Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Open joints

Claude Tremblay

#17764

Open joints | 3 October, 2001

Hello everyone

We have a QFP-308 (0.20" pitch)on a board and we have a lot of opens after reflow. We checked our profil by installing thermocouples on the pads of the component and everythings seems OK. We checked the coplanarity of the leads and it seems OK too. We noticed that the pads width are at the edge of acceptability (0.010" according to IPC-SM-782) and the board as a poor HASL.Pads are not all at the same height.Also I have solder mask between the pads.

Those things migth be the cause of the problem or maybe not. Does anybody experienced the same problem?

Thanks

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#17767

Open joints | 3 October, 2001

When we found this to be a problem with some QFP 100's (.020" pitch, and our first experience with fine pitch - 48 of them on a 2-up panel), we saw that the solder was running up the leads during reflow and staying there, leaving the fillets thin or nonexistant. We use HASL also, although we don't feel as though it's a big problem.

We monkeyed with the profile too, and it helped slightly, but eventually we determined the problem was a stencil design that had lousy release characteristics and even worse registration on our manual printer. We got a better printer, a new stencil, and the problem was gone. Not the cheapest fix, granted, but affective.

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#17770

Open joints | 3 October, 2001

We have had soldering problems with fine pitch QFP in the past [and probably will in the future]. Several questions leap to mind: * When you took your profile on the component pads, do you profile on the pads that did not solder well? * When you say the profile seemed OK, what were the numbers? * What is the solder paste that you use on this board? * What is your process up to the point of recognizing the problem we�re discussing? * How did other pads on the board solder? I assume everything soldered GREAT, except this fine pitch part. * Continuing with that thought, when you say �and the board as a poor HASL�, what specifically are your complaints with the solderability protection? * How do the leads on the fine pitch part solder when using a soldering iron? Or touching-up the connections on the board? * As Steve says, where is the paste going after reflow? * Continuing, what does the �open connection� pads look like [i.e., reddish-brown, silverfish, grayish, er what?] after reflow? * Is this a new problem with a new board? Old problem? New problem with an old board? Does this affect a single or multiple components / suppliers / etc?

Commenting: * Pad width of 0.010" on the fine pitch components should not be a problem. * Fine pitch components pad that are not all at the same height [length???] should not be a problem, providing they are roughly the same length and meet minimum requirements.

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#17771

Open joints | 3 October, 2001

No comment or intent to appear critical on your particular situation, because you did the troubleshooting to determine the source of the problem, but �solder on the component lead, but not on the pad� is more often caused by a reflow profile that gets the component leads much hotter than the component pads on the board [as you say] than making a printer sales person�s day. Although, it would be nice to have a new printer AND have that fix the problem. Pfew!!!

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Michael Parker

#17773

Open joints | 3 October, 2001

I hate it when that happens. Usually I just buy a better brand of papers. Zig Zag works best. Of course, you gotta remove the stems and seeds, those are the most recurring sources that cause an open joint.

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#17774

Open joints | 3 October, 2001

A firm grasp on the sublime. Mike points-out a good reason to describe Claude's problem as "open connections" or "open solder connections"? [Ahhh geez, wut a spoil spurt]

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vance

#17775

Open joints | 4 October, 2001

Overwetting is also a root cause of open joints. I recommend eating 5 saltines in 1 minute for anyone experiencing overwetting.

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