Lon,

What your PCB producer told you does not make sense. 

Although the tin-lead alloy might have different wetting performance on flash gold pads, it should not have non-wetting in any event. If the flash gold is still there after soldering process, you have solderability problem with the boards. X-ray inspection is not a solderability test. 

Liang Yin
Process Research Engineer

Unovis Solutions 



> Date: Fri, 9 Nov 2007 16:23:00 +0100
> From: [log in to unmask]
> Subject: [TN] non wetting
> To: [log in to unmask]
> 
> Dear Technetters,
> 
> We had two boards out of 25 with a nonwetting problem. After reflow there was no solder on the flashgolden pads. Instead all the solder had gone to the leads of the 0805 capacitor.
> 
> Our pcb producer comes with the following conclusion:
> 
>  	"Our Q-dept. just informed me that they did x-ray inspection of the 2  boards you sent us back recently. Apparently 	there have been components used which contain up to 20% lead. During reflow-soldering the tin-lead on those 	components will melt first and absorb all the solder paste even before the tin which is included in the solder paste 	will melt. A golden flashgold pad without any tin will be the result. The tin will accumulate on the components and 	create those solder-balls instead. 
> 
> 	In a second test we did lead-free soldering  on the side which contains no components. The two PCBs showed excellent 	tin-wetting on this side. All pads – big and small ones – are nicely covered with tin. So basically we will reject 	any complaint - the boards are ok."
> 
> 
> Does this make sense?
> 
> Regards,
> 
> Lon Weffers
> 
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