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Solder wick on Ag/Pd termination

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#52133

Solder wick on Ag/Pd termination | 22 October, 2007

Hi, Recently we have encountered solder wicking on components termination (total of 13 pcs of components on one pcb)with Ag/Pd finishes during lead-free reflow soldering. The pcb is LF HASL surface finish and LF solder paste composition is SAC305.We tried to increase the solder paste thickness & prolong the soaking time BUT solder wick did happen again. Then we change to Ag/Ni/Sn termination component,we got a good solder fillets. Can anyone tell us what is happening ?

Thks

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#52140

Solder wick on Ag/Pd termination | 22 October, 2007

You say, "we have encountered solder wicking on components ..." We expect to see wicking on solder connections. Maybe we're just using different terminology. Please describe the problem that you're seeing.

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#52147

Solder wick on Ag/Pd termination | 22 October, 2007

Hi Dave,

The solder has tended to wet the component termination of Ag/Pd (chip capacitor) but has not wetted the pads, whereas the solder has wetted both termination & pads when using Ag/Ni/Sn finishes.

Thks

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#52148

Solder wick on Ag/Pd termination | 22 October, 2007

Double check on this, but we have this little voice in our heads telling us that your AgPd termination is intended for conductive adhesive applications. Check with your component supplier. We recall a thread on SMTnet [ http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=49101 ] not too long ago, where the complaint was maybe poor solderability of the component [not what you're seeing].

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#52150

Solder wick on Ag/Pd termination | 23 October, 2007

Thanks Dave. But I do not understand why the solder being wicking away by the component itself. Does Ag/Pd finishes has stronger wettability than LF HASL finishes ?

Rgds

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#52151

Solder wick on Ag/Pd termination | 23 October, 2007

We're not really sure. Usually when solder leaves the pads and wicks-up a component lead, it means the component lead is much warmer than the pad on the board. This is the direction we would have taken this if we hadn't taken the AgPd / conductive epoxy tact.

Thermal conductivity [W/m-�C] * Silver: 418 * Tin: 73 * SAC: 73 * Palladium: 72

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