Nuts and Volts - September 2011

By John D. Collier

BUILD A CIRCUIT BOARD

ASSEMBLY JIG

I spend a considerable amount of time assembling and soldering circuit boards for my profession, as well as a hobby. One of my biggest frustrations has always been securing the PCB in such a way that it cannot move or vibrate, but still allows plenty of access for the soldering iron. Over the years, I have purchased — and been disappointed with — various types of circuit board vises and fixtures. The ubiquitous “third hand” gripper was too flimsy. Others had jaws specifically for circuit boards, but I found them to be too deep or improperly sized. Most could not hold more than one PCB at a time. And there was one feature in particular that I was looking for: a reliable way to hold through-hole components in place, upside down, while I soldered on the other side of the board. This article describes my solution.

■ FIGURE 1. The completed assembly jig, with side supports in use.

THE DESIGN

I loosely based my design on photos I had seen of professional circuit board reworking equipment (costing in the hundreds or even thousands of dollars). These systems use a piece of soft foam rubber to hold components in place, allowing soldering work to be done on the opposite side. I decided to use T-slotted extruded aluminum for the jig frame, from 80/20, Inc. ( www.8020.net). The T-slot system is very versatile, as T-nuts can be used to mount

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components at any location on any of the four sides.

Two notched rails were fabricated which capture the circuit board(s) and can be adjusted as necessary in the T-slots. The foam is attached to a backer plate which is inserted through the opposite side of the jig and applies slight pressure to the circuit board. Knowing that this foam would be installed and removed frequently, I chose to use quick-release toggle clamps to hold it in place.

After trying out the jig with several different PCBs, I found that certain large or odd-sized components had to be manually held in place while being soldered.

This proved difficult since the parts are normally underneath the jig during soldering. My solution was to install two strips to the front of the jig using T-nuts which are normally parallel to the extrusion, but can be rotated 90 degrees to provide an extra set of feet. The jig can then be set on its side, allowing access to both sides of the circuit board. Figure 1 shows the jig in this setup.