Abstract Apparatus for fusing lead-tin platings provided upon printed circuit boards in a continuous process. The boards are moved by suitable conveyor means through a plurality of infrared energy sources provided on groups arranged on opposite sides of said boards and adapted to focus radiant energy to a line image, which plural line images sweep across and irradiate the boards as they pass through the locations of the radiant energy sources. The positioning between the radiant energy sources, the energy level and frequency spectrum of the sources and cooling thereafter is controlled so as to melt the matrix of lead and tin particles to flow together and form an alloy which is metallurgically bonded to the copper conductor while minimizing the propensity of the plating to flow into plated-through holes so as to partially or completely block such holes. In alloy platings of greater than 1 mil thickness an ''''airknife'''' is provided immediately adjacent the last heating source on either or both sides of the board to produce a precipitous temperature drop from the flow temperature to a temperature slightly above the freeze point to reduce fluidity and mobility of the alloy especially in the region of plated-through holes.
Apparatus for alloying and bonding a solder type of plating previously applied to the conductive surfaces of printed wiring boards comprising: a conveyor for supporting and conveying the printed wiring boards along a linear path; means for moving said conveyor at a predetermined rate; first radiant energy heating means for directing radiant energy toward one side of said conveyor to create a first heating zone; second radiant energy heating means for directing radiant energy toward the other side of said conveyor to create a second heating zone; said conveyor being of an open structure to permit passage of said radiation to that side of said printed wiring board contacting said conveyor; said first and second radiant energy heating means being adapted to direct the radiant energy in each of their associated zones upon the opposing surfaces of said boards as they pass between said first and second radiant heat zones to heat said plating to a temperature sufficient to cause said plating to form an alloy and bond said alloy upon said printed wiring board conductive surfaces; cooling means positioned immediately following said heating zones for directing moving air upon at least one surface of said boards; said heating means each being comprised of a source of radiant energy lying within the visible and near infrared wavelengths; reflector means for directing radiation from said source and impinging upon said reflector upon an associated suRface of said printed wiring board.
Claim 2
Dependent Claim
239 words
Apparatus for alloying and bonding a solder type of plating previously applied to the conductive surfaces of printed wiring boards comprising: a conveyor for supporting and conveying the printed wiring boards along a linear path; means for moving said conveyor at a predetermined rate; first radiant energy heating means for directing radiant energy toward one side of said conveyor to create a first heating zone; second radiant energy heating means for directing radiant energy toward the other side of said conveyor to create a second heating zone; said conveyor being of an open structure to permit passage of said radiation to that side of said printed wiring board contacting said conveyor; said first and second radiant energy heating means being adapted to direct the radiant energy in each of their associated zones upon the opposing surfaces of said boards as they pass between said first and second radiant heat zones to heat said plating to a temperature sufficient to cause said plating to form an alloy and bond said alloy upon said printed wiring board conductive surfaces; cooling means positioned immediately following said heating zones for directing moving air upon at least one surface of said boards; said heating means each being comprised of a source of radiant energy lying within the visible and near infrared wavelengths; reflector means for directing radiation from said source and impinging upon said reflector upon an associated suRface of said printed wiring board.
Claim 3
Dependent Claim
34 words
The apparatus of claim 1 wherein said cooling means further comprises a narrow, elongated outlet opening for constraining the air passing therethrough into a narrow, elongated zone positioned immediately behind the last heating zone.
Claim 4
Dependent Claim
46 words
The apparatus of claim 2 wherein said outlet opening is aligned so as to cause air passing through said outlet opening to move in a direction diagonally aligned with the surface of the boards so as to direct heat and fumes away from said heating zones.
Claim 5
Dependent Claim
74 words
The apparatus of claim 2 wherein said cooling means is adapted to include means for moving air through said outlet opening at a velocity sufficient to rapidly cool each board passing through the cooling zone to a temperature level slightly above the freeze point of the plating composition to reduce the mobility of the compostion to a degree sufficient to prevent the composition from flowing into and filling plated-through holes provided in the boards.