Dear Patricia
I'm experienced in PCB fab and hope I can help.
First, let's correct a small terminology issue. The potential problem would be "Resin Smear" covering internal layers and causing a interconnect reliability problem. "Desmear" is the chemical orocess used by PCB suppliers to remove Smear before copper plating.
I'm not surprised you have a case of interconnect reliability related to large diameter holes since it is actually more difficult to drill large diameters with good surface finish than small holes.
So it is possible the parts were properly processed including Desmear but that the large diameter holes had more smear (often the case) and Desmear was not adequate to ensure good reliability for just this size.
To help diagnose this I suggest:
1. Run microsections comparing the via or smaller component holes and the large holes. If the via quality is good and large size not, it suggests a size-specific problem related to drilling QC.
2. Check the PCB fab production process flow. Are desmear and electroless plating combined in one process? This is usually true, and if so, it's impossible to miss the Desmesar step.
3. Does the supplier used "stepped hole coupons" (ie, one row of holes, one hole of each size in order) to spot check quality? Is yes, check some. If not, suggest they add this to the panel design.
4. Due to the inherent problems with large holes, IPC suggests the design practice of adding smaller diameter vias to redundantly interconnect. Is this can be added to the design it provides safety margin.
Hope this helps.
Regards,
C.B. Katzko
Research + Development
Meadville Group
by Blackberry
----- Original Message -----
From: Patricia Lui [[log in to unmask]]
Sent: 08/23/2009 11:00 AM ZE8
To: [log in to unmask]
Subject: Re: [TGAsia] 答复: [TGAsia] Holes Desmear I ssue
Dear Jason,
Our factory did all the necessary test and measurements, even with cross-sections but no problem found. This hole desmear issue only surface after assembly. It do not surface at bareboard level.
I was suspecting that the boards already have the desmear issue after assembly and if the assembled boards are checked using correct ICT with low resistance setting, these issues boards should be picked up. I really hope that someone who have encounter this sort of issue before or who have expertise in this area could give me some advise.
Thanks for your advise, I do agree that PCB manufacturer should produce boards with longlasting and good reliability, but we also need good sets of testing down the line.
Best Regards
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