Industry Historian Takes Exception to Flip-Chip's Birthday Your July issue (page 32) suggests that flip chip was born in Detroit 32 years ago. We at SMTA suggest that the date was earlier, the birthplace was New York and the baby had better parentage. A few months ago, SMTA focused on flip chip during a conference in Boston, MA. Our Flip Fest featured tutorials, papers and a lively panel discussion. But there was also a contest that asked the audience to guess the official birthday of Flip Chip. Since just about everyone recognizes IBM as the inventor, we asked the Endicott, NY, group to provide an official birthday. We wanted a documented date, not a recollection. Flip chip pioneer, Dr. Paul Totta (Dr. Flip Chip to us) came up with August 1, 1961 as the first time that flip chip was officially presented in a meeting. Work was certainly going on much earlier in the labs, but we wanted a launch date rather than the date of invention. Dr. Totta also provided drawings and photos of early flip chips that are shown above. The revolutionary IBM product was the SLT, or Solid Logic Technology (Figure 1), that Harvey Miller's article referred to as the precursor to flip chips. But we contend that the SLT was a genuine flip chip. In fact, the SLT is very likely the first CSP! But let the readers judge based on the information provided by IBM. The SLT is a direct chip attach (DCA) design that used copper (Cu) micro-spheres from Alpha Metals to create the joints. Today, Alpha Metals (now Alpha-Fry TechnologiesÐCookson) gets many requests for Cu spheres because this is still a good idea. The copper BGA system can enable easy testing and rework. Unlike soft solder bumps, the harder copper spheres can be easily probed, clamped or plugged into burn-in sockets. What's more, since the Cu balls are attached to the chip with high-melting alloy, the SLT can be removed and replaced without the common "reballing" process required for many BGAs. Protected by Passivation Layers The chip is well protected by inorganic passivation layers and does not use encapsulation. The assembled package is robust with NO underfill required. The copper interconnect structure boosts strength and improves electrical performance. Solders generally have much higher volume resistivity than copper. Lower resistance paths have become increasingly desirable as frequency is pushed ever higher. Billions of SLTs went into 360 mainframes and other great computers that set an incredible reliability record, perhaps the best ever. The 40-year-old SLT may be the first SMD, minimal package, BGA and CSP. The copper balling process was eventually replaced by solder-based Controlled Collapse Chip Connection (C4, actually C4) around 1964. A photo of one of the early solder-bumped flip chips is shown in Figure 2. So, is the SLT a flip chip? Is it a CSP? Whatever the SLT was, it's still a great idea 40 years later. Sincerely, Dr. Ken Gilleo, Cookson Electronics Harvey Miller replies: In matters of packaging history, I will always defer to Ken Gilleo. No Layoffs at STATS I read your salary survey article in the August-September issue, where you mention that STATS was one company that has had layoffs. It is true that STATS has undergone cost-cutting measures and mandatory vacation time, but we have not laid off any full-time employees. Our CEO has held very strongly to the belief that it is important to keep the employees in place so that we can be positioned to take advantage of the eventual turn in the industry. With natural attrition, the company has looked very closely at what positions should or should not be replaced at the present time, but STATS has not had layoffs anywhere in the organization. Since STATS has worked very hard not to lay off employees, we would very much like to set the record straight. Lisa Lavin [lavinl@statsus.com] Chip Scale Review regrets the error.
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