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Design for Surface Mount Technology Pin Assembly Disclosure Number: IPCOM000014558D
Original Publication Date: 1999-Oct-01
Included in the Prior Art Database: 2003-Jun-19

Publishing Venue


Related People

John Lauffer Robert Kulle William Brodsky David Russell


Disclosed is a Surface Mount Technology (SMT) pad design and structure to provide highly reliable soldered connections for high aspect ratio pins. High aspect ratio SMT pins are frequently used for the purpose of providing electrical communication and mechanical connection between "mother" and "daughter" PWB's. This disclosure is particularly useful in power supply circuits having a mother card fabricated on a metal substrate and also using non-reinforced dielectric layers. A cross sectional view of a typical, currently used, power supply card is shown in Figure 1, including a metal substrate (20), a non-reinforced dielectric layer (22), a copper SMT pad (24), a soldermask coating (26), reflowed solder (30) an SMT pin (50) and a daughter card (60). Assembly of this structure is achieved by screening a solder paste onto the power supply card, placing the pins and other components in the solderpaste, providing a temporary fixture board to hold the tops of the pins in the preferred locations, and finally reflowing the solderpaste to create the finished solderjoint. This design is subject to many potential problems due to the fulcrum effect forces that the long pin can exert on the base substrate. Particularly troublesome areas include handling damage that can occur by handling assemblies by the tops or sides of the pins, damage induced by removing the fixture board, or placing the daughter card on the tops of the pins, and particularly the later when the base substrate is still at an elevated temperature. The current pad design for a 0.072" diameter, 0.610" high pin is a 0.100" diameter Cu or Ni/Au plated Cu land having a 0.110" diameter soldermask opening surrounding it. Without implementation of critical process and handling controls at the pin assembly operation, a high occurrence of pin and pad delamination has been observed. The high occurrence is due to the fact that a minimal force applied to the top of the pin exerts tremendous strain at the base of the pin, leading to delamination at the weakest interface in the package. Additionally, the current pad design creates a temperature hot spot at the pad due to heat transfer through the pin during assembly processing. This hot spot can cause rapid degradation of the adhesive interfaces beneath the pad. In a first embodiment of the disclosed (Figure 2), the copper land has been increased to a minimum of 0.150" dimension, while maintaining the current 0.110" diameter soldermask opening. Increase of the copper pad may be made around the entire perimeter of the pad, or it may be done with extensions from the central pad (e.g. spokes of a wheel). This particular enhancement provides the following favorable aspects to improve reliability: