| Embedded Active Components for High-Reliability Products |
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| Written by Jim D. Raby | |||
| Thursday, 31 January 2008 19:00 | |||
The missile’s shock and vibration mandated a new technology: a wire-bonded, solderless PCB.I never planned to be in the assembly and manufacturing business. I was satisfied with my life in government, working with high reliability hardware, including various weapons systems and the Saturn Apollo program – the beginning of my industry experience. That is where I learned the most about the effects of vibration and shock on components and PCBs. But time has a way of changing one’s direction. One day, a friend who worked for the U.S. Navy called and asked for my help on a failing circuit board. I visited the supplier, provided a short-term solution, and then gave the Navy a plan for a long-term solution. They jumped on it quickly.The problem was, the Navy supplier was mounting a heavy module on the board surface. When fired in the missile, the module leads would break loose and fail. Several companies have successfully buried passive die and components in boards, but many attempts to do the same with active die had failed. Nevertheless, I concluded that was the solution to the Navy’s problem. I planted the seed with some bright, young engineers who did not know it “wasn’t possible.” Here’s what we developed. We built wire bonds from chip to board, forming a shorter circuit path, hence fewer parasitic influences. (Store the bare die in a nitrogen environment within a clean room.) The process does not use solder; therefore, tin whisker problems have been eliminated. After assembly is completed, so-called step cavities are filled with suppression materials and then covered with a copper lid on each side. The unit is now a solid block of electronics. There are flex tail inputs and outputs that permit connections to adjacent systems. A central cooling core in the board dissipates heat from components – more so than had been previously capable. For denser packaging, die can be stacked within the cavities. A major problem was finding a board shop and tooling to build the boards, as the step cavities are not simple to build. The result: complex hardware in about one-third the previous printed circuit board area.  In October 2006, after sufficient testing to satisfy the harshest skeptics, we were issued US patent 7,116,557. Assemblies built using the novel process have withstood long temperature and humidity testing, and we know it to be solid manufacturing technology. It is less expensive to build with new designs, and it eases the weight and size of electronics modules. And we have had a successful Navy missile flight, and have built gun launch modules to withstand more than 20 kg of shock without failure. Ed.: US 7,116,557, “Imbedded Component Integrated Circuit Assembly and Method of Making Same,” covers a printed circuit board assembly comprising a primary core of thermally conductive material; a two-tiered laminate substrate connected to the primary core, the two-tiered laminate substrate including a two-tiered cavity and electrically conductive circuit bonding pads connected to a circuit imbedded in a lower tier of the two-tiered laminate substrate; a circuit component disposed within the two-tiered cavity and connected to the primary core using a thermally conductive adhesive material, the circuit component including electrically conductive component bonding pads; flexible electrical interconnects connected to the electrically conductive circuit bonding pads and the electrically conductive component bonding pads; a conformal coating covering portions of the two-tiered laminate substrate, the thermally conductive adhesive material, the circuit component, the electrically conductive component bonding pads, the flexible electrical interconnects, the electrically conductive circuit bonding pads, and any portions of the primary core located in the two-tiered cavity and not covered by the thermally conductive adhesive material; and an encapsulating material filling the two-tiered cavity and encapsulating the thermally conductive adhesive material, the circuit component, the electrically conductive component bonding pads, the flexible electrical interconnects, and the electrically conductive circuit bonding pad. To review the patent, visit http://cc.msnscache.com/cache.aspx?q=72375698744183&lang=en-US&w=e65f8287. Jim D. Raby, PE, is founder of Soldering Technology International (STI Electronics Inc.) (stielectronicsinc.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
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Columns
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