Ed has made some good points about coupons and the misconceptions about their significance. I agree that a good coupon does not necessarily mean a good PCB because there are many other important parameters which can only be checked on the PCB itself. However, I consider they are very important because we do a whole raft of tests which are not specific to the PCB design but to the process. These include daily sections checking for side to side and through hole distribution from our direct plate and pattern plate processes, and these sections include test pieces which have been soldered and thermal shocked. There are solderability tests before and after accelerated ageing, and a severe test of thermal shock for 5 or 10 cycles to test integrity of inner layer connections looking at change in resistance through a series of interconnects. There are also controlled impedance traces to test consistency across the batch, and a contamination test coupon which has to be put in a humidity chamber with constant voltage applied looking for breakdown in resistance over 21 days. These tests could not be carried out on samples from the variety of PCB's being processed day to day because they require a standard design for function and comparison. Plating thickness must be checked on the PCB's because coupons on the edge of the panel will have higher readings than coupons at the centre of the panel and the important consideration is the max and min values which have to be measured with a gauge non-destructively. X-Ray inspection of registration, AOI of circuit patterns, final Electrical Test, and hole size and dimensional checks are all carried out on the PCB itself to determine quality, not on coupons. I like to define the Quality Assurance laboratory as checking the process quality with coupons sampled from each days production, and production inspection operations checking the PCB quality of each and every batch. This division of responsibility is important to keep clear. On the original question about placement of coupons, I see no reason for the scrap biscuit panel border not to be used for positioning coupons which could then be used by the customer for pre-production tests. However, I would question the economics of having so much scrap in a biscuit panel and try to persuade them to reduce their borders as much as possible. I have seen some incredibly wasteful biscuit panels because the customer wanted to have a standard panel regardless of the shape and size of the individual pcb. Basically, the cost per panel square inch is pretty much the same for a process whether it has a pcb on it or is scrap material so keep it tight as possible. Big bare laminate borders are also bad news for plating distribution over the panel. Cheers Paul Gould Teknacron Circuits Ltd ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################