Poor solderability

Hi Russ, yes, I did get the homeplate info, thanks. Thought that it looks that way, only didn�t know how to deal with that expression. Now your problem: it�s hard to tell without seeing it actually. All I wonder is this 80sec above liquidous, at what speed are you running and what does that mean for your preheat time and where on that board is that measured? Once activated the flux has its function abilities only over a fixed time ( about 2 to 21/2 minutes if my memory doesn�t fool me, better check that for your paste ). You probably regain oxides which mingle with your solder and form a somewhat weak compound. With the weakest (smallest) joints (typicall the finepitch leads) you will than notice the easiest peel off. That�s something I noticed a couple of years ago happening during rework of QFPs with hot air performed with really bad profiles and the powerful blowing of oxygen into the solderspots. For the wave: best way to judge on prehaet is to measure the temp. at the top of the PCB. It should be higher for no clean (about 120�C) than for others when the PCB enters the wave ( of course the fluids should be dried out ). For specific temb. better ask your Flux supplier.

sorry for not beeing of more help

Wolfgang

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Russ: Now that�s a good story. Nuff said on the Vegas trip, that explains everything. Especially when you say "it must have something to do with ..."

I love WS609. It�s been berry, berry good to me.

Intermetalic Layer (IL). A compound formed at the interface of two different metals, whose atoms have an extremely high natural attraction for each other, so high, that they do not bond to other elements by any other means. Also, intermetalic compounds have fixed stoichiometric ratios. Whereas, alloys can have varying ratios of metals.

In soldering, a little IL is good. A lot of IL is bad. Yes, you could have the latter. There are 80 some messages on SMTnet on ILs. If you want more, I got it, but first ...

See, the whole electroplated gold to HASL conversion seems fairly ill advised. It�s a little bit tough to figure-out what happened, because you have such a goofy solder connection. So, tell me: * What do you see, when you look at the pad of one of these poorly soldered connections? * What's the story on reworking the boards? How thick was the electroplated gold? How thick was the nickel under it? What did they do those coatings before they added the HASL?

And you thought that story was enough for me ...

Dave F

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Russ - I agree with the other guys that the problem could be black pad or some intermetallic problem, possibly related to the "conversion" to HASL finish. But my first guess is still partial reflow at wave soldering. You won't catch it by pushing on parts during soldering, because the problem involves only a partial melting of topside solder joints. Also, it's so transient that it's hard to pick up by standard thermal profiling. It's most common on fine pitch leads (and BGAs), and usually only on pads that have a short trace going straight to a via. The via provides a path for excessive heat to be transferred to the topside lead. The classic symptom is when the affected leads break loose easily, and most or all the solder stays with the lead. You can probably find more information on this (and black pad)in the archives. A quick test is to use Kapton tape to cover the vias on the back side. This almost always provides a "quick fix" unless your solder dwell time is really excessive. Good luck. Glenn Robertson

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