Generally, solder can’t provide high-quality mechanical support. The strength of the plug-in itself is much larger than that of surface assembly. One is because the plug-in solder has a large cross-sectional area; the other is because the lead is inserted into the through-hole to provide mechanical support. Usually caused by the connector, there are thermal shock during the initial welding process, temperature cycling during operation, insertion force, twisting force and vibration force.
There are four key elements in designing connectors: lead structures, molding compounds, mechanical supports, and lead metal.
(1)Lead structure. The most important feature of the connector leads is their flexibility. Obviously, the flexible lead not only compensates for the coefficient of thermal expansion between the connector and the board, but also cushions the insertion stress. Both gull-wing and J-shaped pins are available. However, because the J-shaped pin structure bends the lead under the component body, such a connection point is difficult to measure visually. Currently, only a few connectors adopt this structure.
(2)Molding compound. Conventional thermoplastic materials have a lower melting point and are not suitable for surface assembly and reflow processes. High-temperature thermoplastic materials are suitable, but their high melting point increases craft difficulty and cost.
(3) Mechanical support. Except in a few cases, the connector should not be welded only count on the only mechanical support.A variety of shaft assisted support methods can be adopted. The connector can be mounted on the board by riveting, crimping, routing or screwing.
(4)Lead metal. In order to ensure sufficient soldering strength, the plating metal of the connector leads must have high solderability.Poor weldability not only causes problems during the production process, but also reduces the weld strength. The eutectic Sn-Pb coating provides the highest solderability, while the other coatings effecct are nearly similar.
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