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Originally Posted by royewest /img/forum/go_quote.gif
<snip>A few pins refuse to solder to their pads. I have cleaned off the board, soaked it in too much flux, then tried resoldering. The main issue is that the solder just does not seem to want to stick to the pads.
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Two things cause this, but it can be a combination of both:
1. Not enough heat in the right place.
2. Not enough flux.
After soldering together several of these things using a small chisel point with a Hakko 936, I've come to the conclusion that ~375 deg.C. works a lot better than something lower. Everybody has their methods, but it seems to work best for me if I do a lot of the horizontal soldering in a sweeping rolling motion away from the pins - wiping, as it were. This is detailed in Tangent's vids as a "clean-up" procedure for the final touch in soldering chips like these. Seems to work for me, too.
Lower temperatures will simply not work with pads that are connected to the ground plane on the Alien DAC. Waiting for the pads to heat up in that instance causes more heat transfer to the chip. Whereas the high heat option allows a very short exposure - almost allowing the heat to dissipate before it reaches the chip because you are quickly removing the iron.
More flux will help, rather than less - as long as there's not too much solder. The flux will not allow the solder to stick to anything that's not solderable. If you have pins soldered together, then that's too much solder - not too much flux. As I said, everyone has their method - braid didn't work for me. However, a clean, hot horizontal iron works very good to wipe away excess solder on the pins.
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<snip>
* Trying a different solder. I've been working with Cardas Quad. |
That should be good enough - if it's thin. Maybe ~0.025"?
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| * Really scrubbing the board with solvent again. I've been using Electrosolve contact cleaner (what my local shop stocks) and a tooth brush. I might soak in pure alcohol, etc. |
Agree with FallenAngel in this regard. 90% Walmart alcohol and a toothbrush are fine. It helps if you do all this before adding the electrolytics and the USB connector.
You can check for continuity of the pins on the PCM chip with a meter. Check for some sort of resistance between adjacent pins. You'll get different ohm readings between adjacent pins, but as long as it's not zero, then it's OK. Then place one probe on a pin, then the other probe on the pad's destination across the board. If zero, it's a good connection. Note that there are a couple that are shorted together by the board, anyway.
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| * I will try a much more precise application of rosin flux -- using a toothpick this time, instead of an earswab that tends to flood the whole area with flux. |
I use the flux pens. I don't use them for anything else, but for the Alien, they're great. The stuff is so sticky you can almost use it to glue the chips in place prior to soldering. Again, precise application of the solder is required, not the flux. The flux can't make the solder stick to an unsolderable surface.
