Issue link: https://iconnect007.uberflip.com/i/1428512
16 PCB007 MAGAZINE I NOVEMBER 2021 guys say, "We want it 5%," and the manufac- turer can't get there. For print and etch, it must be right on the money, or you won't get that impedance. For every percent change it's an order of magnitude of accuracy you have in the process. You're getting down to micro-pixel strength on your photoplotting and etching. You're probably having to get down to laser etching to get 2%. Holden: Have they solved the problems with OSP so that it doesn't foul up the probe tips? Kolmodin: OSP is one of the most difficult fin- ishes out there; the main way to get around that is to test before OSP. Otherwise—even before flying probes, even with grid testers or fixture testers—trying to probe a pad with organic coating on it is an absolute nightmare. Usu- ally, you won't get through it and you will have overflow opens and all that. e best thing is to get it from the process prior to OSP in the test, and back into organic coat before you start oxi- dizing the pads. If the organic coating is to be applied, the best way to test is aer your criti- cal process or measurements are done. I don't know a way around that one, really. Holden: When I was at HP, we were not get- ting test probes on the surface or test pads, so we came up with a bead probe, which is just expanding the trace and putting solder paste on it so your probe could have a place that wasn't covered with solder mask and didn't affect the elec- trical impedance. If you have accu- rate flying probe or bed of nails, you could probably hit these small pads in traces. Kolmodin: It was a challenge back then. But now that you mention it, when designers decide to use wire bond, direct probing is out of the question. You can't do it. Tell a prober to hit it but aer that you've basically destroyed the bonding surface no matter how light you hit it. You must come up with another way. You must short out the wire bond area, and test somewhere else to check for continuity and shorts. But they would fan out something in the design level if you got wire bond, test IOs. Wire bond is common in some of that prod- uct nowadays, especially high-speed and flex, and that is something I would recommend to designers. Holden: ere's a potentially big uptick in elec- tronics, which is good news for young engi- neers because there is plenty of job security. But the uptick means more complexity from the semiconductor guys and that doesn't nec- essarily make it easy for us. Kolmodin: I agree. It has grown leaps and bounds in the 35 years that I've been in this industry. With the acceleration of that curve, I imagine the next five or 10 years will be pretty amazing. Holden: Especially with electric vehicles. With electronics replacing all those mechanical transmissions, axles, and differentials, that's good news for fabricators and assemblers. But if you don't have the capital budget to keep up with it, that's bad news.