void/gas bubble (1.8.10) and a void caused by photo resist residues prior to pattern plating (1.8.7) ! Both cases could be the reason for this kind of void examined by the final test.

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1.8.8 Photo Resist Residue Void: HB, Pattern Plate, Metal Resist

After drilling/Desmear Alter high-build

electroless copper (HB) After photo resist application/ imaging /developing (residue)



The x-section do not show any difference between a PTH void (1.8.5) and a void caused by photo resist residues prior to pattern plating (1.8.8) ! Both cases could be the reason for this kind of void examined by the final test.

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Voiding MechanismMetal Resist-Void (Gas Bubble)

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1.8.9 Metal Resist Void (Gas Bubble): LB, Strike/Pattern Plate




imaging /developing After pattern plating After metal resist plating (void)


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1.8.10 Metal Resist Void (Gas Bubble): LB, Panel Plate




imaging /developing After metal resist plating (void) After photo resist stripping


The x-section do not show any difference between a metal resist void/gas bubble (1.8.10) and a void caused by photo resist residues prior to pattern plating (1.8.7) ! Both cases could be the reason for this kind of void examined by the final test.

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1.8.11 Metal Resist Void (Gas Bubble): HB, Pattern Plate

After drilling/Desmear Alter hight-build

electroless copper (HB) After photo resist application/

imaging /developing

After pattern plating After metal resist plating (void) After photo resist stripping


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Voiding MechanismDirect Plating Voids

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1.8.12 Direct Plating Voids: DP, Strike/Pattern Plating, Metal Resist

PTH Void

After drilling/Desmear/PTH After metal resist plating After metal resist stripping

Photo Resist Residue


Metal Resist Void (Gas Bubble)

After drilling/Desmear/PTH After metal resist plating (void) After metal resist stripping

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1.8.13 Direct Plating Voids: DP, Panel Plating, Metal Resist

PTH Void






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1.8.14 Direct Plating Voids: DP, Pattern Plating, Metal Resist

PTH Void






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Voiding MechanismGas Bubble in Acid Copper (cPTH)

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1.8.15 Gas Bubble in Acid Copper: LB, Strike/Pattern Plating, Metal Resist

After drilling/Desmear After low-build

elecroless copper (LB) After flash/strike plating


imaging /developing After pattern plating (gas bubble) After metal resist plating


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1.8.16 Gas Bubble in Acid Copper: LB, Panel Plating, Metal Resist


elecroless copper (LB) After panel plating (gas bubble)


imaging /developing After metal resist plating After photo resist stripping


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1.8.17 Gas Bubble in Acid Copper: HB, Pattern Plating, Metal Resist

After drilling/Desmear After high-build

elecroless copper (HB) After photo resist application/

imaging /developing



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Voiding MechanismGas Bubble in Acid Copper (Direct Plating)

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1.8.18 Direct Plating: Gas Bubbles

Strike/Pattern Plating


Panel Plating


Pattern Plating


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Voiding MechanismPoor Tenting

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1.8.19 Poor Tenting: LB, Strike/Pattern Plating


elecroless copper (HB) After flash/strike plating


imaging /developing (fault) After pattern etching

Panel Plating

After photo resist stripping After photo resist stripping

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Voiding BMV or HARP Coverage Problems

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1.9 BMV or HARP Coverage Problems


Poor mechanical or laser drilling ⇒ Check result prior to the wet chemical processes (a special drilling know how is necessary).

Poor surface cleaning prior to PTH ⇒ Check Desmear and cleaning process related to chemistry and equipment for performance. (V/H)

Poor PTH technology (liquid exchange in BV/BMV, HARP-through hole)

⇒ Do not use normal vertical technology, which is not able to guarantee a uniform liquid exchange. (V)

Poor equipment and chemistry ⇒ Employ vibration and air shock system for vertical applications. (V) – Otherwise:

⇒ Use special designed horizontal equipment (Uniplate) for Desmear/cleaning and electroless copper processes for BMV’s. (H)

Poor quality of copper deposition in BMV's

⇒ Use specially adapted processes based on electroless copper or conductive polymers. We do not propose the direct plating process Neopact for BMV’s. (V/H)

Poor acid copper plating ⇒ For blind microvia’s (BMV’s) and high aspect ratio panels (HARP), pulse plating is recommended. However, each case must be considered according to the aspect ratio. (V/H)

Micro Via (Wetting Fault) Micro Via (Conductivity)

Issue



Voiding BMV or HARP Coverage Problems

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High AR panels Voids

High Aspect Ratio Panel 2.4 mm

High AR panels Voids

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Voiding Barrel Cracks due to Stress after Thermal Treatment

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1.10 Barrel Cracks due Stress in Plated Copper after Thermal Treatment Barrel Cracks can be misinterpret as ring voids an can be observed by micro sectioning.


