Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Sn plated

yukim

#24125

Sn plated | 13 April, 2003

Hi, We are placing (+) & (-) terminals in SMT. We have just changed the plating of them: from Nickel to Tin (Sn). During the trial, we used the same reflow profile as before changing, and the solder seems different: a bit cold, with some solder paste particles on topside of the terminal. What should the reflow profile look like? Should be expect any other problem? Thanks, Yu.

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yukim

#24126

Sn plated | 13 April, 2003

Just some more info: PCB is HAL finished we are using Sn63 solder paste.

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#24133

Sn plated | 14 April, 2003

Consider: * Sn has a higher melting point than Pb. So the liquidous temperature of this new, non-Sn63 is going to be higher than 183*C. What was the thermal recipe measured on this solder connection? * Next thing we'd do is take problem devices and turn them upside down (i.e., "dead-bug" position) and measure the plating thickness and composition using xray fluorescence. Soldering problems with high tin content plating usually is an indication that the leads weren't plated correctly. If the plating on the leads isn't above 200 uin you'll probably have soldering problems.

We doubt that you are talking about this, but the appearance of your solder connection could look different, because your have a different metal alloy than previously. This in itself is not a basis for rejection.

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yukim

#24175

Sn plated | 16 April, 2003

Hi Dave, thanks!

The peak temp on the terminal device is about 210C. Some more questions: The soldering part of the terminal is about the same size as the PCB pad. We observe a lot of voids when we remove the terminal device, whice can be removed very easily. Both PCB pad finish and terminal plating finish are not perfect, I do not think the voids are due to those imperfections. Could they be formed during the reflow, because the plating is removed and there is any chemical reaction? Hope I am clear enough. Thanks, Yu.

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#24178

Sn plated | 17 April, 2003

First thing to try is get the solder connection hotter. 210*C is just not warm enough for the 'high' tin content of this connection.

Second, it's disconcerning that you don't have good plating on the pad or the terminal. Why can't your board supplier do a good job with HASL? Why are you using boards like that? ditto the terminal.

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