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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


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Dewetting | 6 July, 2010

Hi all,

Recently, we found the IC lead dewetting as shown in the attached file..This problem only happen on particular lead only...We checked our reflow profile and its look everything is fine..We did cross section and EDX..I think this could be material related issue..What do you think by referring to this report?

Rgds, Sean


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Dewetting | 6 July, 2010


We can't comment on the EDX report; but, we have seen these types of problems before.

We would initially agree with you that it seems like a material issue. A solderability test should be performed on the part, and on the board. Easist way to do the board is to paste/reflow an empty board in the normal process, and check out the solder formation. Easiest way to check the part is to have the leads tinned, then solder to the board (while taking a non-tinned part, and also soldering to the board).

Beyond material finish issues, consider the planarity of the leads of the part. If the leads aren't relatively co-planar (I say relatively, since it's not a significantly fine-pitch device), it's possible that the leads are not sitting in the paste enough for reflow.

If planarity and solderability are not at issue, then my next guess would be thermal inbalance of the device layout. If the solder is not reflowing at a uniform rate in reflow, the component could be pulled in one direction, and lift the lead out of the solder.

cheers ..rob

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Dewetting | 7 July, 2010

Rob gave you very good analysis and suggestions for troubleshooting your non-wetting issue. We agree with his sequence of troubleshooting. The following comments are meant to be a line to supplement Rob's plan of attack.

This adds to Rob's comment about planarity. Some parts are planar before and after, but not during reflow. When these parts are not planar, they can lift a termination out of the solder before solder solidification. Test this on your part by: * Placing the part bug-up on a hot plate and increasing the temperature to reflow level and watching the part near the suspect lead during the thermal cycle [If there's a problem with the part, the part will be moving like a SoCal jumping bean] ... OR * Alternately, rotating the part on a test board and reflowing it [If there's a problem with the part, the site of the problem will move with the rotation]

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Dewetting | 8 July, 2010

Thanks Rob and Davef..

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Dewetting | 9 July, 2010

Hi Sean, I have seen this issue with lead free component on Sn-Pb solder process, I don´t know if it´s your case. Some times, pins not reach the necessary T for solder due to lead free metalization and in other case due to a groud pad, with a big T dissipation. take a look, Rafa,

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Plasma Prior to Conformal Coating