How to effectively solder a pad that is part of a pour - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: June 18, 2020, 02:13:15 pm
content: I was repairing a product that had a switching voltage regulator go bad. Removing the old one was not too hard, and cleaning off the pads with solderwick also not too bad. What was incredibly difficult was getting the new part put into place. It was a SC189CSKTRT (5 pin sot 23-5) and pin 2 was the problem. The other pins soldered as expected. I would try to heat the joint at pin 2 and all it would do is smush the solder into a blob that began to interfere with pins 1/3. I'm using a Pace ADS200 and I usually solder at 700 F - should I have tried to turn the temp up some? What else?

author: ocset
author_rank: Super Contributor
timestamp: June 18, 2020, 03:06:48 pm
content: You could go up around 400degc with the solder iron temp and try...but it sounds liek you need "pre-heat"...can you put pcb on a hotplate?...if not, then what about one of those underboard hot air blowers.....or get someone else to hold a hot air gun aimed at the part while you solder. (and preheat the whole board around the sot23-5 footprint.)Use leaded solder.Use flux.If the copper pour is not essential for heatsinking, then use a metal handled scalpel to cheat and pick away some of the copper foil.(must be metal handled or you can do esd damage)

author: Shock
author_rank: Super Contributor
timestamp: June 18, 2020, 03:17:28 pm
content: Pre tin and then wick and clean both pin and pad, tack the part into place and focus on soldering the problem pin first. Apply external flux directly to the pad and pin. Clean the soldering tip and slightly tin it at the contact point. Heat up pad with the tip for several seconds. Then feed a little solder into the tip/pad/pin junction and it should wet and at least make a solder bridge (between the tip and the pin/pad).If it doesn't try using a larger tip or preheating. But if you feed and melt solder and it doesn't even wet onto the iron tip you have a dirty tip or flux issue. Try using a higher temp but everything needs to be clean, and often it's better to use a larger tip. You can even use a huge ass tip as if the tip is clean and only a minimal amount of solder has been applied to it, then it's very difficult to create accidental bridges by reflow soldering using external flux.Aside from preheating you want to avoid heating unnecessary pins at once or soldering the hardest pin last as it may cause other pins and components to act like an additional heatsinks around an already difficult joint.

author: alank2
author_rank: Super Contributor
timestamp: June 18, 2020, 06:03:09 pm
content: Thanks guys; I've got some things to try for next time!

author: Siwastaja
author_rank: Super Contributor
timestamp: June 18, 2020, 06:25:23 pm
content: Preheat the entire board! Any way you can imagine works, even just 100 degC is a huge improvement over no preheat.Think about the temperature difference to reach the melting point. If you get your board to 100-150 degC range, you are not risking the components yet, even in prolonged pre-heating, but are close to the melting point already.