managing temperature sensitive components in pb-free … · 2011-05-31 · components in pb-free...

Server and Technology Group

© 2011 IBM Corporation

Managing Temperature SensitiveManaging Temperature Sensitive

Components in PbComponents in Pb--free Assembliesfree Assemblies

J.R. Wilcox, C.T. Grosskopf, M.S. Kelly, M.S. ColeIBM Integrated Supply Chain


© 2011 IBM Corporation2 2011 IBM Power Symposium, RTP, NC

Pb-free Solder Assembly at IBM

IBM Server team…... designs and assembles complex PCBAs for server class

products; systematically transitioning to Pb-free assembly.

... has developed rigorous practices for ensuring extended field performance and reliability of Pb-free assemblies.

... expects its suppliers to take equal care in designing and manufacturing the components and sub-assemblies provided for use in IBM systems.

... shares best practices learned from our Pb-free assembly experience.



Topics

Component Process Sensitivity

Industry Specifications

J-STD-075 Evaluation and Classification

Using Sensitivity Data in Assembly Process Definition

Post Solder Attach Temperature Sensitivity

Take home messages…



IBM ES 44V5066 for Power Assemblies

DOES: Define allowable RoHS material selections (through 97P3864). Define minimum qualification testing for IBM Power Assemblies. Establish minimum functional reliability through accelerated stress

testing:– ATC (-40C / 90C / 1cph) 750 cycles [not powered]– TH&B (85C / 80RH / 15V) 500 hours [not powered]– Random Vibration (2G(rms) /10 min) and up [powered]

Require product functional survival of 5X reflow cycles.

DOES NOT: Identify procedures for proper definition of a Pb-free solder

assembly process. Classify process sensitivity of the assembled power product.

!



Elevated Solder Processing Temperatures

Full Pb-free assembly drives a minimum 230C solder joint.PCB and attached components reach higher temperatures:

245C – 260C.

PTH & REWORK

SMT REFLOW

SMT REWORK

SnAgCuProcess Windows SnPb

280

240

220

180

200

260

Pea

k Te

mpe

ratu

re o C C

183C SnPb melting pt.

SnPb

SnAgCu

217C SnAgCu melting pt.

230C SnAgCu solder joint temperature



Temperature Sensitive Devices

Temperature sensitive device families currently acknowledged by the electronics industry:

– aluminum and polymer aluminum capacitors

– film capacitors

– molded tantalum capacitors (polymer & fused)(exception: standard MnO2 type non-fused are not sensitive)

– fuses

– inductors and transformers with wire coils

– non-solid state relays

– LEDs (Light Emitting Diodes)



Component Process Sensitivities

The more common process sensitivities encountered today are limitations with respect to:

– pre-heat time and T

– time above liquidus (217C)

– peak reflow temperature

– time within 5C of peak T

– number of reflow passes

– flux exposure

– cleaning processes

Temperature Sensitivities

(solder reflow)

Other Process Sensitivities

Temperature Sensitivities(post solder process)

– solder pot temperature

– preheat temperature

– solder contact time

– encapsulant cure

– moisture bake

waveSMT



Process Sensitive Devices

Overheating process sensitive devices during SMT reflow or PTH wave soldering can result in serious reliability failures:

Immediate electrical or catastrophic fails

Early fails in the life of the electronic product.

Examples. If thermally overstressed,

–Aluminum and polymer aluminum capacitors may exhibit bulging or venting of the metal can;

–Fuses can experience reduction in the maximum limiting current of the fuse element (nuisance blows).

– Inductors and transformers with coils can experience degradation of the lacquer coating of the coil wire, leading to intermittent shorts.


© 2011 IBM Corporation9 2011 IBM Power Symposium, RTP, NC9 Building the on demand supply chain © 2007 IBM Corporation

Warpage;Loss of dimensional toleranceSMT Connectors

-LEDs

-Non Solid State Relays

Reduced limiting currentFuses

Breakdown of conductor coating; intermittent shortsInductors / Transformers

DelaminationDouble Carbon Layer Capacitors

Fairly robustPolymer Tantalum Capacitors

Increased loss tangentFilm Capacitors

Polymer Aluminum Capacitors

Seal damage;

early electrolyte dry out

SMT Aluminum Capacitors

Time Dependant Failure ModeComponent Type

Temperature Sensitive Components

The negative consequences of over-temperature exposure varies.


