by 5B4AIY » 14 Jun 2017 14:00
Hi, Alain,
I used RMA (Rosin Mildly Activated) flux that I obtained on eBay. It has the brand name of Powerfix, and is to DIN EN 29454-1, and is manufactured by Abraham Diederichs GmbH & Co, Oberkamper Strasse 37-39, D-42349, Wuppertal, Germany. This flux is a soft, light honey coloured paste, and is easily removed with de-natured alcohol. After finishing all the soldering, I generally clean the board first with a soft cloth soaked in alcohol, finally removing any remaining traces with a Q-tip moistened with alcohol.
As for the temperature, I tend to use a fairly high setting, typically around 320C - 330C. I have found that this very quickly melts the flux and solder and makes a perfect joint within 1 to 2 seconds, thus minimising the thermal exposure. At lower temperatures it takes somewhat longer to melt the solder, and the pads and components are then subjected to a greater thermal input than with a short time with the soldering iron tip at a higher temperature.
For soldering the leads of the ICs, with the chip in position I apply the tip of the soldering iron to the lead along with the solder, and then 'stroke' the iron along the lead to the board, and this results in a perfect joint. For the other ICs, I find that they are sufficiently large that I can hold them in place with the tip of my finger and then tack solder one of the leads to hold it in place. Then I carefully examine it to ensure that it is the correct device, correctly oriented and aligned. The next step is to tack solder the opposite corner lead in place, and make one final check. With only the two corner leads 'tacked' onto the pads, it is an easy matter to remove and re-position the device if it is not perfectly oriented or aligned. If everything is OK, then I can place the solder on each lead in turn and touch it with the tip of the soldering iron, remove the solder, then the tip of the iron, and, that's it!
The solder I used was obtained from the same supplier as the Juma kit. They marketed at that time a solder pack containing not only suitable solder, but also tweezers and a small bottle of liquid flux, which I did not use, preferring the paste. The solder was normal 60/40 rosin-cored tin-lead solder, not the non-lead solder that is now being used as this requires even higher temperatures to melt.
Perhaps I should add, that if you do not like the idea of using a spot of epoxy to hold the DDS/PIC chips in position, then a small blob of something like Blu-Tak, or Faber-Castell 'Tack-It' creative removable adhesive that you can get in stationery stores, craft shops, etc, also works. The beauty of this method is that the chip is not permanently attached to the PCB, and thus if you should ever have to remove it, then after clipping all the leads, it will simply lift off, whereas with epoxy it is more difficult, and you may also remove any tracks that were under the epoxy as well.
73, Adrian, 5B4AIY