2007 Issue

UTAH ENGINEERS COUNCIL JOURNAL 31 circuits, the integration of many transistors on one semiconductor substrate (i.e., chip). Bob Noyce at Fairchild and Jack Kilby at Texas Instruments independently invented the integrated circuit (IC) beginning in 1959. The IC was packaged in the dual inline package (DIP) that was invented by Bryant Rogers. The DIP was a rectangular ceramic (typically alumina) sandwich with the silicon chip in the middle of the assem- bly equipped with small bonding pads on the silicon chip connected to thin gold wires which were, in turn connected to a brass, spider-like lead frame that ran through the middle of the two ceramic layers and formed pins outside the package (which could be inserted through holes in a printed wiring board to work as a circuit element). The two ceramic layers were fastened together at high temperature by a glass frit. The ceramic DIP (CERDIP) package was hermetic, like the TO package. Companies began to exploit market opportunities using the transistor in the TO and the IC in the CERDIP. However, the cost of the CERDIP package was often more than the IC itself. Therefore, begin- ning in the 1970s, ICs were encapsulated in plastic molding compounds. Plastic offers useful benefits of being low cost and easy to form, but polymers, by their structure, permit moisture to move between their large polymeric chains. The moisture caused additional reliability issues, the absorbed moisture formed steam during soldering that resulted in explosive delamination called, appropriately, “popcorning.” Today most ICs are available packaged in plastic due to advances in molding compounds and die passivation. As IC complexity demanded more interconnect pins, around 1980 another IC technology roadblock loomed. The leaded package geometry could not offer as many pins (or input/output, I/O) as the ICs required. Efforts to add more pins brought about a new printed wiring component mounting called surface mount technology IEEE — continued (SMT). SMT eliminated the need to drill through the PWB. Instead, the components were soldered to the surface. Immediately, this freed up both sides of the PWB, making more area for mounting SMT components. However, surface mounting created shear loads on the solder joints, and the joints were prone to failure from normal tempera- ture cycling. Much work ensued on solving this solder problem, initially under the aus- pices of IEEE’s efforts such as the Compliant Lead Task Force (and other organizations such as the American Society of Mechani- cal Engineers Electronics Packaging and Production Division). SMT solved the I/O problem by introducing the ball grid array (BGA) package. The ball grid array uses the solder ball solder surface tension to locate the package on the PWB and provides hundreds of I/O. Today the BGA concept has been extrapolated to simpler packages such as “flip chip;” flip chip refers to having the chip inverted and the active circuit side soldered directly to the PWB with a poly- meric fill between the PWB and the chip to help carry mechanical loads. The microelectronics story, although richer than this brief introduction can cover, is far more than just the story of solid state devices or their packages. One of the fascinating lesser-known stories behind microelectronics is the story of the evolution of passive components that make microelectronics practical. Passive components include connectors, resistors, inductors, and capacitors. As a rule of thumb, passives account for 80% to 99% of the components. A desktop computer has approximately 2800 passive components. The most common component in modern digital electronics is the ceramic capacitors. The world market for ceramic capacitors is roughly ten trillion per year. The body of most ceramic capacitors used in commercial electronics is made up of barium titanate (BaTiO3). Barium titanate is an unusual material with 4 phases. It is the tetragonal phase that is most useful due to polarization from its “rattling tita- nium” atom. As a capacitor dielectric, it is doped to provide best performance at room temperature and to enhance stability. The high dielectric constant of barium titanate was discovered during World War II. Dur- ing the war, the properties were studied by Arthur von Hippel and his staff at the Laboratory for Insulation Research at MIT. As a result, Professor von Hippel has been called the first molecular engineer by one of his students, Pennsylvania State University Professor Emeritus Newnham. I disassembled my old cell phone (2002 model) as an example of modern electron- ics. Figure 1 is a photo of the keyboard side. The PWB uses gold plating. The round pads are keyboard contacts. Electrical compo- nents include connectors, tantalum and ceramic capacitors (most of the parts), chip resistors, light emitting diodes and several ICs. Figure 2 is approximately an 0.8 in2 region around a BGA on the backside of the PWB. If this were a more modern cell phone, it would likely have fewer ICs due to added integration on each chip and more passives embedded into the PWB, but the phone would also have more features includ- ing multiple bands and a video camera. Since NSPE started EWeek over 55 years ago, electronics technology has con- tributed greatly to mankind. Like all great accomplishments, there are many engineers and scientists who worked to contribute to this progress. Only by recognition of the grand contribution of all our engineering colleagues, past and present, can we go for- ward to form the personal relationships that create meaningful collaboration to answer the myriad human needs of a growing world population in the 21st century. Dr. Gordon Moore invented Moore’s Law which says that the number of transistors on an integrated circuit would double every two years. Arsdell, J., Electric Circuit Assembly, U.S Patent 2607821, 19 August 1952.