Method of attaching a flexible printed circuit board to a rigid printed circuit board

• US 3,926,360 A
• Filed: 05/28/1974
• Issued: 12/16/1975
• Est. Priority Date: 05/28/1974
• Status: Expired due to Term

• Current Assignee: Unisys Corporation
• Original Assignee: Douglas E. Jr. Moister
• Inventors: Moister, Douglas E. Jr.
• Primary Examiner(s): Smith, Al Lawrence
• Assistant Examiner(s): Watson, Robert C.
• Application Number:
  US05/473,698
• Time in Patent Office: 567 Days
• Field of Search: 29/471.1,488,489,493,495,498,502,628 228/179,180,212,223,240,248,254
• US Class Current: 228/180.21
• CPC Class Codes: B23K 1/0053 soldering by means of I.R.
• CPC Class Codes: B23K 2101/42 Printed circuits
• CPC Class Codes: H01R 12/62 connecting to rigid printed circuits or like structures
• CPC Class Codes: H05K 2201/09572 Solder filled plated through-hole in the final product soldering lead-in-hole components H05K3/3447
• CPC Class Codes: H05K 2201/10666 Plated through-hole for surface mounting on PCB
• CPC Class Codes: H05K 2203/041 Solder preforms in the shape of solder balls soldering leadless components having an array of bottom contacts H05K3/3436
• CPC Class Codes: H05K 2203/0455 PTH for surface mount device [SMD], e.g. wherein solder flows through the PTH during mounting
• CPC Class Codes: H05K 3/3494 Heating methods for reflowing of solder using integral heating means H05K1/0212
• CPC Class Codes: H05K 3/363 by soldering

Abstract

An improved method for soldering the terminals of a rigid printed circuit board to those of a flexible printed circuit board, such method comprising the steps of focusing a radiant heating source upon each of a plurality of solder globules deposited in a like number of through holes in the terminals of the rigid printed circuit board for controlling of the capillary flow of the molten solder radially from the through holes to form solder points of controlled depth and pattern between the terminals of the boards.

Claims

1. A method for solderably joining a selected terminal of a flexible printed circuit board to a selected terminal of a rigid printed circuit board comprising the steps of:

a. providing one or more apertures in the rigid printed circuit board through its said selected terminal, b. plating the surfaces of said selected terminals, c. pre-heatably filling each of said apertures with a globule of solder of sufficient size to produce a protruding convex upper and lower meniscus thereof as a byproduct of said plating, d. bringing the selected terminal of said flexible printed circuit board into compressible contact with each of said lower convex meniscuses of solder in the apertures of said rigid printed circuit board, e. arranging an infrared heating source and focusing means therefor in aligned focusing relationship relative to each of said upper meniscuses of solder, and f. controllably activating each of said infrared heating sources such that an infrared beam of controlled intensity and timeduration is directed upon each of said upper convex meniscuses to bring each of said solder globules to a molten state and to thereby capillarily transform each of said lower convex meniscuses to a radially formed solder joint between said selected terminals when said molten solder solidifies.

2. The method defined in claim 1 wherein the step of controllably activating more than one of said infrared heating sources is preceded by the step of supportably and evenly backing said flexible Printed circuit board on the side thereof opposite the selected terminal thereof, such that each of said radially formed solder joints between said selected terminals is of uniform depth.

3. The method defined in claim 1 wherein the step of bringing the selected terminal of the flexible printed circuit board into compressible contact with each of the lower convex meniscuses of solder in the apertures of the selected terminal of the rigid printed circuit board comprises the steps of:

a. registering the selected terminals together in overlapping relationship, b. compressibly backing said flexible printed circuit board on the side thereof opposite its said selected terminal, and c. clamping the printed circuit boards together such that the selected terminals are retainably aligned in said overlapping registration.

4. The method defined in claim 1 wherein the step of controllably activating each of the infrared heating sources includes the steps of:

a. focusing a beam from said heating source upon the upper convex meniscus of solder with which said heating source is aligned, and b. controlling the intensity and time duration of said infrared beam for maximum dispersion of the molten solder from the lower end of each of the solder filled apertures to form radial patterns via capillary flow intermediate said selected and registrationally aligned terminals.

5. A method for solderably joining the substantially planar terminals of a flexible printed circuit board to the substantially planar terminals of a rigid printed circuit board comprising the steps of:

a. forming one or more apertures in the rigid printed circuit board through each of its said terminals, b. plating the terminals of the flexible printed circuit board and the rigid printed circuit board, and the walls of the apertures formed in the rigid printed circuit board, c. depositing a globule of solder in each of the apertures in the terminals of the rigid printed circuit board as a byproduct of said plating of the terminals, d. bringing the terminals of the flexible printed circuit board into firm contact with the terminals of the rigid printed circuit board such that they are prepositioned in overlapping registry with each other, e. supportably presenting a resilient back pad to the flexible printed circuit board on the side thereof opposite its said terminals, and f. controllably focusing radiant heat locally upon the exposed sides of the globules of solder in each of the apertures formed in the terminals of the rigid printed circuit board for enabling the molten solder to capillarily flow between the registered terminals to radially form corrsponding solder joints therebetween.

6. A method of solderably bonding the plated terminals of a flexible printed circuit board to the plated terminals of a rigid printed circuit board comprising the steps of:

a. forming at least one aperture through said rigid printed circuit board at each of its said plated terminals;

b. depositing a globule of solder in each of said apertures;

c. aligning the plated terminals of said flexible printed circuit board with the solder-containing apertures of the corresponding plated terminals of said rigid printed circuit board;

d. applying a predetermined amount of pressure to the side of said flexible printed circuit board not in contact with the plated terminals of said rigid printed circuit board to insure a uniform depth of the solder joint; and

e. locally applying a predetermined controlled amount of radiant energy to the side of each of said solder globules not in contact with the plated terminals of said flexible printed circuit board for effecting a capillary flow of solder into a radially patterned solder bond of a uniform dispersion and depth at each of the points of contact between the plated terminals of said flexible printed circuit board and the corresponding apertured plated terminals of said rigid printed circuit board.

7. The method of claim 6 wherein said step of depositing a globule of solder in each of said apertures includes the step of preheatedly depositing a molten globule of solder in each of said apertures and forming a convex lower surface of said globule which protrudes out of said aperture for contacting said corresponding plated terminals of said flexible printed circuit board.