Solderability of Coatings for Printed Circuits

Abstract

Solderability of a selection of coatings on copper foil, stored under various conditions, has been determined using both the minimum wetting-time test and area of spread tests. Pure tin and tin-lead alloy plated coatings about 0·3 mils thick withstand all the storage treatments with no loss in solderability. A flash of gold over the same thickness of tin-nickel alloy plating was next in order of merit. 0·2 mils of various alloy gold coatings lost solderability under some conditions but in any case caused embrittlement of the solder, thus confirming other work. A brittle bond was also obtained with a thick palladium coating. All of the very thin metallic coatings, the lacquer film and the chemical preservative treatment, allowed a serious loss of solderability during storage. The results are considered to be of direct application in the electronic industry, especially in the field of printed circuitry and it is suggested that the wetting-time test gives the most accurate assessment of solderability for printed circuit material.