Poor base material ⇒ Incompletely (non-uniform) cured (polymerization). A baking (~4 hours at 140°C) prior to Desmear/ PTH could help.

⇒ Also exclude moisture by baking.

⇒ If possible, use base materials with higher Tg point.

Poor acid copper plating ⇒ Unsuitable plating parameters (current density too high, pulse parameters too strong, inept current distribution, brightener/leveller concentration)

Poor thermal treatment ⇒ Test conditions too strong in relation to the kind of base material ?

⇒ Bake approximately 1 hour at 150°C prior to Hot Air Levelling (HAL) or soldering.

Barrel Crack 100x Barrel Crack 500x

Barrel Crack 150x

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Pull-away Adhesion Problems on Resin prior Thermal Treatment

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2. Pull-away: Adhesion Problems on Resin prior Thermal Treatment This fault can be observed by micro-sectioning prior to thermal treatment. At worst case pull-away can cause voids.


Poor base material ⇒ Some base materials contain additives which create contamination’s. Please check base material data sheet !

Poor or wrong drilling condition ⇒ Too high drilling (cutting) speed creates hydrophobic (highly cured) resin surfaces. Adjust drilling parameters.

⇒ Drills are used for too many hits (before re-pointing). Adjust drilling parameters.

⇒ Inefficient heat dissipation. Adjust drilling parameters.

⇒ Unsuitable back-up and entry cover material (in worst case based on phenolic resin).

⇒ If the drilling package too high. Adjust drilling parameters.

Poor Desmear/cleaning ⇒ Inefficient or wrong Desmear and cleaning procedure. (V/H)

⇒ Check for plasma or ultrasonic support.

Poor activation ⇒ Check conditioner and activator related to over-activation for performance. (V/H)

Poor quality of electroless copper deposition

⇒ If the electroless copper bath is too active, check process parameters. (V/H)

⇒ Reduce immersion time. (V)

Poor micro-sectioning ⇒ Incorrect preparation in cutting, grinding, filling compounds, etc. (refer to IPC-TM-650 2.1.1).

Issue



Pull-away Adhesion Problems on Resin prior Thermal Treatment

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Pull-away 100x Pull-away 32x

Pull-away 200x

Issue



Resin Recession Adhesion Problems on Resin after Thermal Treatment

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3. Resin Recession – Adhesion Problems on Resin after Thermal Treatment

This fault can be observed by micro-sectioning after thermal treatment.


Poor base material ⇒ Incompletely (non-uniform) cured (polymerisation). A baking (~4 hours at 140°C) prior to Desmear/ PTH could help.

⇒ Also exclude moisture by baking.

⇒ If possible, use base materials with higher Tg point .

Poor drilling condition ⇒ Avoid substrate stress.

⇒ Maybe unsuitable back-up and entry cover material (i.e. based on phenolic resin).

Poor desmearing ⇒ Too strong swelling conditions. Check desmear parameters. (V/H)

⇒ Make a test cycle without the swelling step and compare to conventional treatment. (V/H)

⇒ Use plasma-etch, if it is possible.

Poor thermal treatment ⇒ Test conditions too strong in relation to the kind of base material. Check base material specifications.

⇒ Bake approximately 1 hour at 150°C prior to Hot Air Levelling (HAL) or soldering.

Poor micro-sectioning ⇒ Bake for at least 2 hours at 120°C prior to Solder shock according to IPC-TM-650 2.6.8.

⇒ Incorrect preparation in cutting, grinding, filling compounds, etc. (refer to IPC-TM-650 2.1.1).

