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| Date: | Wed, 6 Sep 2017 13:42:58 +0000 |
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Speaking in broad strokes and generalizations...
A rough hole from drilling indicates a greater stress and nastiness introduced into the hole during drilling. That then suggests to the casual observer greater potential disruption to glass/resin bond. Those heating and tearing stresses from drilling can reduce strength of that material, increase potential for entrapped moisture and chemistries (and the wicking and CAF that can come with it), hole wall voids (and effects like you discuss, i.e. blowholes) and I suppose glass nodules that plate ugly.
The rougher the via, the more likely as it's aspect ratio increases it is to entrap debris from the drilling process and the more likely it is to have plating defects (rough hole wall = more challenge moving solution in and bubbles out).
Also, generally, the higher aspect ratio the hole, the less roughness it can tolerate and the shorter useful life the via will have. Roughness creates stress risers that copper cracks propagate from.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Deng RongJun
Sent: Wednesday, September 6, 2017 2:54 AM
To: [log in to unmask]
Subject: [TN] PCB hole wall Roughness
Fellow TechNetters:
IPC DR-572A 9.3.3 has defined that the maximum allowable roughness is recommended to be 25 ìm. Is this for all size drilled holes?
Sometimes I head from PCB fabricator that the drill hole roughness is depends on hole size, ex.: 0.5-0.8mm drill hole roughness <25.4 ìm, 0.8-2.6mm drill hole roughness <30 ìm.
The hole wall roughness will cause blow hole in solder joint during wave or selective soldering if moisture go in to PCB inside. So we need to control the roughness on hole wall surface.
Is anyone have experience on this? What roughness is reasonable for PCB hole?
Best regards
Deng
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