Printing materials circuit board design

Brist, Gary, and Long, Gary, Lead-Free Product Transition Impact on Printed Circuit Board Design and Material Selection, ECWC 10/APEX/IPC Conference, February 2005. 

Newer resins include polysulfone, polyethersulfone, polyetherimide, and polyetherketone. Some of these newer materials are high temperature thermoplastic, not thermoset, resins. They are being promoted for the design of injection-molded printed circuit boards in three-dimensional shapes for functional appHcations as an alternative to standard flat printed circuit boards. Only semiadditive or fully additive processing can be used with these devices. 

The need to evaluate alternatives often arises once the decision to eliminate chemicals of concern is made. Sometimes a chemical of concern can be eliminated through product design such as through the use of a material that is inherently flame retardant or a fabric barrier without the need for added flame-retardant chemicals. But when the only currently feasible option appears to be a chemical substitution, then the alternatives must be evaluated and assessed to ensure that they are in fact greener than the chemical they are intended to replace. We provide as examples of implementing alternatives assessment, the Green Screen for Safer Chemicals and the DfE Flame Retardants in Printed Circuit Boards Partnership. 

Fabrication of Devices and Materials. Many of the previously discussed applications of photopolymer technology have utilized photopolymer materials to manufacture a part that is then incorporated into commercial products (e.g. film resists used to manufacture printed circuit boards). One area that has been increasing very rapidly in the past 5-6 years has been the use of photopolymer chemistry to fabricate devices and materials that are used directly in the final product. This development has been made possible, in part, by the design of new photopolymer chemistry that can produce polymerized materials with enhanced physical properties. 

In a majority of cases, the thermoset/thermoset blends are actually formulated by the fabricator or the end user during the fabrication and processing of such materials as composite prepregs, printed circuit boards, laminates and adhesives. The formulations and compositions are often kept proprietary and are designed to meet their own individual requirements. 

The American ThermalWorks company has developed a new carbon fibre composite printed circuit board and substrate material, STABLCOR, which comprises a high temperature resin incorporating carbon fibre sandwiched between two very thin layers of copper. The material has a Tg of 170 "C. However, the company is developing a version with a Tg of 240 C. The material is designed as a plane , or non-signal carrying layer in a ply stack with other dielectric layers to make a composite PCB or device substrate. The carbon composite material has a dielectric constant of approximately 13.4 which makes it electrically conductive. This material allows the user to tailor the coefficient of thermal expansion of a PCB down to 3 ppm/°C to match that of silicon. 

IPC-2226 This specification educates users in microvia formation, selection of wiring density, selection of design rules, interconnecting structures, and material characterization. It is intended to provide standards for nse in the design of printed circuit boards utilizing microvia technologies. 

Have the appropriate stencil or screen design and materials (e.g., thickness, aperture geometry, wall finish, etc.) for the circuit board product. Design considerations must also address the need to widen fine-pitch aperture openings slightly for printing Pb-free solder paste. 

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