Schmart prototyping

Prototyping is one of those things we need to do but recently SchmartBoard has made it a little easier. Over many years I have used a variety of commercial systems as well as specialised boards I designed for myself. But nobody really has a system quite like the SchmartBoard.

A SchmartBoard is exactly 2 inches (50.8mm) square and it has a specialised pattern on it which allows you to hand solder integrated circuits with pad or pin pitches as small as 0.4mm. I haven't used the 0.4mm yet, but I can tell you that 0.5mm and 0.65mm are a soda to handle, including the 0.5mm QFN style pattern seen here.

This board is a little unusual in that it has two patterns on it, one a 32pin, which can be used for things like the CP2102/3 USB devices, or an Atmel AVR processor, while the 10 pin one can be used for a variety of power devices and driver devices from manufacturers such as Maxim. I tried all manner of techniques for hand soldering QFN's, but this is the only one that works.

So how do they do it?
The SchmartBoard actually has a shallow groove where the IC pin sits. And that is the secret! My method is a little different to that in the documentation, before I mount the device I use a solder flux pen (felt tipped), my favourite being the Kester #2331-ZX which I usually buy from DigiKey, and applying a small amount of flux along the board where the pins will sit. I carefully place the IC using tweezers (a magnifier does help!) and while holding the device down with the tweezer points I carefully tack solder two diagonally located pins on the device.

Then I carefully check alignment and solder the remaining pins, usually using an STTC-106 tip in my Metcal MX-500 solder station. Of course you don't REALLY have to have a $600 station like a Metcal. Your good old fashioned Weller or whatever will work with a VERY fine tip of appropriate temperature.

After soldering the device I clean up any excess flux with an MG Chemicals Flux Remover Pen 4140-P, again from DigiKey.