With all the buzz around automation, paperless operation, and integrated processes, it’s time to think about how the connected systems work within an electrical test department. We are all familiar with computer-aided design (CAD) and computer-aided manufacturing (CAM), but with electrical test we can also add computer-aided test (CAT) and computer-aided repair (CAR).
Back in the ‘80s, Bob Whitehead, of Electronic Packaging Company in Dallas, Texas, coined the phrase “The 4 Cs” with his vision of an integrated electrical test platform. Although Bob is no longer with us, I’m sure he would smile to see that his vision has grown even further than perhaps he imagined. As many of us can remember back in the day, ET was nothing more than a couple drilled plexiglass plates, some one-inch pins and a universal single-sided test machine capable of “self-learning,” a “known good board,” and then testing of the subsequent product. There was even the learn-comparison avenue for which you had no known good board and learned one from the lot, and then compared the rest to the learned board. It worked well for the time being unless the entire lot was bad. Bad board learned, all bad boards the same, the machine said “pass.” This would be a dangerous concept today to be sure.
So, what’s in ET today? Self-learning is a thing of the past in most cases, thank goodness. The fixture testers have evolved from the original single side, single-density versions to double density, quad density and even octal density! They can test by pre-programmed data sets, provide data logging, serialization, print bar codes, and even process the product automatically.
This is where computer-aided test (CAT) really shines. In ET today, orders can be processed simultaneously on multiple machines with floor ERP systems tracking results from any given machine. Serial number, operator, parameters, and yield can all be captured seamlessly. Between fixture testers and flying probes, the flying probes can work with the fixture testers to verify non-conforming product. This keeps the fixture testers running and not waiting to troubleshoot each board. The probers can validate if the defects are real from the fixture testers and pass the product with errors that are deemed false. This is done by the test floor integration process where data fault logs are captured, the board receives a serialized bar code, and the flying probe reads that barcode. It then reads the fault data and performs a retest based on the same CAM data used at the fixture tester. Conforming boards can automatically be marked as well.
Continuing the process, passed boards receive a passed tag while non-conforming product will receive a fault tag, complete with barcode. This fault data is also captured. We move now to CAR. The product moves to the repair/ troubleshooting area where the bar codes can be read, and the fault locations presented on a screen for easy translation to the board itself. It can be quickly determined whether the board can be reworked, or the fault requires unfavorable disposition (scrap). From here, reconciliation of the order from all facets of the ET operation can be completed. Pass/fail reconciliation, serialization, and final inspection can all be achieved.
So, we can see that the computer and automation age has hit ET as well. Many processes in ET are no longer the manual, tedious processes of the past. Still, the entire manufacturing theatre relies on the OEM to begin the process via CAD. Then the full integrated process of CAM through CAR exists under one umbrella. Even now, the once manual HiPot (dielectric breakdown) test has evolved to automated options. Flying probes are now able to automatically perform the tests that once were the tasks of a single operator.
Although an operator is still required for the machine, the tedious movements of probes to different pairs and waiting for the test is now automated. So we see in Figure 1 that, although CAD (OEM) is still the first attribute, manufacturing including the functions of ET are all in the connection equation.
Todd Kolmodin is the vice president of quality for Gardien Services USA, and an expert in electrical test and reliability issues. To read past columns, or to contact Kolmodin, click here.
This article originally appeared in the May 2018 issue of PCB007 Magazine, click here.