Construction of electronic systemsC.Bohm

 Components + connections

 2-pole (resistors), 3-pole (transistors)4-pole (transformers)+..+10-pole vacuum tubes)

  

 First one used components mounted on isolating cards, connected by soldered connections

John Pinkerton

Increased component density demanded other methods Integrated circuits + single or double sided circuit boardsDIL (dual in line) packages wire wrapped circuit boardsHole mounted <30 legs

 

  

wrapped circuit boards printed circuit boards   

  

crossing leads problems with single sided boards (can be solved by jumpers)

  You can use vias on double sided boards (metal deposited holes usually 0.2-1 mm) 

 

DIL

 LSI (large) ic-circuits + multi layer boardsLarge DIL <100 legs many routing layersPGA (pin grid array) better <350 legs  

 

 

PGA

Special power planes supply power to the components

Active component

Long connections have inductance

Varying current transport

“Ground bounce”

Power plane with low inductance

Nearby decoupling capacitorsDeliver charges that can supply the current transientsThey work like energy reservoirs

Ground plane with low inductance Ground and power plane have also good shielding properties

Low frequentSignal current

Return current

Minimizeresistance

Minimizeinductance

Return currentHigh frequentSignal current

A cut in the ground plane forces the return current to deviatewhich affects the signal quality

A cut in the ground plane can also increasethe cross talk between nearby signals

Micro strip Stripline

Wide trace and small distance gives a largecapacitance – difficult to drive

Circuit board materials:FR4 (flame retardent 4)Roger (brand name) high speedPoly imide (Kapton) – flexfoïls

Rigid flex = combination FR4-Flex foil

Multi layer boards allows blind and covered vias

 Surface mounting usually < 10 layersHigher densities trace widths >0.1mm vias > 0.25mm 

 

SO PQFP BGA≤28 legs <400 legs <600 legs

>0.5 mm/leg >0.4mm/leg 1.27mm/leg

blind

dold

Vias through power planes Via to powerplane

Drop via Thermal via to simplifysoldering

Sufficiently large diameterto matchThe drill tolerance

Usually <10 layersTrace widths>0.1 mmIsolations distance>0.1 mmVias>0.25 mm dia

blind

covered

Thruhole

micro BGA, CSP <2000 <1mm/leg

Difficult to extract the signals between the balls

Many layers are needed

Alternative: use laser drilled thin micro via layers which

supports very thin traces

Pictures from elektrotryck.se

Pictures from elektrotryck.se

Laser drilled vias

Step#1 Film Generation:

Generated from your design files, we create an exact film representation of your design. We will create one film per layer.

Step#2 Shear Raw Material:

Industry standard 0.059" thick, copper clad, two sides. Panels will be sheared to accommodate many boards.

Step#3 Drill Holes:

Using NC machines and carbide drills.

Step#4 Electroless Copper:

Apply thin copper deposit in hole barrels.

From PCBpro.com

Step#5 Apply Image:

Apply photosensitive dryfilm (plate resist) to panel. Use light source and film to expose panel. Develop selected areas from panel.

Step#6 Pattern Plate:

Electrochemical process to build copper in the holes and on the trace area. Apply tin to surface.

Step#7 Strip & Etch:

Remove dryfilm, then etch exposed copper. The tin protects the copper circuitry from being etched.

Step#8 Solder mask:

Apply solder mask area to entire board with the exception of solder pads.

From PCBpro.com

Step#9 Solder coat:

Apply solder to pads by immersing into tank of solder. Hot air knives level the solder when removed from the tank.

Step#10 Nomenclature:

Apply white letter marking using screen printing process

Step#11 Fabrication:

Route the perimeter of the board using NC equipment

From PCBpro.com

PCB manufacture ·      PCB laminate about 0.2mm – different types: FR4, Polyimide (Kapton) and Roger·      drill·      electrolytic plating of holes– connect a voltage source to the two sides while in a bath·      add photo resist·      illuminate pattern·      rinse·      etch·      build the layer chemically·      glue several layer·      component print·      lack layer·      test with beds of nails or flying probes

Mounting components

Hole mounting ·      mount components·      wave soldering·      test Surface mounting ·      solder mask·      spread solder paste·      mount components (with robot)·      heat in oven·      next side·      test  

Circuit board data

generate pattern for the different layers – artwork

generate drill files

Control files to milling machine (to separate and shape the boards) 

Different layers

Cupper pattern

Component print

Lack layer

Solder mask 

Different physical layers (artwork order)

1 signal_1 pad_1

2 power_1

3 power_2

4 signal_2 pad_2

Start by creating a schematic 

Decide board size – shape, silkscreen print, mounting holes, placing and routing zones

Make sure there is a pattern for each component – pads, holes, vias and component print 

connect schematic symbols with legs to component pattern with pads

package circuit board data – translate schematics with symbols to component pattern and net list

place components on the board (side, position, orientation, ref nr) – manual, automatic or combined

draw traces in the connection layer (with support from schematics) – manual, automatic or combined –

different trace which gives different impedances

split ground plane – avoid couplings between analogue and digital parts

area fills – fill empty areas with grounded cupper surfaces

Soldering 

Soldering in solder oven:

 Temperature profile

  Solder quality

  Inferior wetting depend on poor heating or insufficient amount of flux

Lead free solder enforced in industry – higher temperatures

Conductive glue is sometimes an alternative

OK

För lite lödtenn

Dålig vätning

Not enough solder

Insufficient wetting

OK

Double sided mountingdifficult

ESD-protection ESD = Electrostatic Discharge

ESD floors (ground conductive floors)ESD shoes (ground feet against floors)ESD wrist band (grounds arm against table top)

time

Fai

lure

rat

e

Burn-in

ESD damage

At 50% humidity the human discharges rarely produce more than 2000VAt 5% they can easily reach 15000V

Inputs are often protected by diodes

Bath tub curveBurn-in

 Accelerated aging at elevated temperatures

Shaking to provoke cold solder joints

Thermal cycling