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DEBUNKING ENGINEERING MYTHS

by Robert Kondner

Start ý Obsolete Parts ý Code Reuse and Object Environments ý Sources and PDF

OBSOLETE PARTS

If I had a nickel for every vendor that told me I was using an obsolete part, I might not be able to retire, but I could buy a nice lunch. The salespeople alone are not to blameýmanufacturers pushing new products are feeding the frenzy. From a feature standpoint, a manufacturerýs new part might make the previous part obsolete for a new design, but it does not imply that the older part should not be used in a new design.

REDUCING PART COUNT REDUCES COST

I always get a chuckle when someone selling a new wiz-bang component takes the total assembly cost and divides by the component count to show the value of reducing part count. I chuckle because some contract board assembly is based on component cost, not component count. Using a more expensive component will increase assembly cost. A good assembly shop will consider component counts, but as a portion of the quoted cost, the savings on one or two components is simply not important.

Even major savings in PCB space can be difficult to justify. If changing a component can reduce PCB layer count, then go for it. However, using a couple of 50-mil SOICs in place of a single, large 20-mil QFP will bring a smile to your assembly folks. Whether or not that smile means a lower assembly cost is another question. Unless a board is tight, 50-mil SOICs are easier to route, place, solder, and test.

OVER THE WALL VS. CONCURRENT DESIGN

We hear a lot about concurrent engineering. I believe that the best environment in which to develop a product is one with good communications. In the real world, however, not all individuals have the skills to be involved in all areas of expertise. Any good schedule has points called milestones, which usually include a set of deliverables to the next phase. Good milestone examples include a netlist or mechanical drawing. One advantage of over-the-wall structures is, if you pass something incomplete, it bounces back into your lap.

It has been my privilege to pass projects to qualified PCB-layout and mechanical people. It has always been my experience that giving them both information and independence results in incredible productivity. If you want to win the Super Bowl, you need good players who know how and when to pass the ball.

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