Electronics Forum | Wed Sep 16 00:03:55 EDT 2009 | linseeg
We encoutered few PCB after IR reflow the PCB pad change color from silver to yellowish / brownish. Our IR reflow peak temp is ~250 degree. The brownish cannot be remove with IPA as well. What is the main reason causing this issue?
Electronics Forum | Wed Sep 16 13:32:05 EDT 2009 | davef
Questions are: * What is the solderability protection on the pad that changes color? * What is the distribution of this issue?
Electronics Forum | Wed Sep 16 22:41:51 EDT 2009 | linseeg
PCB finishing is immersion white tin. The brownish is at random location at PCB pad. The issue only affect visual reject but no solderbility functional failure.
Electronics Forum | Sun Sep 27 11:41:13 EDT 2009 | rajeshwara
We are using ST Demodulator QFP in our product which have exposed pad / heatsink from bottom side. Visually or in magnifier the solder joint or fillet looks good but if we touch up the pins with soldering guns , PCB works fine.
Electronics Forum | Fri Oct 30 10:36:26 EDT 2009 | richie_puthotta
Hi, I see a huge solder mask shift on chip comp pads. This would result in mid-chip solder balls or solder beads. Overall, the solder mask workmanship is not acceptable. Mask is on pad.
Electronics Forum | Wed Feb 03 22:29:08 EST 2010 | mika
via apertures > solderding of terminals to the pads! That is zero which means => 90 % solderjoint Terminal to pad! http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=13914&#Message58952
Electronics Forum | Thu Aug 05 14:58:18 EDT 2010 | mikesewell
Smaller and multi-row QFNs will probably require an oblique view/5-axis xray with resolution of at least 1 micrometer and preferably a nanofocus machine. Given the low standoff and small pad size, verifying wetting can be challenging on interior pad
Electronics Forum | Thu Sep 02 03:00:59 EDT 2010 | sachu_70
Hi Kevm, would it help to try solderability test of these pads using an agressive flux during soldering? Just a thought.
Electronics Forum | Wed Sep 15 04:12:11 EDT 2010 | headlad
We had a similar problem so we shrunk the thermal and extended the pads. This allowed us to ensure solder resist was applied to the track in between. It fixed our problem.
Electronics Forum | Thu Sep 16 08:47:39 EDT 2010 | headlad
I extended the pads to help ensure the component locates correctly and to allow for easier re-work should problems occur. I reduced the thermal by 5% but you may want to speak to your fabricator and ask what they require to ensure that the resist is
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