Thierauf Design & Consulting: Signal Integrity Design, Analysis & Training

Several years ago I was doing a “walk through” of a client’s layout database. This is where I use a CAD viewer to look at the database (either the Gerber files or, if a custom tool is used, the layer files created by that tool). My client had electronically checked and simulated the database with one of the SI tools on the market, and the tool had declared the layout clean. Good to go. Ready for fab.


My client’s engineering department was annoyed (skeptical, in fact) that I wanted to visually inspect each layer in the database because they were under some serious time pressure. The pricy SI tool which management agreed to buy (and their engineers used on the database) had declared the board ready, and because the project was late, just about everyone wanted the board in the lab now, if not sooner. Except maybe the diagnostic engineer who was behind schedule in developing test patterns for DVT, and who was, I think, secretly hoping we’d find a killer problem to hold up fab for a couple of weeks. But, because of my history with some of the folks at the firm, management reluctantly gave me one day to wonder through the database.

It didn’t take that long. Within about 2 hours a half a dozen abnormalities needing to be corrected had poped out. The diag engineer was thrilled (management was not).

I’ll post more on this in the future, but the take home message is that SI tools are wonderful, and necessary. In fact, in many instances SI tools are absolutely vital to getting a product out the door on time with minimum hardware debug. Just don’t let the tools get in the way of using your brain. As an SI engineer, or design engineer doing SI work, you understand context and can see the big picture far better than any tool.

Don’t let the report generated by a nice looking GUI fool you into thinking that the tool is expert. It probably isn’t. And, be absolutely sure to include enough time in your layout/fab schedule to do a walk through.