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SMT electronics assembly manufacturing forum.


solder strength

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dougs

#36485

solder strength | 2 September, 2005

Is there a standard that we should aim for in respect to the strenght of the solder on SMT leads? We have a customer who are testing our product by pulling leads off of pads then returning them.

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#36487

solder strength | 2 September, 2005

From Ray P. Prasad's article in this month's SMT magazine about the new IPC-7095 revison:

".....IPC does not have pull tests in any of its standards, and some reliability experts would prefer to keep it that way, pull tests are commonly used by some leading companies. Much data collection and rigorous analysis has gone into this technique, and it has been found to be stable and capable. We will provide some details about pull-test methodology in this document for companies that may want to use pull tests."

Article Link:

http://smt.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_ID=234562

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#36488

solder strength | 2 September, 2005

Just to be clear, Pete C is referring to the August 2005 SMT Magazine.

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#36489

solder strength | 2 September, 2005

Dougs: What is the purpose of this test?

Lately, we have had a lot of boards that do not withstand the Drive-Over The Board With A UPS Truck Test. We wonder is the is some relation between our test failures and your customer's.

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Rob

#36490

solder strength | 2 September, 2005

We used to see that a lot with securicor before DHL bought them. They used to tape up the boxes again with brown tape & pretend nothing had happened. We even had tire marks on one box.

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dougs

#36491

solder strength | 2 September, 2005

you tell me, the customer has started to pull at some of the leads of some IC's with tweezers while de-bugging boards that had failed in the field, he was able to pull some of the leads away from the solder joints, we feel he may be over-doing it a bit but are unsure about what the standards are. My feeling is that the joint should in most cases be stronger than the bond between the board and the pad but even still, we think the customer may be being a bit over zealous in his tests.

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#36492

solder strength | 2 September, 2005

Thanks Dave. Its September already !!

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Mity-C

#36493

solder strength | 2 September, 2005

We had a customer who came in to discuss a solder adheasion problem on some sub-assemblies we were building for them. When they arrived, they put a sub assembly in a vise and hit it with a hammer.

I was speechless to say the least......

C

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Rob

#36495

solder strength | 2 September, 2005

One of our customers picked up an assembly, dropped it on a concrete floor, then kicked it down the corridor. Broke his toe on the steel enclosure, & suffice to say never tried it again.

Nothing like decent, documented & controlled scientific testing.

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#36513

solder strength | 6 September, 2005

I love these stories.

At my previous employer we experienced intermittent failures on an audio microprocessor assembly being used on a *new* product. This board had numerous microprocessors and complex firmware aboard.

They discovered one PLCC on one board that had failed had a couple of obviously cracked solder joints and decided the fault was in the refolw soldering. Even the president of the company emailed me and said "I pried on one of the boards that you guys made and the solder joints seemed a lot weaker than those on a cheap Asian consumer product board", on a part that was "similar".

I never got to see the "similar" part, but our board had shattered 0805 caps on it where they had been used as a fulcrum for a screwdriver to pry off the PLCC.

$2500 worth of thin section analysis later they finally admitted it was a firmware problem. The leads on the PLCC cracked when it was installed into a too-tight card rack in the case and the assemblers decided to flex it into position.

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Slaine

#36526

solder strength | 7 September, 2005

i worked for a mobile phone base station manufacturer a few years back and they had a customer in Thiland who were complaing the cabinets we sent them were dented and marked, we investigated, improved packing and goods out inspection but still had the same complaints so , a college flew out to the customer to see the problems on site. whilst he was there he watched them unload a delivery of them, by pushing them out of the back of a wagon and roling them end over end into the warehouse. these are 2x.75x.75meters and �50,000 each.

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URL

#36534

solder strength | 7 September, 2005

We've seen the same thing - leads of QFPs not as strong as we'd like them to be. In the past 4 years no problem, this Spring they start failing. Touch a solder iron to it and it solders fine. After crunching some data, we found that both QFPs failing were manufactured at the same place. Looking at the part, they looked no-lead. Reviewed their data and found they went to silver immersion (although the sales guy swears they are leaded).

LSS, reprofiled these boards and found that the problem went away. This may your problem as well.

I agree that solder should only be used to make electrical connections, but in reality their is a mechanical bond as well (for reflow anyway). Sometimes the only way to assure there is a solder joint is to physically "touch" the joint. I'm not a big fan of it cause some people get carried away with it, but done under the right conditions, it can prove valuable.

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Slaine

#36537

solder strength | 7 September, 2005

an X-ray fluroscope XRF will tell u if there is any lead in it in seconds, without damaging it.

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URL

#36564

solder strength | 8 September, 2005

You're right, but my neighbor borrowed my X-ray fluoroscope XRF and never brought it back!

Actually, I just read the spec sheet which told me it was tin/silver leads.

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kris

#36566

solder strength | 8 September, 2005

what did you reprofile to ? did you increase the peak reflow temperature ? can you tell form what to where ?

I bet your vendor told you process guys that it was " drop in" for a tin leaded plated part.

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dougs

#36571

solder strength | 9 September, 2005

we've found the problem, our MD went to visit the company and their tech showed him a failed unit, it wasn't one we made.

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Rob

#36573

solder strength | 9 September, 2005

Strange that - whenever we take on a new customer & agree to work together in a spirit of partnership they invariably try returning all of their old failures, often with our labels hastily re-stuck over them.

We often change the copper ever so slightly or something on the silkscreen that the customer will never notice so we can spot one of ours if it (perish the thought) ever came back.

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