This is just one article in a series of articles discussing tips and tricks for using a selective soldering machine. Here at Worthington Assembly Inc. we have a selective soldering machine manufactured by RPS Automation. Our particular model is a 2010 Rhythm model. These article are written by the same person who's used this machine every day for over a year. Heat helps. Anytime you're soldering anything, the more heat the better. Even when soldering board by hand with a soldering iron, having the board a little warm before you start can help a lot, especially for boards with large ground planes.
One of the boards we run quite often here has just a couple of small connectors. It's a lead-free board but it was a real challenge to get it to solder consistently without bridging. We couldn't figure out what the issue was but after some experimentation, we discovered that heating the specific area we were about to solder helps for just a few seconds made all the difference.
As you can see in the image below, there is a small dot of orange in the middle of where we drag solder across the connector.
When we program the machine, we edit that specific point to dwell for about 3 seconds. We also add a negative z offset of about 5mm. What will happen is the machine will drive to that specific location, raise the nozzle as if about to solder there, but then never come into contact with the board. Heat will just pour out of the nozzle and the nitrogen shroud and get what whole area nice and warm. Right after that we just go ahead and drag solder across the connector and it comes out beautiful every single time. Since we've implemented this one change to this assembly, we have never had a single bridge. Ever.
Preheating is always helpful. We recommend using a hot air preheater before you even put the board inside the machine. But these are rather pricey. So why not just use your machine instead? (unless of course you need your machine to run as absolutely fast as possible)
As always, if you have any questions, feel free to give me a call or send me an email.