Clever Wedges That Will Increase Your PCB Assembly Yield

If there’s one thing that will bring down the yield of your PCB assembly, it’s your solder paste. Put too much on, and you’ll get bridged leads. If you don’t put enough on, that pad might not make good contact. [ScalarElectric] has an amazing trick that’s sure to astonish and astound. Just use wedges and you’ll get better yield with fine-pitched components.

The trick here is to define the cream/solder paste layer of each package as a wedge on each pad instead of the usual rectangle. This gives a few benefits, the largest being the increased gap between paste shapes. You’re also getting a reduction in the total amount of paste applied, and a subsequent improvement in yield. (Reportedly, we’d love to see some data on this.)

PCB design tools usually have a way to alter the size of the cream/solder paste layer of a design, and indeed one option is to simply shrink the size of the paste layer elements. The trick to the wedges is increasing the total distance between solderpaste blobs while keeping the total amount of solderpaste high. This technique can be used down to 0.5mm pitch parts, and everything works like a charm.

While this is a little outside of our wheelhouse here at Hackaday — it is, after all, a novel use of existing tools that is mostly applicable to electronic design and production. [Ed Note: Sarcasm.] You can check out a few pics of this technique in the slideshow below. If you test this technique out, be sure to let us know how it went!

This slideshow requires JavaScript.

Solder Paste Fridge

MightyOhm’s laboratories have recently decided to start tackling more surface mount work. As part of this upgrade to SMD hot air reflow stations, they’re handling a lot of solder paste. Solder paste is happy at less than 50degF and above freezing, and [Jeff] didn’t want to chance that lead infiltrating his Manwich, so he built this solder paste fridge. The main unit is a standard 12V peltier based travel cooler. He attached a surplus PID controller with a K-type thermocouple to maintain the temperature while preventing the cooler from being always on. The only adjustment he really had to make was adding a bleed resistor to force the MOSFET to turn off. You can find more pictures of his project on Flickr.

Solder Paste And Reflow How-to

I was poking around spark fun electronics, and came across this interesting walk through showing spark fun’s solder stenciling technique. (I’d put on some gloves before handling that much lead paste) They top it off with some alternative ways of doing reflow work. My favorite has to be the target hotplate method. It’s a nice introduction if you’re interested in doing SMD work to save money and space on your projects [but not sanity. say goodbye to that] Me? I’ve used a 15 watt weller with a dremel modified small tip. It works great if you’ve got some one of those syringes of heat activated glue. Place, bake and solder.