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"Gap" in completed solder joint between lead and pad

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Michael Sanders

#45715

"Gap" in completed solder joint between lead and pad | 28 November, 2006

Is anyone aware of any articles, white papers, etc., that discuss the gap between the lead and the pad after a SM joint is soldered? In particular, I am looking for a formula for that "gap" for various components.

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GS

#45716

| 28 November, 2006

Have you seen IPC-A-610 D ?

regards GS

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M. Sanders

#45722

"Gap" in completed solder joint between lead and pad | 28 November, 2006

Unfortunately, I don't have a copy of IPC-A-610 D on hand, however, I believe in IPC-610, this �floating height� between lead and pad has no maximum specification restriction. As long as there is no voiding, it is still acceptable for all 3 classes. My question is � is there a formula to calculate the possible �float height� � given the solder stencil, lead size, and paste thickness variation? We find the component to be lifted slightly (typically 0.02 � 0.3mm).

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#45723

| 28 November, 2006

Try IPC-SM-782.

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#45732

"Gap" in completed solder joint between lead and pad | 28 November, 2006

We don't have a gap between the lead and the pad after a SM joint is soldered. On our boards, this space is filled with the solder intended to attach the component to the board.

How high do components sit above the surface of a board? Most people answered 2-2.5 thou.

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M. Sanders

#45752

"Gap" in completed solder joint between lead and pad | 29 November, 2006

I'm sorry, Dave - I didn't make myself very clear. Yes, this space (not really a "gap") is filled with solid solder. For instance, if you place a gull-wing component in solder paste, after reflow, there will probably be a thin film of solidied solder between the lead and the pad. Judging from your comment, one would assume that to be 2-2.5 mils. One of our customers does not believe there should be any "space" between the bottom of the lead, and the pad(I guess they assume the component would displace all solder underneath the lead), so I'm looking for a white paper (with a formula to calculate this thin film for various components)to prove it to them.

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#45756

| 29 November, 2006

IPC 610 *C* states that the solder thickness requirement is a properly wetted termination is evident. Fillet height is another aspect and is usually specific to the package but is some function of solder thickness plus a percentage of lead height.

Don't have D, sorry.

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#45778

"Gap" in completed solder joint between lead and pad | 29 November, 2006

Your customer is so poorly educated that you should decline their work, because this will not be the last time they waste your time with their cockamamey theories.

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M. Sanders

#45825

"Gap" in completed solder joint between lead and pad | 30 November, 2006

Dave, Thanks - I couldn't agree with you more. Unfortunately, our "bean counters" have a different frame of mind.

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CK the Flip

#45826

| 30 November, 2006

Mike, dude, I feel your pain. Hearing stories like this makes my blood boil! It's almost as ridiculous as a customer who told me to put more solder paste on a MELF component to overcome noise issues - he used more solder paste as antennas to overcome his poor RF design.

Explain to your mentally retarded customer that solder is a conductor of electricity. It holds components in place between the component lead and the land of the printed circuit board. Electrons then flow through the solder, the circuit board, the component lead, and the "innards" of the component itself. Talk very, very, very slowly when explaining this to him.

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Hussman

#45827

| 30 November, 2006

Wow, why all the anger? This gap you guys are talking about is measured as "G" in IPC/EIA J-STD-001 (Chunks was there, but she failed to read the fine print). And almost all parts that measure G follow Note 3 which states "Properly wetted fillet shall be evident". This is manufacturing 101. If you plan to be in this business, know a little something about it. Don't expect your customer to know what he wants, cause he's looking to you engineers to be able to back anything you produce. Sure the customer may be poorly educated, but if they knew all about SMT manufacturing, why would they need you? If you�re not willing to jump thru a hoop for them every once in a while, they�ll go to someone who will. Jeez, if I turned down every customer that asked a dumb question I�d be out of business. When they ask for the impossible, show them why you cannot achieve it. But this is not an unreasonable question. And it can be answered quite easily by a novice engineer. Perhaps they�re putting their name on a product that your making making for them. ,Isn�t human nature for them to question everything? Wouldn�t you? Or at least want to look at some solder joints? Maybe their last CM f@cked up their product because of a related issue. You never know. What you should know is how to answer their questions with a little logic. And IPC sure makes it easy.

Ok, you can slam me now like you did your customers and bean counters, but if we didn�t have them we wouldn�t be needed either.

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#45828

| 30 November, 2006

Maybe ask your customer where they got this idea from? It is possible they may have even got this idea from some white paper or article where they are trying to explain something else and show drawings with no solder between the pad and lead. It may have solved some other problem for them so they think this is the duck's guts. Ask them where do they think this solder on the pad should go after reflow?

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Tim Gravit

#45834

it be screener | 30 November, 2006

u need 2 use dek printer

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#45855

| 1 December, 2006

You're right Hussman, I kinda missed the follow thru on that one! Sorry for any confusion on my part boys.

Huss, you going to APEX this year? We missed ya last year. L.A. this year....boo!

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