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cold joint on 1 lead of IC

Views: 1604


tjc

#47380

cold joint on 1 lead of IC | 8 February, 2007

I have received 10 customer returns for a cold solder joint on 1 lead of a 36 pin IC. Everytime it is on the #18 pin. The process is reflow and I can't figure out why the one leg is cold and the other legs look OK.

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#47381

cold joint on 1 lead of IC | 8 February, 2007

tjc,

Is this pin connected to a heavy conductor or ground plane?

Chris

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#47384

cold joint on 1 lead of IC | 8 February, 2007

Most likely ground plane stealing your heat. Increase dwell slightly if you can.

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#47385

cold joint on 1 lead of IC | 8 February, 2007

groundplane not heating properly..

Is it a J leaded IC? sometimes these get bent slightly in the packaging and sit just far enough off the board to cause solder problems.

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SWAG

#47387

cold joint on 1 lead of IC | 8 February, 2007

Check the bare board - could also be an unmasked via on the heel of the pad that is sucking solder into it.

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#47390

cold joint on 1 lead of IC | 8 February, 2007

Got a picture? Most times I hear this situation it turns out to be a bent leg on a thru-hole transistor that didn't go through the board.

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#47413

cold joint on 1 lead of IC | 8 February, 2007

What is the measured temperature on: * Pin 1 * Pin 18

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#47559

cold joint on 1 lead of IC | 12 February, 2007

A little late to the party here, sorry...

Has the joint been verified as a cold solder joint? That is, visually confirmed that it looks like cold solder, and, perhaps, xrayed to confirm the solder status?

X-raying may sound a bit extreme, but you've had a customer return 10 assemblies for the same failure. It's been my experience that cold solder is very difficult to diagnose simply by testing/inspecting the joint. Especially if it's a RoHS assembly, were the joints tend to look cold by tin-lead solder standards.

A number of people will tell you that you can confirm a cold joint by re-flowing it, and re-testing. If it passes, the solder joint must have been cold. While this is a true statement, it's not necessarily always true. IC's the heat from the iron could cause an IC to temporarily work, and then go back to failing once it's cooled down.

So, the only way to begin root-cause investigation is to confirm the diagnosis of cold solder in the first place. Then you've got some jumping off points for your root-cause analysis.

cheers ..rob

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