Frank, As Test Engineering Manager at our PCB facility, I would like to share with you our experiences of micro BGAs. These minute devices are playing havoc in test arenas all over the globe. The density of these devices are such that they physically exhaust a test systems grid area in terms of points/Sq. in. Also in order to design a test fixture that will perform well, the test pin diameter is of large concern. This alone can relate to breakout in the guide plates that will most likely cause false shorts and erratic continuity readings. We presently use an 8 plate fixture with a .016" pin. We are faced many times with the "split net" process, where the primary fixture will test 100% for isolation and a percentage of nets for continuity. The balance of the nets are then split to a secondary fixture(s) to resume the test for opens. This operation has been viable and 100% effective for us. The key is to accommodate all nets within one cycle for isolation. For continuity, which tests the integrity of a net, you could have as many fixtures as there are nets. We have had to build as many as three fixtures for a part to ensure 100% test but you need to have solid software tools to accomplish this. Also we have done "hybrid" testing, where our flying probe system picks up the remainder instead of building a secondary fixture. As far as test equipment is concerned, the progression of PCB design has far advanced what ATEs are capable of. We have 9 grid testers, one of which is on 80 mil grid, the others are 100 mil, and one flying probe unit. The focus for the present and near future has been on fixturing techniques. I have seen some of the most incredible fixturing schemes that would set your Calculus book on fire if it were near it. Many go beyond what the properties of physics allows which makes me believe there must be life on other planets. The fixtures that I've seen that work are mechanically computer aided assemblies. Bottom line is the bare board test world is in trouble and swift changes in fixture concepts are what we are developing. Your letter on the TechNet caught my attention and deserves more inquiries than I can give. Blaine R. Shelkey Test Engineering 407.752.8843 (Ph) 407.752.8868 (Fax) [log in to unmask] ################################################################ 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################