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Tips for thinking outside the board

Posted: 28 Oct 2013     Print Version  Bookmark and Share

Keywords:PCB  manufacturer  prototype  panel  resistor 

When I started with an earlier iteration of my current employer, about 23 years ago, we used an independent PCB designer who was renting some space at a PCB manufacturer. ISO9000, safety, and environmental rules were laxer then—he was given the run of the place, so he got to know the process pretty well.

When you submit a PCB to a board shop, they will typically "panelise" it—that is, they create multiple copies of the same board on a larger board (panel). Now, for some reason our designer started creating his own panels—either he thought he was helping the board shop out, or he preferred doing things his own way, or he had some other reason that remains unknown. The thing is that we were growing as an organisation, so the PCB designer decided to accept a job with us because it offered more security than he had on his own, and he brought all his methods and practices along with him.

We had developed a relationship with the aforesaid PCB manufacturer. We had an understanding that a prototype run of a panel (10.5" x 16.5") would cost about $300 with a two-week turn-around and we would get at least three panels of however many PCBs there were on each panel. Of course, it could be that we obtained this arrangement because we were a large customer when it came to production boards. Some of the products we made consisted of two different boards, in which case a panel would be made with multiples of two different boards on the same panel.

Over time, the number of engineers feeding the PCB designer increased to six, with each working on one or more prototypes. At some point, the penny dropped, and we realised we could put any number of different boards within the prototype panel and it would still cost the $300. That meant that we could amortise the prototype development costs, provided we could live with the delay whilst designs were added to the panel.

Other considerations were that they had to have the same board and plating thickness. (The price for a panel has increased to about $700 over time, and our production volumes in Canada have dropped, but we continue to use the same approach with different PCB manufacturers.)

Figure 1: A mixed prototype panel with four totally different PCBs.

Hint No. 1: Accumulate multiple prototype PCB designs onto a single panel to amortise your prototype costs. Of course, when we move to production, we have only one type of board on a panel (or pairs of boards if the product was designed that way).

One of the PCBs we produce is tiny—only 5mm x 20mm—and is very difficult to hold when testing. It is little more than an LED and resistor, so the test simply requires powering-up the circuit and performing a visual check. Someone cleverly decided that if we brought out traces across the breakouts for each PCB in the panel, we could common both terminals and bring them to a suitable point on the panel, outside of the actual product PCBs as illustrated in figure 2.

Figure 2: Panel with many small boards. Don't let the scale fool you—each board is 5mm x 20mm. It is not clear, but the white surround indicates each board's cutout. The breakouts aren't very clear here. Observe the two test points on the right.

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