© 2011 IBM Corporation10 2011 IBM Power Symposium, RTP, NC10 © 2007 IBM Corporation

100F electrolytic capacitor after Pb-free reflow After M. Wickham, et al., 2003

SMT electrolytic capacitor body burnas a result of Pb-free hand soldering operationsIBM 2007

Cracks in the end of the polyester capacitorAfter M. Wickham, et al., 2003

Temperature Sensitive Components



Temperature Sensitive Component Standards

J-STD-020: “Moisture/Reflow Sensitivity Classification for Nonhermetic Solid State Surface Mount Devices”– applies to surface mount soldered components only

– presumes different expected reflow profiles based on package volume and height

– assigns different reflow profiles for SnPb and Pb-free solder assembly• Tpeak = 245C, 250C, or 260C [Pb-free]

– assigns Moisture Sensitivity Level (MSL) Rating

– not formally applicable to passive components and connectors



J-STD-020 is widely accepted and adhered to by suppliers of integrated circuit components.

As increasingly complex server boardassemblies transition to Pb-free assembly,some concerns with the defined J-STD-020 limits have been identified.

Extended time above liquidus (TAL) conditions are of primary concern– high thermal mass card assemblies built using

complex fixtures and shielding can extend TAL times well beyond the rated 150 second limit.

– 300+ second required TAL time exposes components beyond their rated capability.

Process Sensitivity Standards: J-STD-020



Temperature Sensitive Component Standards

J-STD-075: “Classification of Non-IC Electronic Components for Assembly Process”– targets ‘non-IC’ components but can be applied to any commodity

soldered to a PCB (connectors, etc)

– requires all components be tested to same ‘worst case’ Pb-free reflow profile metrics, e.g., highest peak temperature

– addresses Pb-free wave soldering as well as Pb-free surface mount soldering• SMT: Tpeak = 245C, 250C, or 260C (package body temp); • PTH: Tpeak = 275C (wave solder pot temp)

– assigns Process Sensitivity Level (PSL) Rating



J-STD-075, recently published, has not yet been widely adopted by the passive component industry.

Devices that cannot meet baseline Pb-free soldering profiles without degradation are classified as being “Process Sensitive”

– Defines base Pin-Through-Hole (PTH) wave solder profile

– Defines base Surface Mount (SMT) reflow solder profile

– SMT profile is linked to J-STD-020 reference profiles

www.global.ihs.comProcess Sensitivity Standards: J-STD-075

Components deemed process sensitive per J-STD-075 may or may not be an issue on any given card assembly

– e.g., a large mass passive may only be rated to 250C, and therefore ‘sensitive’, but never reaches 250C in actual PCBA designs.

Must explicitly profile the ‘sensitive’ component on the card in question– e.g., ceramic caps have 3C/s cooldown limit but never encountered in practice.



J-STD-075: Evaluation and Classification

J-STD-020 defines temperature and duration ranges for SMT reflow profile parameters– e.g., Table 5-2 in J-STD-020 states that the time above liquidus

(TAL) requirement is 60 – 150 seconds

J-STD-075 instead requires that the device under evaluation be tested at the maximum value of the range. – e.g., the device must be capable of withstanding 150 seconds

above 217C to avoid a TAL sensitivity rating.




Classification Reflow Profile; J-STD-020, Figure 5-1

worst case reflow profile metrics



J-STD-075 Evaluation and ClassificationBase SMT reflow profile, per Table 5-2, J-STD-020D

Requirement of 3 reflows stated in clause 5.6 of J-STD-020

reflowprofilemetrics




Tables 5-1, 5-2, 5-3 in J-STD-075 provide the PSL (Process Sensitivity Level) classification scheme

PSL classification will always contain 2 characters and may require an optional 3rd character – 1st character identifies process:

W = wave, R = reflow – 2nd character identifies maximum

peak temperature limitation– 3rd character identifies other process

limitations as defined in Table 5-3

3rd character is omitted when – device is not sensitive (R0, W0), or when– the only sensitivity is peak temperature (R5, W4)

XYZsolder process

(W or R)

peak temperature limit(number)

other processsensitivities

(letter)



PSL Classification Example

SMT aluminum capacitor– 100F, 25V

– Size = 6.8mm x 6.8mm x 8mm

Supplier A, Qualification assembly profile metrics:– Preheat 150-180C for 120sec

– Peak temp 260C for 5 sec max

– Time above 217C of 70sec

– Number of reflows = 2X




Peak reflow temperature requirement per table 4-2 in J-STD-020D for a device of this size is 245C– Package Volume: 6.8 x 6.8 x 8.0mm = 370mm3, – Package Height: 8.0mm is ≥2.5mm

Peak temperature of 260C, exceeds requirement of 245C But what about other profile metrics?




