Is it possible to use JTAG at debug & repair depots to reduce the cost of diagnosing bad boards?
The overall cost of manufacturing products bears a financial burden given that some number of boards that roll off the production line do not function due to an assembly defect. It is up to the Contract Manufacturer (CM) to quickly isolate the root cause of the failure (if possible), then rework or repair the board to make it ready to ship. Further, the CMs often take in faulty returned material from the OEM’s customers that failed sometime during the lifetime of the product. The same debug methodologies that are used for production material debug & repair are used for return material authorization (RMA) types of defects.
The financial implications of the cost of repair, and who bears it, are often difficult to determine. Contracts between OEMs and CMs often stipulate that the CM provide a quantity of “good boards” at a fixed cost per board. It would seem that in this model, the CM bears the expense for any process inefficiencies that decrease yield or increase the mean time to repair. But, one could argue that this cost is passed back to the OEM, based on a higher price per unit quantity produced. Realistically, it is a shared burden between the OEM and the CM: the allocated cost per board of time wasted in the debug process costs everyone money, and eventually this cost flows down to the consumer.
So, given this situation, is it worth considering making process improvements to reduce the time taken for debug & repair? This is a question we asked a customer recently, who shared some very interesting results. In this instance, their repair depot was processing approximately 600 boards of a certain type per week that were found to have assembly defects. It was taking an average of 72 minutes to successfully diagnose the failure root cause and go to the rework stage. Once they introduced JTAG (boundary-scan) debug & repair test software into their flow, the average time for diagnosis shrank to 11 minutes. What is that 60-minute time saving worth?
The financial equation is highly influenced by the fact that many products are manufactured in Asia, where the cost of time may be very low, compared to North American or European counterparts. In China, the burdened cost of a factory operator is about $1,000 USD per month, or about $6/hour. So, given a time savings of 60 minutes, the savings is $6/board.
Simple math tells us that this facility can save about (600 boards/week X $6 X 50 weeks/year) = $180,000 USD annually.
The overall benefit has to be netted against the cost of implementation and boundary-scan test tool cost. But, the ScanWorks JTAG tool is fairly inexpensive, and ease-of-use for boundary scan implementation is fairly high.
The financial equation is variable depending upon the volume of the defective boards, labor cost, time taken for debug, and so on. But, it’s certainly worth a discussion based upon the “time = money” paradigm.
An interesting Case Study on JTAG cost savings in repair is with Reptron Manufacturing Services (now Kimball Electronics): Case Study: Boundary-Scan Test for Reptron Manufacturing.