Design for Test (DFT)

The Cheapest Time to Fix Testability Is Before the Board Exists

Design for Manufacture is often the primary consideration; Design for Test is often overlooked. The two pull in similar directions but not identical ones, and when only the first gets a seat at the table the second is left to be dealt with afterwards — by which point the choices have already been made.

By involving us early in your design process, we can work with you to determine not only the best way to test your PCBs, but also how to ensure their testability is maximised.

Most of what decides testability is set at layout, and costs nothing to get right at that stage:

• Test point provision, placement and access
• Probe-side clearance and keep-outs
• Nets buried under BGAs and other unreachable connections
• JTAG chain arrangement and accessibility for boundary scan
• Programming and debug access
• Power and control needed to run the board at test

Once the layout is frozen, none of that is free any more. A net with no access stays untestable for the life of the product, and the coverage you cannot get structurally has to be bought back somewhere else — usually with a more complex functional test, or by finding the fault later than you would like.

Because we run test daily as well as supplying the equipment, the advice is grounded in what actually probes and what does not, rather than in what should work in principle.

Call us to discuss your needs and leverage our understanding of test.