Harvey,
? All good info. I have watched videos that show some things I always wondered how they did that without a machine doing it for them. Very interesting. I recently watched a guy using a tip that had a pocket in it to hold extra solder (maybe a hoof tip). He was soldering a bunch of DIPS as he tested different solders. Flux played a key role in this demo. The smallest diameter solder I have now is 0.020 but if I need it, I will get some 0.015.
Thanks,
Dave
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On 11/5/2019 6:58 PM, Harvey White wrote:
Somewhat easier method, but it diverges after you tack down the opposite pins.? If you don't do that, then the solder hardening pulls the chip out of alignment, so do diagonals first then go for the rest.
Once you have all the pins aligned properly with the corners soldered, then add more flux.? You want flux on the top of the pins to the chip.
I use about a 50 mil/ 1/16 diameter metcal tip.
I've found that putting a little solder on the tip (a solder reservoir, but not a hoof tip) and running the tip from the end of the pad up to the pin allows solder to flow from the tip down onto the pad, and covers the "foot" of the chip pin.? If you should happen to hit two pins at the same time, solder may flow to both without shorting the pins.
If you do short the pins, then adding flux and reheating both *can* separate them (not always).? Otherwise the solder wick works wonders.
Note that this works best on boards with a solder mask.
I use 0.015 solder, eutectic, with a flux core.
Harvey
On 11/5/2019 5:59 PM, Jim Higgins wrote:
Lead-free solder is mostly tin, with trace metallic additives to reduce the likelihood that the solder will grow "whiskers."
If interested in details on "tin whiskers," the following is a good overview. You can't retouch a joint to remove whiskers in a satellite.
(metallurgy)
I only mention the following because I can't see much use for soldering paste except for close spaced leads or if you use a reflow oven.
I've done very little soldering of IC packages with many closely spaced leads on four sides. Used to do MIL Spec soldering in the late 60s, but we had nothing like that back then. I used tin-lead solder then and now... darn near hair thin when soldering closely spaced IC packages. Get the super thin stuff and if too thin just double or triple it... thin so there's no chance of getting too much solder and having it short something somewhere out of sight... like under the IC.
My approach - on the rare occasions these days - is to place the multi pin package and tack the thing down with pins aligned with the pads via a few leads on each corner. Then with plenty of flux, solder all leads on one side without worrying whether they're shorted - just don't apply so much solder that it flows where it can't be seen. The less the better, but be sure all pins are soldered to the pads even if shorted. Repeat for all sides. Now apply more flux and lay solder wick along one side and run the soldering tip along it to suck up all excess solder. Same for the other three sides. Inspect closely and apply solder and/or wick if needed... always with plenty of flux.
With this approach the leads all must be at the same level so when the chip is resting on the board before soldering, all leads are in contact with the pads... or at least so close that solder wick won't pull out the solder between lead and pad. Works like a charm. How fast you move the soldering iron tip along the solder wick plays a role in the quality of the job and the need for rework. Start off faster and go slower if pins remain shorted.
Jim H
