The SCAR Design Engineers Must Have

Everyone makes mistakes. When we do, we all swallow our pride, get past the embarrassment, learn, and move on. But what happens if the same mistake is made over and over again or goes unrecognized? We move into a cycle of perpetual failure, with the associated corrective action and lost opportunity costs. That's why you need best-practices for handling process, procedure, and people failures.

About a year ago, I bought several thousand dollars worth of bare printed circuit boards (PCBs). I requested the fab house to forward them to an assembler as part of a consignment kit for an assembly that added about $250 in component costs to each stuffed board's value. When I received the completed assemblies back for testing prior to system level assembly, not one of the boards was fully functional.

There did not seem to be a pattern in the failure modes from board to board. Upon closer inspection with the aid of a stereo microscope, it was discovered that the copper trace widths seemed unusually thin in some places, and downright raggedy-edged in others. We were looking at boards that had been seriously over-etched. The proper calls were made. The proper apologies were given and received, and discussions about the proper reparations ensued. I should state that we had been using the same fab house for years without experiencing any difficulties.

Part of our standard operating procedure was to have the boards electrically tested and visually inspected prior to shipment from the PCB fab house. Also, as part of the procedure, we would test one solder sample that we could "ohm out" to make sure that power was not shorted to ground prior to stuffing any components. What went wrong? I needed to know, and, more importantly, I had to guarantee this would never happen again. Enter the Supplier Corrective Action Request (SCAR) and internal Corrective Action Request (CAR) procedures and forms.

The SCAR is one procedure that is aptly named. When you receive a wound and it heals, sometimes there is an ugly scar that reminds you that you should not play Superman and jump off your roof with just a bath towel cape wrapped around your neck for extra lift -- speaking from experience here. In the same manner, having a SCAR report form on file that details your supplier's mistakes will remind both you and the supplier that errant actions won't "fly" with your company. For too many companies, here is how things work without a SCAR procedure:

1. The problem happens
2. The problem is recognized by the victim of the problem
3. The source of the problem is investigated
4. The party responsible takes full ownership of the problem or loses his or her job and all respect
5. The responsible party promises it will never happen again
6. he problem happens again
7. Return to step 2 and repeat steps 1 to 6 until the company initiates a formal SCAR/CAR procedure.

The value of the SCAR or CAR is that it is not only used to pinpoint the true nature of the problem, but it requires the person behind the problem to state the actions taken to guarantee the problem will never happen again, and to identify the cause of the problem using Root Cause Analysis (RCA) techniques. The remedies may include the supplier modifying materials, documents, procedures, processes, and employee training and certification programs.

As it turned out, after initiating the SCAR procedure, the fab house reported that the over-etching occurred because our boards were panelized with another company's boards to save FR4 material waste. But the etching process for our boards was different than the company's boards on the same panel. The operator put all the boards through the same etch process, and we got the thin end of the deal. On the SCAR returned to us with this explanation was also a corrective action statement that included an extra inspection step for the etching work station.

That procedure required a signature verifying that the etch instructions had been read for each unique board prior to beginning the etch process. We modified the instruction to include a copy of the etch station signature being sent to us on every board fabrication. Why didn’t the electrical test catch the problem? Because the boards were batched together and only the company's boards were tested.

Also, in our own CAR was a statement that required an internal procedural change: Prior to any shipment from the fab house to the assembler, the solder sample board would need to be sent to us for electrical testing and visual inspection. We also stated that our boards were never to be put on panels with any other company's boards. We never had another problem.

In summary, be sure to verify the solution is in place and that it's effective. If necessary, visit the supplier and see how readily available the modified process or procedure is to the individual or team responsible for the operation. The modified procedures should be part of the training certifications on file.

Because we were trying to save time and additional freight costs by having the fab house send the bare boards directly to the assembly facility, we paid a heavy price. But because we instituted the SCAR/CAR procedures and changed how things were done, we probably saved even more money than we had lost through cost avoidance savings on future builds.

The SCAR form and instructions on completing it are available here. You can also share this information on SCAR and CAR procedures with key players in your company.