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SMT electronics assembly manufacturing forum.


Solder Joint Strength Comparison

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#51642

Solder Joint Strength Comparison | 4 September, 2007

How do other people check their solder joint strength after a process change? For example, say you are getting wetting problems and you feel that a change to the reflow profile may help, or perhaps a slight change to the stencil aperture to reduce solder balls is to be tested. The fault level is very low and you would have to run extended trials 50,000 PCB's (several days worth of product)to see if you had made an improvement. But you would also like to make sure that you haven't weakened the solder joint and potentially made 50,000 scrap boards. To keep yourself right you would like to compare the joint strength before and after the change, how could you do this quickly, without the need for weeks of thermal cycling, but still getting some hard data behind it. I've read alot of threads about the cons of Shear testing, but in this case would it be a valid test? If so can anyone recommend a small handheld device to do this. If not how else could this be done?

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#51646

Solder Joint Strength Comparison | 4 September, 2007

Honestly, I inspect the wetting and the solder volume.

I leave mechanical testing to the CEO types that pry on components with screwdrivers and tell you it feels weaker than he thinks it should.

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#51657

Solder Joint Strength Comparison | 5 September, 2007

Hi Lloyd (did I just stutter?),

While I do love Steve's response, I must add that solder is not a very strong metal. And technically, it's sole purpose is to provide an electrical connection. It's a bad choice for mechanical connections, yet everyone thinks it should hold up to pry bars and screw drivers. Now if I were you, I'd would do a visual inspection before and after your stencil changes and compare to IPC specs. Use a Hi-Scope to inspect with or send out samples to a Trace Labs. Well worth the cost of scrapping 50K boards.

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#51658

Solder Joint Strength Comparison | 5 September, 2007

One of our customers does a drop test. They hold the final unit five feet above a concrete floor and drop it.

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#51659

Solder Joint Strength Comparison | 5 September, 2007

When I worked for a med. device company it was always great fun to observe the UL testing. Everyone would gather around the stairwell and say bon voyage to an $8k piece of gear.

This was NOT a test of the mechanical strength of soldered connections, however.

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#51663

Solder Joint Strength Comparison | 5 September, 2007

While I agree with Realchunks, the joints do have to at least have to hold the parts on the board. So your test might have had another purpose but it would also be testing if they had enough mechanical strength to hold the components on. Drop an unreflowed product, and then tell me it didn't demonstrate that the joints weren't strong enough to hold parts on.

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#51664

Solder Joint Strength Comparison | 5 September, 2007

What's sad is, it really happened. I won't bore you with the details again. ;)

Lloyd, I would love to have a nice Hi Scope too (I think Cchunks works for one of those big champagne and caviar corporate entities ;)) but if you can't swing it, at least try to get a zoom scope that'll do at least 10x-40x and a good fiber optic light. With that you'll know pretty much everything you need to know about the quality of your visible solder joints. If they're wetting right, you'll see it, and if they're wetting right, the only way you're going to get stronger joints is to put more solder down (thicker stencil). Of course that just brings along it's own baggage.

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#51665

Solder Joint Strength Comparison | 5 September, 2007

LOL! Well I do make the BIG bucks - 8.5 by 11 in size, but our Hi-Scope is the same one Abe Lincoln used in the Civil War. It's old, but does the job. I've had my share of Q.E.s using every thing imaginable to mechanically test the solder. Although if you fill their little heads with "latent failure" theories, and how their testing could cause field failures, they tend to be easier with the crowbar.

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#51680

Solder Joint Strength Comparison | 6 September, 2007

"...but it would also be testing if they had enough mechanical strength to hold the components on."

Only if you take the time to observe the results. :) Your point is well taken, but these guys were only interested in seeing if any failure modes promoted electrocution.

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#51722

Solder Joint Strength Comparison | 10 September, 2007

One of our customers bangs the assembly on his table top to see if parts will fall off. Darwin is alive and well in the OEM world...

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#51732

Solder Joint Strength Comparison | 11 September, 2007

Does he look at the board under a Mantus and mistake vias for solder balls, get mad and walk away? Mine does.

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