ATE tests: VIA form factor and NES to test

Hi folks,

I'm routing a board which will be tested by an ATE system (Bottom Access). The questions are:

1) VIA FORM FACTOR Let's suppose I have a net on the TOP layer and I need to test it: I have to add a VIA. Are there any rules about the form factor of the VIA? I'm talking about the hole diameter, the pad diameter on TOP, the pad diameter on BOTTOM

2) NETS TO TEST Let's suppose I have a 19-wire bus that connect the CPU to some external RAM memory. No passive components in the middle. Do I need to add a test point on these wire?

3) DESIGN FOR TESTABILITY DOCS Are there any standard documents explaining how to route an ATE-ready board?

thanks for any help, Enrico

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There are no hard and fast answers to these questions. You need to talk to the production people who will build and test the board, the tooling people who will make the test fixture and you need to read the manuals (and possibly get training) for the ATE equipment.

There are many tricks to avoid adding test pads to every net - that is what JTAG was invented for.

Michael Kellett

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The JTAG port is a great tool but just a few IC's have it.


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You can use jtag to help, but will probably need pogo pins anyway. They can make any size pogo pins, but popular ones are 2.54mm, 2mm and

1.25mm. 2.54mm is more reliable and cheaper to make, but 1.25mm save PCB spaces.
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JTAG can be used to stimulate the board just like the CPU could. It allows you to test a board without loading the Flash or if the board uses PROM. Otherwise, a lot of testing can be done in software with a separate firmware load in Flash which is overwritten when the board passes test. JTAG is supported by software which will accept a net list and description of the various memory and other devices on the board to automatically generate test vectors. JTAG can also be used to program Flash memory.

It's not a bad way to go, but if you are doing really high volumes, board probe ATE is faster. On the other hand, most boards are so cheap these days, that rather than fix them, they get tossed...


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