And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go as ITM Consulting. We are here to address your problems, questions and situations with regard to the surface mount and through-hole assembly processes.
We have a surface mount process today, Jim. This is from C.C. C.C. inquires, what are the risks using flux only versus solder paste for placing BGAs in a hybrid lead-free environment? Interesting question. I guess the first thing that I would ask is why would you only use flux, why not solder paste? Is this a rework situation? Are we economizing here? Maybe, the cost of solder paste is certainly going up. I am wondering what the motivation is.
I agree. I am concerned about this word hybrid. In a hybrid, lead-free environment. I don’t know what that means, so I will ignore it. I agree with you. It is very common in rework to use flux only. We have talked about repairing BGAs and many practitioners have written in the comment section, which all of you out there should be checking if you are interested in one of our questions.
Our listeners and readers are often sending in some very good advice. A lot of people who are actively doing a lot of BGA rework said no we use flux only, it is much better. It would be rather problematic to use flux only in a straight reflow because you have to get a stencil without holes, apertures for the BGA and then you have to add a flux dispensing station to your pick and place system. Typically, I have only seen that used for flip chip. The risk in any case is that you will have insufficient solder and that will tend to aggravate head and pillow or non-wet opens.
As Jim said, if it is a matter of something with a very tight pitch and you are worried about bridging, that might be it. There is also other ways to approach that. I don’t know, flux only. I know with BGAs and area arrays I always have more of a phobia of getting insufficient volume. To me, flux only unless it is a really good reason, which is not stated the motivation here I would be afraid.
I have just been hearing so much about head and pillow and non-wet open due to the warping of BGA packages and the warping of the substrate that the tendency is to put extra paste there, a higher step up stencil to put higher heights of paste at the corners of your BGAs. Larger apertures to get more paste at the corners and so forth. The idea of not having any paste and going to flux seems to be counterproductive to try to minimize those defects.
I assume we will get a bunch of readers writing in about this. Based on the information C.C. sent us, we hope this helps steer C.C. in the right direction. The only thing that I will add to that is regardless of whether you are using flux only or solder paste or anything else, whatever you do please don’t solder like my brother.
And don’t solder like my brother.