Issue



Resin Recession Adhesion Problems on Resin after Thermal Treatment

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Resin Recession 200x Resin Recession 200x

Resin Recession 80x Resin Recession 500x

Resin Recession 200x

Issue



Wicking Copper Re-Plating

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4. Wicking – Copper Re-Plating Wicking reduces insulation between two tracks and can be observed by micro-sectioning and resistance measurements. Avoidance of wicking is a precondition for fine line - and/or SMD technology.


Poor base material ⇒ Poor glass fiber quality, including glass fiber finish (mostly Silane substances).

Poor drilling condition ⇒ Avoid substrate stress.

Poor desmearing ⇒ Use halide-free smear removal chemistry.

⇒ Avoid swelling conditions with strong organic solvents.

Poor PTH conditions ⇒ Also use halide-free chemistry. Especially chlorides and fluorides cause wicking.

⇒ Avoid strong acid based Pd/Sn catalysts and use alkaline ionic activator (Neoganth Series). (V/H)

Wicking

Wedge Void

D-Effect

ICD

Issue



Wicking Copper Re-Plating

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Wicking

Wicking

Wicking (34 µm) 1000x

Issue



Blistering & D-Effect Adhesion Problems on Copper Surfaces

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5. Blistering and D-Effect – Adhesion Problems on Copper Surfaces This is a copper to copper adhesion problem mostly visible prior to a thermal treatment

procedure.


Copper passivation ⇒ Check deburring and etch process prior to Desmear/PTH.

Poor desmearing ⇒ Improve Desmear performance. (V/H)

⇒ Use a special cleaner with ultrasonic support after Desmear. (V/H)

Poor cleaning (PTH) ⇒ Use the Securiganth Cleaner 902 (V) or ULS at high temperature and/or ultrasonic support. (V/H)

Poor conditioning PTH ⇒ Check conditioner for performance, maybe conditioning agent is not suitable (i.e.: too strong). (V)

Poor etch cleaning (PTH) ⇒ Check parameters and working conditions (refer to data sheet). (V/H)

Poor activator bath (PTH) ⇒ Avoid an over-activation and for this check the concentrations, etc. (V/H)

Poor reducer bath (PTH) ⇒ Check parameters (refer to data sheet). (V/H)

Poor quality of electroless copper bath (PTH)

⇒ Decrease the activity of the electroless copper bath. (V/H)

⇒ Check the density (refer to data sheet). (V/H)

⇒ Reduce the immersion time. (V)

Blistering 5x Blistering 50x

Issue



Blistering & D-Effect Adhesion Problems on Copper Surfaces

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Blistering

Blistering

D-Effect

D-Effect

D-Effect 1000x

D-Effect 1000x

Issue



Innerlayer Connection Defects (ICD’S) Prior and After Thermal Treatment

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6.1 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Prior and After Thermal Treatment

Check by micro-sectioning directly after polishing without etching !


Copper passivation ⇒ Check deburring and etch process prior to Desmear/PTH

Poor drilling ⇒ Avoid entry- or back-up materials which are based on phenolic resin.

Poor copper crystal structure (changed at drilling by thermal effect)

⇒ Remove (horizontal with Etch Cleaner) 2 to 4 µm copper prior to Desmear/PTH (Bosch K8 prerequisite). (V/H)

Poor desmearing ⇒ Improve Desmear performance. (V/H)

⇒ Use a special cleaner with ultrasonic support after Desmear. (V/H)

⇒ Use ultrasonic support in the permanganate-etch and make a test with two Desmear cycles (the second without the Sweller). (V/H)

Poor cleaning (PTH) ⇒ Use the Securiganth Cleaner 902 (V only ) or ULS at high temperature and/or ultrasonic support. (V/H)

Poor conditioning PTH ⇒ Check conditioner for performance, maybe conditioning agent is not suitable (i.e.: too strong). (V)

Poor etch cleaning (PTH) ⇒ Check parameters and working conditions. (V/H)

⇒ Check rinsing conditions and/or work additionally with an acid dip after etching. A drag-in of etch cleaner into the activator could cause a lot of problems !

⇒ Mostly, a higher etch rate does not help (factors before etching are more important). (V/H)

Poor activator bath (PTH) ⇒ Avoid an over-activation and for this check the concentrations, etc. (V/H)

Poor reducer bath (PTH) ⇒ Check parameter (refer to data sheet). (V/H)

Poor electroless copper bath (PTH) ⇒ Decrease the activity. (V/H)

⇒ Check the density (refer to data sheet). (V/H)

⇒ Reduce the immersion time. (V)

⇒ Mostly, the use of a low speed is better than a high speed bath. (V/H)

Be continued...

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Innerlayer Connection Defects (ICD’S) Prior and After Thermal Treatment

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Sources of Defects (cont.) How to Avoid... (cont.)

Poor acid copper plating ⇒ Check handling and pre-treatment conditions between electroless and acid copper plating.

⇒ Unsuitable plating parameters (current density too high, pulse parameters too strong, inept current distribution)

ICD 1000x ICD (etched) 1000x

ICD 500x ICD 1000x

Issue



Innerlayer Connection Defects (ICD’S) Rest Smear

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6.1.1 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Rest Smear

ICD 500x ICD 1400x

ICD 8300x EDX: C, O, Br, Si - Smear Rest Smear at Copper Clad

Copper Smear on Innerlayer Resin Smear on Innerlayer

Issue



Interlayer Connection Defects (ICD’S) Poor Copper Crystal Structure

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6.1.2 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Poor Copper Crystal Structure

Re-crystallization of innerlayer 1500x

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Innnerlayer Connection Defects (ICD’S) Innerlayer Burning

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6.1.3 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Burning at Innerlayer Interface

Innerlayer Burning 1000x Innerlayer Burning 2500x

Innerlayer Burning 1000x Innerlayer Burning 5000x

NOTE: Burning at innerlayer is no PTH fault, but related to poor acid copper plating or circuit design.

Issue



Innnerlayer Connection Defects (ICD’S) Corner Cracks

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6.1.4 Innerlayer Connection Defects (ICD’s) and Corner Cracks – Corner Cracks

Corner Crack (after Solder Shock Test) 1000x Corner Crack (after Solder Shock Test) 1000x

Corner Crack (after Solder Shock Test) 1000x Corner Crack (after Solder Shock Test) 2000x

NOTE: Do not mix up ICD’s with foil/copper clad cracks as shown at [6.2]. Foil/copper clad cracks are no PTH related faults !

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Foil/Copper Clad Cracks After Thermal Treatment

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6.2 Foil/Copper Clad Cracks – After Thermal Treatment Foil cracks are often interpreted as ICD’s, but the crack is far from the innerlayer connection. Check by micro-sectioning after etching !


Poor/wrong innerlayer/ copper clad material

⇒ Use the correct copper clad material.

Foil Crack prior Etching Foil Crack after Etching

Crack in Copper Clad Foil Crack

Issue



Pocket Voids After Thermal Treatment

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7.1 Pocket Voids – After Thermal Treatment Pocket voids are mostly caused by the Silane finish coating of the glass fibers. A poor quality of this finish, could create a capillary effect, which enables a penetration of chemistry from the subsequent wet processes. This final fault can only be checked by micro-sectioning after solder shock test.


Base material ⇒ Bake approximately 4 hours at 140°C prior to the Desmear process.

⇒ Make a cross check with other types of base materials.

Desmear ⇒ Maybe the Desmear is excessive caused by strong swelling conditions in the alkaline permanganate process. For this reason, make a test without using the swelling step and compare the results. If the Pocket Voids are still observed, the base material is not suitable for this process. (V/H)

Pocket Void 159x Pocket Void 159x

Issue



Pocket Voids After Thermal Treatment

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Pocket Void 533x

Pocket Voids Pocket Void 394x

NOTE: Do not mix up pocket voids with delamination as shown at [7.2]. Delamination is no PTH related fault !

Issue



Delamination Before and After Thermal Treatment

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7.2 Delamination – Before and After Thermal Treatment Delamination is caused by the pressing/curing faults at multilayer production. Delamination can cause PTH faults, but the origin is not related to PTH processes. This final fault can only be checked by micro-sectioning. Often only be seen after thermal treatments.


Base material ⇒ Use suitable base materials and pressing parameters

Delamination (after solder shock test) 40x Delamination (after solder shock test) 160x

Delamination (after solder shock test) 160x Delamination (without thermal treatment)

Issue



Negative Etch Back Copper Innerlayer Recession

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8.1 Negative Etch Back– Copper Innerlayer Recession This fault, also called reverse-etch back refers to the condition where the copper interconnect is recessed into the drilled hole wall. It is visible by micro-sectioning and could also be a cause for a fault at the final electrical test.


