A. lthough Sumitomo Wiring Systems, Ltd. has already been supplying "the First Generation Press-fit Connector" for the European customer from 2004, it has had a limited throughhole diameter tolerance range of only 90ptm and this has been the major cause of difficulty in adoption for many other customers, including domestic.
Therefore we have started the development of "the Second Generation Press-fit Connector", which has been adaptable to a wider through-hole diameter tolerance range, in anticipation of a larger market in the near future.
B. Applicationfor Automobile Connectors For the application of press-fit connection technology to automobile connectors, we had to take into consideration certain specific factors, as listed below.
(1) Long Term Connection Reliability in the more severe environmental conditions required for automotive connectors.(Exposed to Vibration, Mechanical and Thermal Shocks etc.)
(2) Lower Cost, at least equivalent to that of a conventional flow soldering process.
(3) Adaptation to wider through-hole diameter tolerance ranges.
(4) Connection Reliability for the various PCB surface treatments.
Statement (4) means that various surface treatments, like "Immersion Plating (tin or silver)" and "Organic Solderability Preservative (OSP)" have been recently developed and adopted for preventing the oxidization of copper surfaces on PCB as alternatives to the conventional HASL (Hot Air Solder Leveling) [2].However, these surface treatments may affect the press-fit connection reliability, because the surface treatments on PCB come into direct contact with terminals.
II. DESIGN GUIDELINES
A. Specification Summary
The specification of the press-fit connector we developed is summarized in Table II.
In Table II, "Size" means the male contact width (the socalled "Tab Size") in mm.
B. Appropriate Contact Force Range Determination As the first step of press-fit terminal design, we must determine the appropriate range of contact force.
For this purpose, the deformation characteristic diagrams of terminals and through-holes are drawn schematically, as shown in Fig. 2. It is indicated that contact forces are in a vertical axis,while terminal sizes and through-hole diameters are in the horizontal axis respectively.
Two lines for the terminal deformation mean ones for maximum and minimum terminal sizes due to dispersion in manufacturing process respectively.
Table II Scecification of the Connector we develored
It is clear that the contact force generated between terminals and though-holes is given by the intersection of two diagrams for terminals and through-holes in Fig. 2, which means the balanced state of terminal compression and throughhole expansion.
We have determined
(1) the minimum contact force required to make the contact resistance between terminals and though-holes lower and more stable before/after the endurance tests for the combination of minimum terminal sizes and maximum through-hole diameter, and (2) the maximum force sufficient to ensure the insulation resistance between adjacent through-holes exceeds the specified value (109Q for this development) following the endurance tests for the combination of maximum terminal sizes and minimum through-hole diameter, where the deterioration in insulation resistance is caused by the moisture absorption into the damaged (delaminated) area in PCB.
In the following sections, the methods used to determine the minimum and maximum contact forces respectively.
Post time: Dec-07-2022