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14 The PCB Magazine • February 2016 high-speed optical fiber cables, and even extend- ing to bonding wire used for making intercon- nection between chip and package, the focus of this discussion will be on some of the enabling conductive materials the company has for the printed circuit industry. These materials serve a range of needs from circuit production, to alter- native layer-to-layer interconnection materials, to thermal via solutions, to EMI protection. Fol- lowing is a discussion of these different areas of application. Circuit Production Materials Circuits manufactured today are most often produced by a process that involves electroplat- ing copper circuits and plated-through-holes on a piece of copper-clad laminate and then etch- ing the circuit pattern. In contrast, Tatsuta set its sights on developing metal paste which can be screened or possibly jet-printed directly onto an insulating substrate to create the circuit pat- tern. The conductive paste is comprised of silver- coated copper particles, produced in a practical range of 3–5 µm size, evenly distributed into an epoxy resin/butyl carbitol base. The final product is 89% metal. The company has dem- onstrated the ability to print circuit features down to 100 µm line and space and the cure temperature is a modest 130°C (suitable for use with polyester base materials) resulting in con- ductors with a volume resistivity in the range of 1.0–2.0 x 10 -4 Ω˓cm. Finally, and not unimpor- tantly, the finished circuits have shown good solderability with common solder pastes. An example of a printed product is shown in Figure 1a and the same circuit pattern is shown with printed and reflowed solder on its lands in Fig- ure 1b. Further demonstration of the capabil- ity of the product is found in Figure 2 where full array solder-coated contacts with pitches of 0.65 mm, 0.5 mm and 0.4 mm are shown. Fi- nally, Figure 3 shows contacts for a peripherally leaded device to further evidence the fine fea- ture printing capability of the conductor paste. Via Fill Materials for Many Applications Metal pastes have and are serving a range of applications in today's high performance electronics. Those familiar with some of Japan's leading high density circuit manufacturing technology will appreciate how metal pastes have been used for interconnection of circuit features between metal layers. The two most common are B2IT solution and ALIVH (Any Layer Interstitial Via Hole) technologies. ALIVH new Material and proCess solutions for the eleCtroniC interConneCtion industry Figure 1: The printed paste is capable of resolving fine circuits features as illustrated in 1a; however, of equal importance, the printed metal is directly solderable as shown on the right, where Sn42Bi58 paste has been reflowed onto selected lands on the polyester base substrate. a b

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