Poor drilling ⇒ Check the drilling conditions.

Poor innerlayer/copper clad quality ⇒ Inconsistent copper clad thickness and quality. Check by SEM in combination with EDX.

Desmear ⇒ Process too weak. Check parameter settings. (V/H)

⇒ Wrong Reducer/Neutralizer (Cleaner) which removes too much copper. Check Parameters. (V)

Poor Desmear and PTH equipment performance

⇒ Avoid formation of potential difference by electrically earthling the tanks. (V)

Poor etch cleaner (PTH) ⇒ Avoid halides in combination with oxidizing agents. (V/H)

⇒ Maybe a too high etch rate at the innerlayer by exothermic reaction caused by poor liquid exchange. In this case work with stronger air agitation. (V)

⇒ If possible, work with Securiganth Etch Cleaner C (but not for basket lines). (V)

Negative Etch Back Negative Etch Back

Issue



Negative Etch Back Copper Innerlayer Recession

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Negative Etch Back

Negative Etch back 700x Negative Etch Back 1000x

Issue



(Positive) Etch Back Excessive Etch Back of Dielectric Material

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8.2 (Positive) Etch Back– Excessive Etch Back of Dielectric Material Special printed circuit high-tech boards (as used for space travel or military application) need a triple interface bonding on the copper innerlayers. In this case a combination of plasma and permanganate etch is recommended. The copper innerlayer should stand out between 2 and 8 µm. Perfect quality could be reached when glass etch back have take place additionally.


Base material ⇒ Use suitable base materials and pressing parameters

Desmear ⇒ Process too strong – adjust Desmear parameters. (V/H)

⇒ Wrong Sweller agent (concentration, pH, immersion time). The resin is softens too much (V/H)

⇒ Too strong permanganate etch bath (temperature, permanganate/sodium hydroxide content, immersion time). Check parameters. (V/H)

(Positive) Etch Back 1000x

(Positive) Etch Back 1000 x

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Star Burst After Electroless Copper Plating

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9. Star Burst – After Electroless Copper Plating This fault is caused by excessive electroless copper plating around the hole entrance (volcano-effect). It can be examined visibly – best by using a magnifying glass.


Contamination on the copper surface (promoter)

⇒ Check deburring process for performance especially the roller material.

⇒ Check cleaning procedure prior to Desmear/PTH.

Poor copper crystal structure (changed during drilling by thermal effect)

⇒ Avoid high contact force during drilling.

Etch Cleaner (PTH) ⇒ Check bath parameters and air agitation for performance (uniform and powerful). (V)

Reducer (PTH) (most important)*

⇒ When using Reducer Neoganth, the concentration of NaOH must be reduced to 1 g/l (pH 11- 12.5). (V)

⇒ By working with Reducer Neoganth 406/WA, a pH between 5 and 6 – controlled by acetic acid – might also help. (V/H)

Electroless Copper ⇒ Reduce activity (temperature first). (V/H)

⇒ Reduce immersion time. (V)

⇒ Check the density. If to high, discharge half volume of the bath and replace by a half new make-up. (V/H)

⇒ Check the circulation power. (V)

* NOTE : The first proposal is actually practical experience – the second should give good acceptability. But it is certain that both actions influence the activity of the electroless copper plating.

Star Burst 40x Star Burst 750x

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Blow Holes Outgassing after Thermal Treatment

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10. Blow Holes – Outgassing after Thermal Treatment Blow Holes, also called outgassing, occur after Hot Air Levelling (HAL), soldering or solder shock tests and are visible or can be examined by micro-sectioning. An excellent PTH result is the prerequisite for a void-free electro-plating, which is very important to obtain good results.


Poor base material ⇒ Base material incompletely cured – Bake approximately 4 hours at 140°C prior to the Desmear process.

⇒ Avoid moisture (by baking)


Hole wall too rough (prior to Desmear) ⇒ Base material incompletely cured – Bake approximately 4 hours at 140°C prior to the Desmear process.

⇒ Avoid moisture (by baking)

⇒ Check the drilling parameters.


