pcb design & process challenges...pcb design trends • topography: – overall miniaturization,...
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PCB Design & Process Challenges
PCB Design Trends
• Topography: – Overall miniaturization, smaller components placed closer together.
– Overall PCB footprint reduction.
– Reduced PCB footprints, drive test-pad size and spacing reductions.
– 39m and 50m center-line test-points are common.
– Test-pad diameters: .020 and below.
– Dual sided test is common place.
– Thinner PCB’s.
• Manufacturing Process:– Lead Free Solder
– No Clean
– 0SP
Challenges:Today’s PCB trends:
• Topography:– Overall miniaturization,
smaller components placed closer together.
– Overall PCB footprint reduction.
– Reduced PCB footprints, drive test-pad size and spacing reductions.
– 39m and 50m center-line test-points are common.
– Test-pad diameters: .020 and below.
– Dual sided test is common place.
– Thinner PCB’s.
• Less area for UUT constraints. Damage due to placement errors is high.
• Fixture milling requires more precession.
• Technology to test small tightly spaced test-pads is required.
• Need to test thinner boards without inducing damage.
• Fixture design needs to be quantified before fabrication.
• DFT tools required early in process.
Challenges: Today’s PCB Process Trends:
• Manufacturing Process:– Lead Free Solder
– No Clean
– 0SP
• Brittle solder, UUT flex could fracture solder joints.
• Lead free solder is harder than its lead counterpart. Higher probe forces are required. Higher initial pre-loads required.
• Lead Free solder flux leaves behind hard sticky resins.
• Residue from no-clean difficult to penetrate.
• OSP, contamination and penetration issues.
Statistical Models
Figure (1)
False Failure Rate vs. Target Size
0
25
50
75
100
125
0.017 0.018 0.019 0.020 0.021 0.022 0.023 0.024 0.025 0.026 0.027 0.028 0.029 0.030 0.031 0.032 0.033 0.034 0.035
Pad Diameter (in)
Fals
e F
ailu
re R
ate
(P
PM
)
Conventional Recept Align Plate Guided Probe - Sm Guided Probe - Diamond TP EC-1
Guided Probe & Zeroflex.
Automated Board Processing Automated Stop Finger Placement
User will specify
clearance values.
Accommodates
the arcing motion
of the gate.
Sometimes the entire UUT will
be contained in a relief mill.
This information defaults to information provided by SMARTCAP
Automated Board Processing Real time DRC for fixture
Red hatched squares indicate
the probability of unacceptable
board stress levels.
Try lowering the spring force
of the probes in these regions.
Push Finger UUT Hard Stop
Board Stress AnalysisStrain Gauge Analysis.
CAD & BOM Merged
ECT’s “Quick Six” Bullets for Attacking PBFree in Test:
1. New Proprietary Plating: 550-650 Knoop vs. 130-200 Knoop hardness to resist abrasion, and less porous to resist solder (contamination) transfer.
2. Improved Spring Rate: Higher pre-load with the same force at test height results in improved initial penetration upon fixture actuation.
3. Spring Force Selection: 6oz – 12oz for effective penetration.
4. Bias Ball Design: Lower average resistance, lower standard CRES deviations, and higher current carrying capacity.
5. Double Roll Close: Optimal pointing accuracy.
6. Wide Selection Tips: 6- .050” tips, 6- .075” tips, and 10- .100” tips
(widest selection of lead-free, no-clean, or OSP products on the market!!!)