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Bump Dies Solder Integrity

Jeff Sanchez

#3524

Bump Dies Solder Integrity | 18 July, 2000

Hey all, My brother is a tech at TI. He is running tests on bump dies. The question is if he heats up a die (actual waffer) with out disrupting the solder can he still use the solder. Will the solder lose its integrity? Keep in mind that these bumps are way small. One of his engineers thinks the solder is useless after you expose it to heat. I don't think that's the case and my brother doesn't think so either. I am not totally sure of how the bumps are bonded but I think they use flux. My only concern is weather oxidation is an issue after heating it up once. Any and all feed back is welcome. Thanks all.........Jeff Sanchez

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JAX

#3525

Re: Bump Dies Solder Integrity | 18 July, 2000

Jeff, I would tend to agree but then again I am not an expert. Get in touch with technical support at following link. They will probably need a little more info but they should have an answer. Have Fun!

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#3526

Re: Bump Dies Solder Integrity | 18 July, 2000

Hey Bud: Thanks for the response the other day. We currently use "Jeff�s Method #2: The Drummel Tool."

Short answer to your brother is ... yes, probably.

Expanding a bit: � It would be surprising not to use a flux to help reflow the solder balls to pads on the wafer followed by cleaning. � You�re correct, heating will increase the oxidation on the surface of the solder balls, whether this limits the ability to form a solder connection ... yagot me. That depends on how much oxidation, activity of the flux, etc. � Routine heating will not change the basic alloy of the solder ball. Consider the tin / lead phase diagram (http://www.umist.ac.uk/~intmic/phase/pbsndiag.htm). As you heat (cool) the alloy, you move straight up (down) through the phases. The constituents of the alloy don�t change. Material would have to be added or subtracted to change the alloy. � Continuing with this line of thought, heating undoubtedly will increase the intermetallic layer thickness between the solder ball and the pad on the wafer, whether this: - Affects LT reliability ... yagot me. That depends on temperature, time, product application environment, etc. - Grows the IM layer so thick that it won�t solder is possible, but then the ball would have to be entirely converted to whatever IM forms between the solder and the pad materials that are used at TI. � One final point, engineers can be very tricky people, sometimes using words with shades of meaning that regular carbon based units don�t interpret well. So, I wouldn�t go to mattress on this until I well understood the engineer�s point of view.

Expanding on this to better understand your brother�s engineer�s thinking: If the engineer is thinking that there is flux mixed with the solder of the ball and that it will be burnt-off during the heating process, he is correct that the ball will be unsolderable without additional flux.

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