Poor hole cleaning (after desmear) ⇒ Excessive Desmear conditions create strong protruding glass fibres. Adjust parameters. (V/H)

⇒ Dust, particles and smear residues must be removed prior to the PTH processes. (V/H)

Poor PTH / acid copper plating (voids) ⇒ Check the PTH result by backlight test.

⇒ Check for resist residues prior to acid copper plating. (V)

⇒ Check electrolytic tin plating result if it is used as etch resist. (V)

Poor acid copper plating ⇒ Check pre-treatment prior to plating. (V)

⇒ Check the copper plating quality (thickness, throwing power, etc.). (V/H)

NOTE: Baking (approximately 1 hour at 150°C) prior to thermal treatment will most often reduce the blow hole problem !

Issue



Blow Holes Outgassing after Thermal Treatment

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Blow Hole 20x Blow Hole 132x

Blow Hole 771x

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Pink Ring (Red Ring) on Black Oxide Layer

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11. Pink Ring – (or Red Ring) on Black Oxide Layer The Pink Ring problem is an attack of the Black Oxide-layer, also known as Red Ring or the “haloing” phenomenon. It is a preliminary stage in creating wedges and finally wedge voids and is especially dangerous in combination with Direct Plating PTH processes.


Poor innerlayer/copper clad quality ⇒ The surface must be even and free of pores.

Poor chemical cleaning ⇒ Check the result (the copper surface must be uniformly clean). (H)

Poor lamination procedure ⇒ Check the prepreg quality and the press cycle parameters.

Poor black oxide process ⇒ Check the process parameters. (V/H)

⇒ Use a reduction step (important!). (V/H)

⇒ Do not dry with too high temperature. (V/H)

⇒ Check the results like thickness, adhesion, etc.

Poor drilling ⇒ Check the drilling procedure, especially for small holes.

Poor desmearing ⇒ Maybe too excessive. Adjust parameters. (V/H)

Poor PTH process ⇒ Check after Etch Cleaner. (V/H)

⇒ Use a process which is free of hydrochloric acid (HCl) (important!). (V/H)

Poor acid copper plating ⇒ Acid copper baths may attack the granular structure of oxide layers. (V/H)

NOTE: When using reduced black oxide or better the new BondFilm process, the pink ring problem will not occur.

Issue



Pink Ring (Red Ring) on Black Oxide Layer

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Pink Ring (Black Oxide) Through Hole (Reduced Black Oxide)

Wedge Void 500x Pink Ring 25x

Wedge Void / Delamination on Treatment (Black Oxide) Side

D-Effect

Issue



Tooling Hoole Problems) After Electroless Nickel/Gold Plating (ENIG)

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11. Tooling Hole Problems– After Electroless Nickel/Gold Plating (ENIG) The activation (mostly by Palladium), which takes place during the PTH processes, must be removed or deactivated prior to the final electroless Nickel/Gold (ENIG) finishing procedure. The biggest problems have been observed in combination with the Direct Plating process Neopact, followed by classical PTH (if standard working conditions is followed properly). The direct plating processes Compact CP and Seleo CP are easy to handle for this issue, this process is Palladium free.


Hole walls too rough ⇒ Check base material in combination with the drilling conditions.

⇒ Check Desmear process for performance. (V/H)

Poor PTH process ⇒ Avoid over-conditioning and activation. (VH)

Poor copper etching ⇒ Make sure that all the copper in the tooling holes is completely etched off.

⇒ Use Deactivation FMD 89 after the etching process.

Poor electroless Nickel/Gold (Aurotech) ⇒ Use the Cleaner Pro Active DP prior to ENIG.

⇒ Avoid a too active electroless nickel bath and increase the stability by using the Additive TH.

NOTE: A post drill or a permanganate treatment prior to the electroless Nickel/Gold (ENIG) process (if possible) also helps to avoid nickel coverage in the tooling holes.

x-Section of a Tooling Hole:

Electroless Nickel/Gold Deposition (ENIG)

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Typical Phenomena in Cross Section of Plated Through Holes

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Typical Phenomena in Cross Section of Plated Through Holes

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Typical Phenomena in Cross Section of Microvias

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Picture 1

Typical Phenomena in Cross Section of Plated Microvias

plating through hole

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