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DFT: Splitting Layout and Test Is A No-No

For whatever reason, some OEMs prefer to split their product projects among vendors. Such is the case when an OEM favors a particular PCB design house that does only board design and then that OEM goes to another vendor for assembly. Certainly, that OEM has specific reasons for those business moves. But you can safely say that close attention hasn’t been paid to the consequences of those actions.

Take for example, the critical testing for a PCB design. There is the highest probability of issues emerging in cases where the OEM takes design and test to separate vendors. Invariably, what occurs in this instance, is the proverbial scenario of ‘the left hand doesn’t know what the right hand is doing.’ The result can run the gamut of dire consequences, but most often it involves loss of time-to-market and money, and low product reliability.

Check out our article appearing in PCD&F/Circuits Assembly Magazine to get the full details of how best to circumvent these layout and test issues.

In the meantime, here are some tips to follow to avoid getting caught in this problematic area:

  • Best of all, deal with a one-stop shop that closely coordinates its PCB designs with its in-house layout, test, and assembly.
  • Prepare a list of question for your PCB house to determine how closely they coordinate the details of a PCB layout with test and assembly.
  • Check to see if your PCB layout engineer is so tightly scheduled with other projects that your design is getting scant attention.
  • Find out what the procedures are at your PCB house to maintain close layout and test engineering liaison.
  • Get examples from your PCB house of highly successful PCB layout and test customer projects.
  • Check out your PCB layout engineer to see how much he knows about functional test, flying probe, and ICT test guidelines and limitations. If you draw blank stares, you’d better find another PCB house.

When a layout enters its final stages, the layout designer can transfer the layout’s CAD data to the testing department where testing access reporting mechanism which tells how much test coverage is actually available on which kind of tester, keeping in mind the tester limitations. Here is where layout and test interaction pays handsome dividends. At this point, a series of mini conferences take place to discuss the steps the layout engineer needs to take to increase test coverage. This is the right layout and test scenario you want to see at your PCB house.