“What does “Stamp Out Rework” mean?”
In the circuit assembly business, production yield is the measurement of quality. In other words, the higher the first pass yield, the better the quality of the lot. In addition, the higher the yield, the less rework and scrap is generated at the end of the production line. If the rework step was eliminated or “stamped out”, manufacturers would not only realize higher quality, but improved profitability.
“How does rework affect profitability?”
Ideally, your price (what you sell your end product for) is calculated as the sum of the cost of materials, equipment, and labor plus profit. But in the real world, most manufacturers make anticipated yield part of the price equation. If your current first-pass yield is lower than your original projections, a yield improvement strategy will help you to meet your target margins. If your process meets your initial yield and margin estimates, any improvement in yield will fall to the bottom line as an improvement in profits.
“How does my company begin to ‘Stamp Out Rework’?”
Look at areas for process improvement as early in the production line. Most experts agree that controlling solder paste printing is a key to high-yield production. Some even say that as much as 50% of all soldering defects can be traced back to the deposition (printing) process. That’s not surprising, since it has been reported that there are approximately 40 variables in the solder paste printing process. Controlling such a volatile process requires identifying characteristics that will predict process performance and finding a suitable tool to measure those characteristics.
“Why solder paste measurement?”
Consider the cost of rework at each stage of assembly. Washing and reprocessing a poorly printed board will take much less time and resources than repairing solder defects on a fully populated, reflowed board. A quick rule of thumb for estimating rework costs is the “10X Rule”. Simply, it states that rework costs at each stage of the assembly process will be 10 times greater than at the previous stage. For example, if a print failure costs only $.50 to correct, leaving it to be fixed after reflow will cost $5.00.
That same failure left unchecked until after the ICT/functional test (when the PCB is fully populated or mounted in an assembly) will cost $50.00 to fix. And if a poorly printed (and reflowed) solder joint fails in the field, the costs associated with resolving the problem and soothing the customer could run $500.00, or more. It’s easy to see how the savings attributed to finding defects as early as possible in the process (i.e. at the printing stage) can easily justify the costs associated with obtaining solder paste measurement equipment and implementing a paste inspection strategy.
“Is it possible to completely eliminate the rework process?”
As complex and ever-changing as the circuit assembly business is, the road to complete elimination of the rework step, indicating “Zero Defects”, is long. However, your company can begin down that path by implementing a strategy to eliminate soldering defects, catching problems as early as possible in the process, before they turn into bad solder joints.
“What should I do with the “Stamp Out Rework” sign?”
By placing this poster in your production area, you let all who see it know that your company, workgroup – and even your customers – are making a commitment to improving the quality of your products and the profitability of your organization by adopting process strategies to improve production yields.