Preheat 150-180C for 120sec: Not worst case.– requirement is 150 - 200C for 120 seconds

Time above 217C of 70sec: Not worst case.– requirement is 217C for 150 seconds

5 sec within 5C of peak temp: Not worst case.– requirement is 30 seconds

Number of reflows = 2 times: Not worst case.– requirement is 3 reflow passes

This device from Supplier A is not qualified to reflow profile extremes and is therefore deemed temperature sensitive.

A PSL rating must be generated.




PSL = R4N

R = Reflow,W = Wave

Table 5-3 PSL 3rd Character

Table 5-2 Reflow Solder PSL Classification



PSL Data Collection and Management

PSL information for each supplier part number (PN) must be gathered and stored– PSL rating

– Identify limiting values for each sensitivity for example,• Peak Temperature• Time Above Liquidus (TAL)• Comments fields for information on cleaning or other limitations

Information not easily obtained, nor in readily usable format



PSL Data Collection and Management

Need software tool to identify all sensitive devices on assembly Bill of Materials (BoM)– For devices with multiple sources, must pull data for all possible

suppliers and identify ‘worst case’

Need to monitor temperature of all identified sensitive devices during solder reflow profile development– Many thermocouples; possibly multiple profile boards– Where possible, modify profile settings to ensure temperature

limitations for all devices are not exceeded

Special processes required for very sensitive devices



IBM Example PCBA BoM Review

Complete Bill of Materials– IBM PN, Quantity, Ref Des Location, Front/Back

– Convert into spreadsheet format.

– Pull BoM details from part number data base

– Bounce PN data off of “Temperature Sensitive BoM Scrub Tool”

– Supplier/ Supplier PN, Package, I/O count, Lead spacing, Lead size, (BGA) Ball metallurgy

– Data not available from PN database must be found by searching individual supplier’s web sites or contacting supplier directly



BoM Scrub Tool Output

TemperatureSensitiveComponents



Using PSL Data in PCBA Development

Define Thermocouple locations for each initial attach process (SMT, wave) and each special rework process:

Along with the T/C’s at traditionally critical sites, e.g.,– QFNs – PCB laminate– BGAs

must include indentified temperature sensitive SMT components– electrolytic capacitors, tantalum capacitors– older fuses and LEDs– very large inductors – connectors/ battery holders/ switches

and temperature sensitive PTH Parts– wave solder and rework is the most difficult lead-free solder process


© 2011 IBM Corporation30 2011 IBM Power Symposium, RTP, NC30 © 2007 IBM Corporation

TSC Monitoring Example

4 Crystals

4 Oscillators6 SMT Electrolytic Capacitors1 Tantalum Capacitor

15 total temperature sensitive device placements

4 Crystals

4 Oscillators6 SMT Electrolytic Capacitors1 Tantalum Capacitor

15 total temperature sensitive device placements

Temperature Sensitive Components: (15 total) Aluminum Capacitors Polymer Tantalum capacitors/Fuses Crystals Oscillators

COMPONENT BODYMEASUREMENT(PLASTIC / METAL BODY)

LEAD SOLDER JOINTMEASUREMENT(ATTACH TO EXPOSED FILLET)

SMT ElectrolyticCapacitor Example

COMPONENT BODYMEASUREMENT(PLASTIC / METAL BODY)

LEAD SOLDER JOINTMEASUREMENT(ATTACH TO EXPOSED FILLET)

SMT ElectrolyticCapacitor Example



Using PSL Data in PCBA Development

Finding out after that a device requires hand soldering after profile development is not optimal.– Far better to identify very sensitive devices early in design phase,

and not use if at all possible (select alt. devices or alt. suppliers)

– Designers need to be educated in TSC management practices

For new devices, PSL data may not yet be available.

Cannot use electrical test or visual inspection to validate profile.– Latent damage most typically not immediately evident

– At times, possible to confirm acceptability of marginal situations directly with component supplier.



