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De-wetting on Immersion Silver finish board

Murad Kurwa


De-wetting on Immersion Silver finish board | 24 August, 2000

One of our divisions is having this problem:

- De-wetting on the smt pads and componenent termination on the bottom side after top side procssed through reflow. Board finish is immersion silver.

? Any recommendation on what we should check & verify * Problem is random in nature. Not component related * De-wetting only on the bottom side after top side reflow * De-wetting only on chip components/pads * There are vias on pads but the problem is not correlated with these pads * No apparent contamination on the pads * Have not verified the immersion silver thickness

Thanks for your help. Murad

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Re: De-wetting on Immersion Silver finish board | 25 August, 2000

Hi Murad,

like with many other questions it�s hard to judge without seeing the effect. Assuming that this site you�re talking about is well equiped with knowledge and that they handle their processes normally to everybody�s satisfaction it�s obvious to look at the one thing that has changed, therefore focussing on the boardfinish would be the first thing (testing of solderability, checking for contamination and all that stuff). Although there�re publications on that specific finish with the tenor that there�s no problem with it I encountered similar problems and it was said that the board house had some problems adjusting the parameters for the (for them) new process and this should soon be better we decided not to go with that finish. If you decide to change one parameter in your process ( like in this case changing the finish ), do it carefully on a small scale (batch). Examine the effects on processes and products thoroughly before you go with it. You are well advised working as closely as possible together with the board house so that in the end you get what you need. It might turn out that processes have to be changed slightly, more care in handling (cleanliness required) or different fluxes are needed etc. So go for the large scale run only when you are sure it works.

It sounds rather theoretical but electronics are no lottery and if someone states something have him to proof it to you.

Good luck Wolfgang

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