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Soldering The button rectifier is basically a semiconductor chip bonded between two nickel-plated copper heat sinks with an encapsulating material of epoxy compound. The exposed metal areas are also tin plated to enhance solderability. In the soldering process it is important that the temperature not exceed 260IC if device damage is to be avoided. Various solder alloys can be used for this operation but two types are recommended for best results: 1. 95% Sn, 5% Sb; melting point 237IC 2. 96.5% tin, 3.5% silver; melting point 221IC 3. 63% tin, 37% lead; melting point 183IC Solder is available as preforms or paste. The paste contains both the metal and flux and can be dispensed rapidly. The solder preform requires the application of a flux to assure good wetting of the solder. The type of flux used depends upon the degree of cleaning to be accomplished and is a function ofthe metal involved. These fluxes range from a mild rosin to a strong acid; e.g., Nickel plating oxides are best removed by an acid base flux while an activated rosin flux may be sufficient for tin plated parts. Since the button is relatively lightweight, there is a tendency for it to float when the solder becomes liquid. To prevent bad joints and misalignment, it is suggested that a weighting or spring loaded fixture be employed. It is also important that severe thermal shock (either heating or cooling) be avoided as it may lead to damage of the die or encapsulant of the part.