Optimization of lead free solder 01005 component assembly

Abstract

PurposeTo optimize the printed circuit board design and assembly processes to minimize defects in the assembly of 01005 size chip resistors.Design/methodology/approachA test board was designed with a range of pad sizes, pad shapes, pad spacings and pad orientations. This test board was used in a series of designed experiments to optimize the printing, placement and reflow processes. Assembly defects were analyzed as a function of board design and assembly processes.FindingsAn electroformed, 76 μm stencil yielded a robust paste printing process and higher process capability indices (Cp) compared to a 102 μm stencil. Nitrogen reflow was required to achieve good solder wetting due to the high surface‐to‐volume ratio of the solder deposits. With regard to bridging defects, no defects were observed if the pad‐to‐pad spacing for parallel resistors was 150 μm or larger. Rectangular pads with no vias‐in‐pad and designed at 90 percent of nominal pad size (pad size type 2) with the ramp profile, independent of 0° or 90° resistor orientation yielded the lowest number of defects. Given the undersized pads on the actual board, the 90 percent pad average width was 170 μm (versus a design value of 183 μm) and the measured width of the 01005 chip resistor was 180 μm. Thermal cycle reliability testing of the solder joints with this pad size showed no failures after 1,000 thermal cycles.Originality/valueThe results of this work provide a set of design and assembly processes recommendations for those who must implement 01005 size component assembly in production.