Board Stress Analysis, Should you pay for this? As with any product, service or feature, you need to ask "What do I gain when paying for this?"
Recently, some fixture vendors have started charging for Board Stress Analysis (BSA). Blame it on RoHS, probe density, no-clean, or a variety of other test issues but you need to know that the board is not going to flex, too much, during test. Board Stress Analysis will ESTIMATE how much force you have on your board during test. Good information to know. If the Analysis estimates too much force in a given area, the fixture design needs to be modified with additional supports, push fingers, lower force probes, or relocating probes. But again, should you pay for this.
QxQ has been providing Board Stress Analysis since we started building fixtures in 1992. Evaluating the locations and quantities of push fingers and support is critical to the operation of the fixture You see, for years fixture vendors would provide this evaluation as a SERVICE to their customers. Now, some vendors figure they can get more of your money by charging for this service. Shouldn't your fixture vendor provide this? At QxQ we think so.
Remember, Board Stress Analysis is an ESTIMATE of stress. QxQ uses precise formulas to determine this estimate. If you want a pretty, 3-D graphic showing this information as a picture, unfortunately we will need to charge for that as well. Software tools are expensive. Do you get better information with the graphic? Well, the graphic is based off of, that's right, formulas. Therefore, the graphic (as with our formulas) identifies potential problem areas showing where the fixture design needs to be modified with additional supports, push fingers, lower force probes, or relocating probes.
Actual Report vs. Estimate report. The truest evaluation on Board Stress is after the fixture is built. Using the actual operation of the fixture. BSA is an estimate; however Strain Gauge Testing is ACTUAL. QxQ has been providing Strain Gauge Testing for several years. This process adds up to a day to the turn time, and the cost depends on the number of BGA's being tested. We can also place sensors on various points on the board, however BGA's are susceptible to the most damage from board stress, therefore we locate the sensors around the BGA's.
Strain Gauge reports will be provided, assuring minimal stress on the board. This test is valuable to assure the actual strain on the board during test. QxQ also keeps this information archived, and can retest the fixture at any time. This can be very valuable if the fixture has been modified or refurbished. Strain Gauge Testing does require a loaded board dedicated to this test.
In summary, Strain Gauge Testing is actual and assures the fixture operation is within tolerances. Board Stress analysis is an estimate, however Board Stress Analysis is important. And yes, your fixture vendor should provide an analysis on every fixture. Should you pay for it? It depends how much you want to pay for a picture.
DFT Guidelines. Contact QxQ for Design for Test standards.
When to use Guided Probe, Zero Flex chart. To determine when the fixture should have Zero Flex, Guided Probe or Both, simply look at the easy reference chart developed by QxQ. Request yours today.