PROCEDE DE TRAITEMENT PAR EVAPORATION SOUS VIDE DE PLAQUETTES ACIRCUITSIMPRIMES

摘要

Relates to the avoidance of electrical discontinuities arising in the production of two-sided printed circuit boards having plated-through-holes and particularly occurring in the use of solder for improving the electrical interconnections. Research disclosed that the cause of these discontinuities lay in the material of the boards surrounding the holes which either included entrapped gas or matter vaporizable under the high temperatures of the liquid solder applied to fill the holes and which impaired the attainment of reliable plated-through-hole connections. A vacuum evaporation operation is incorporated in the fabrication process and found highly useful and efficient in the production of reliable hole connections substantially reducing if not completely eliminating any need to apply solder touch-ups to the boards thereafter. Specifically, the boards are treated prior to the soldering of the plated-through holes to a temperature of approximately 250 DEG F while concurrently being exposed to a vacuum of approximately 10<->2 mm Hg for a sufficient time to drive out of the boards all matter vaporizable under such conditions. In carrying out this vacuum-heat treatment operation, inert gas is initially used in the treatment chamber to hasten the heating of the boards following which the chamber is exhausted of the gas and subjected to high vacuum while maintaining the temperature to which the boards have been raised. In returning the heat treatment chamber to normal room conditions, an inert gas may be re-introduced into the chamber to hasten the cooling of the circuit boards. When there will be an elapse of time before the soldering operation is performed, the de-gassed circuit boards are preferably placed in sealed containers or bags to prevent contact with the atmosphere and the resultant absorption of moisture and deleterious gasses therefrom.