Post Solder Attach Temperature Exposures

Solder reflow is not the only elevated temperature required in circuit card assembly operations.

Post solder thermal exposures are typically at lower temperatures (90 – 125C) but for longer times.

Thermal Cures– Heatsink Thermal Interface Materials– Encapsulants, Adhesives

Extended Moisture Bakes– Rework preparation

Some components known to be sensitive to extended temperature exposures



Post Solder Attach Sensitivity

Post solder attach temperature sensitive components not covered by any industry specification. Be wary.

Press-fit and socketed devices are not qualified to any solder attach thermal profiles

PTH devices are only qualified to solder wave/fountain thermal conditions

– Only leads are subjected to molten solder

– Supplier may not have simulated preheat of device body




Range of Maximum Temperatures Allowed by Various Suppliers

125C up to ‘Not Sensitive’PTH tantalum capacitors

105 to 125CPTH film capacitors

85C up to ‘Not Sensitive’Fuses and polymer PTCs(Positive Temperature Coefficient)

85C up to ‘Not Sensitive’PTH aluminum electrolytic capacitors

85C up to ‘Not Sensitive’PTH LEDs

70 to 85CButton Cell Batteries

As was the case for reflow sensitivities, post solder attach temperature sensitivities must be identified uniquely for each supplier part number.




Failure modes similar to initial attach Immediate electrical or catastrophic

fails– PTH LEDS with organic encapsulants may

expand to point that internal wire bonds break

Early fails in the life of the electronic product– Aluminum and polymer aluminum

capacitors may exhibit bulging or venting of the metal can

– Button cell batteries may have seals broken and lose electrolyte

Broken stitch bond in PTH LED Rated to 105C; baked at 125C.

PTH (organic) LED

polymer Al capacitor

Excessive bake temperature Capacitor shorted & burned.



Post-Solder Processes of Concern

Short duration bakes– Adhesive and encapsulant cures

• e.g., heatsink attach, underfill encapsulation, device encapsulation– 130C for 90 minutes– 150C for 40 minutes

Long duration bakes– Moisture bake

• required prior to SMT rework to ensure no damage to ‘nearest neighbors’ of device being removed or to underlying PCB laminate

– 125C for 24 and 48 hours



Post-Solder Processes of Concern

Card level temperature cycling– Screen for soldering defects

– 0 to 100C for 1 cycle/hour, 15 minute dwells

– Some device families are not qualified to these conditions

Some suppliers state that their indicated maximum temperatures only apply if no bias is applied during the stress



Using Post Solder Attach Sensitivity Data

Can use similar method of storing post solder attach sensitivitydata as with solder process PSL information

Data must be gathered and stored for each supplier part number– Short duration bake maximum temperature– Long duration bake maximum temperature– Thermal cycling peak temperature

• Peak temperature generally matched short duration bake Some suppliers had to perform additional qualification testing

to determine if they could support use of their devices to aboveprocesses.



Using Post Solder Attach Sensitivity Data

Software for PSL management can also be used to identify devices on card BoM that are sensitive to post attach processes– For devices with multiple sources, must pull data for all– Define processes to accommodate worst case supplier

Only need to identify oven/chamber peak temperature– Profiling with thermocouples not required

If process condition exceeds device limits:– Change conditions of the process

• Longer duration bake at lower temperature– Perform process prior to attaching the sensitive device(s)

• Best solution for ‘press-fit’ and socketed devices• May require hand soldering for soldered devices



Key Messages….

J-STD-075 documents a process for managing Process Sensitive Components – Get it. Read it. Use it.

Demand Process Sensitivity ratings from your component suppliers (PSL).

Establish internal procedures to gather and use PSL data (board design, supplier selection, process definition).

Enforce component temperature exposure limits in all assembly manufacturing operations.– measure temperature exposure

– use alternate processes if necessary

….



Key Messages….

Do NOT depend on post-assembly functional yield to validate assembly of process sensitive components.

Be conscious of post-solder temperature sensitivities not adequately addressed by industry practice today.– gather supplier data; use it to ensure process compliance

Evaluate your finished products for temperature sensitivity in anticipated customer assembly operations—quantify limitations and provide to customer.

Expect future improvements to the industry specification framework for component process sensitivity.

managing temperature sensitive components in pb-free … · 2011-05-31 · components in pb-free...

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