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SMT electronics assembly manufacturing forum.


Conductive contamination and the elusive solution

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#51012

Conductive contamination and the elusive solution | 12 July, 2007

I'm new to the website so if I don't sound like I know what I'm talking about I probably don't. But I am having a great problem at work with conductive contamination that bridges two leads and shorts out the IC, causint costly repair. I have been told the contamination here is worse (as in occurs more often) than many other places, by some of the more experienced people I work with. We have a vacuum system in place that is supposed to solve this problem and suck up any loose particles, and have implemented new cleaning strategies throughout the line, but nothing seems to really work. The machinery we use is pretty old (close to 10 years), not sure if this has anything to do with it. I was hoping maybe somebody has run into this problem before and came up with the miracle solution to make it go away, if so please please share with me. Thank you for all replies in advance. Scott

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#51013

Conductive contamination and the elusive solution | 12 July, 2007

Hi Scott,

Hard to tell what kind of problem you really have. I guess you need to describe your process first. What kind of process are you using. Wave solder, reflow solder, etc.. What kind of flux are you using to solder with? Vaccum? What are you vaccuming? Also, if you can give us a picture of the contamination, that would speak volumes. You can't show pictures here, so how about a common site we can view picture or two.

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#51015

Conductive contamination and the elusive solution | 12 July, 2007

Canyou see this contamination? Is it solder beads, flux or something else? If flux, then more cleaning should help, either more time, more cycles through the cleaner, etc.

If it is solder beads that are not melted to the rest of the solder, then something more aggressive is needed. A higher pressure spray, brushes, etc.

If it is an invisible residue, then your cleaning method is not working right, ie. the solvent may have flux residue building up in it. When the board dries, the remaining contaminants are left as a thin film all over the board.

Jon

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#51016

Conductive contamination and the elusive solution | 12 July, 2007

Are you talking about problems with your product or your SMT/wave solder equipment?

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#51023

Conductive contamination and the elusive solution | 13 July, 2007

Sorry I have just started working in this industry so I am not as familiar with everything. The probelm is with the Product shorting because of small pieces of metal stretching accross two leads of an IC. This could be a result of faulty equipment? or....I'm not sure honestly where the problem actually lies. Sometimes it is a piece of solder, sometimes flux, sometimes even stainless steel that is only 7 micrometers thick but about 200 micrometers long, there are also cases of aluminum and copper. To answer the question about being able to see it, no you can not see it with the naked eye, a microscope is usually necessary. We use a screen printer then reflow for some soldering and a solder wave for other parts. Has anyone else had a problem like this?

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#51024

Conductive contamination and the elusive solution | 13 July, 2007

wow, never heard of such a thing! Are you sure it's allways different types of material? Are you using a washer that isnt cleaned regular? I would check your product step by step, from bare PCB to finished product to find out where exactly in your process this happens.

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#51027

Conductive contamination and the elusive solution | 13 July, 2007

Just starting and already responsible for product quality and machine adjustment? Wow, you poor bastard. Ok, I will assume this problem happens on the bottom side of the board with a thru-hole IC. The short occurs on the side that doesn't have the plastic body of the part. Small micro-shorts are probably caused by not enough flux. Assure you are fluxing the board properly thru fluxer adjustment. I bet your operator knows how to this, or make a call to your machine manufacturer. Large solder shorts could be caused wave height too high, no mask between leads, lead length too long, conveyor being too fast, again not enough flux, poor preheat, poor board design..... etc. Like I said earlier - you poor bastard.

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#51034

Conductive contamination and the elusive solution | 13 July, 2007

The Contamination has proven to be pretty random, lots of stainless steel though in fact two cases in the past two days. As far as I know all machinery is cleaned regularly as well, even the stencil washer itself.

The boards we make are 90% (at least) Surface Mount Components, with maybe 2 or 3 through hole components. The contamination sometimes lays on top of the IC leads, sometimes is behind them where it is extra hard to see. Thanks for the input about the solder wave and flux spray. When solder contamination is the case I will be sure to keep that in mind.

Has anyone had problems similar to these? or Does anyone have a process at their plant that is supposed to ensure board cleanliness that actually works?

Real Chunks- thank you for your sympathy, hopefully it can't get much worse from here

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#51036

Conductive contamination and the elusive solution | 13 July, 2007

Oh, sure, on fine-pitch parts you need a microscope or at least a good magnifier. But, OK, you have some kind of contamination. Solder is one thing, but where are these stainless, aluminum and copper particles coming from? Stainless makes me think parts of your solder stencil or squeegee are coming off. Is this possible? You will have to identify the source of these particles before you can eliminate them. You can't get rid of this AFTER the reflow, you have to eliminate this kind of contamination before the slivers get soldered between the pads.

Jon

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#51045

Conductive contamination and the elusive solution | 16 July, 2007

Hi Scott,

Here is another thought. Check your wave solder machine visually. Does the wave flow on both sides of the nozzle? If not, you may have some dross build-up which may be causing your problem. Generally it will only happen on the very first board and this board gets the wave to flow - so all others are ok. A nagging problem that is hard to spot.

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