Method for manufacturing printed circuit board assembly

• US 6,226,862 B1
• Filed: 04/30/1998
• Issued: 05/08/2001
• Est. Priority Date: 04/30/1998
• Status: Expired due to Term

• Current Assignee: Flex, Ltd.
• Original Assignee: Sheldahl, Inc.
• Inventors: Neuman, David
• Primary Examiner(s): Huson, Gregory L.
• Assistant Examiner(s): Chang, Rick Kiltae
• Application Number:
  US09/070,505
• Time in Patent Office: 1,104 Days
• Field of Search: 29/830, 29/840, 29/843, 174/264, 174/263, 219/605, 219/616, 219/633, 156/290, 156/292
• US Class Current: 29/830
• CPC Class Codes: H05K 2201/10977 Encapsulated connections
• CPC Class Codes: H05K 2203/101 Using electrical induction, e.g. for heating during soldering
• CPC Class Codes: H05K 3/305 Affixing by adhesive
• CPC Class Codes: H05K 3/3473 Plating of solder
• CPC Class Codes: H05K 3/3494 Heating methods for reflowing of solder using integral heating means H05K1/0212
• CPC Class Codes: H05K 3/361 Assembling flexible printed circuits with other printed circuits
• CPC Class Codes: H05K 3/363 by soldering
• CPC Class Codes: H05K 3/386 by the use of an organic polymeric bonding layer, e.g. adhesive
• CPC Class Codes: Y10T 29/49126 Assembling bases
• CPC Class Codes: Y10T 29/49144 by metal fusion
• CPC Class Codes: Y10T 29/49149 by metal fusion bonding

Abstract

Disclosed is a new process for electrically and mechanically joining arrays of conductors on flexible printed circuits and other flexible conductors including collated flat, flexible cables (FFCs). An array of flat copper conductors on a flexible dielectric sheet is electroplated with tin-lead solder. Surface insulation is locally omitted or removed from conductor surfaces. A second circuit or cable is overlapped in competent electrical communication and the solder plating fused by inductively heating the copper to join the two conductor arrays. An adhesive placed between conductors is also thermally activated to bond the film on the two cable arrays together. This insulates the electrical connections and seals them from attack by moisture and chemical pollutants.

Claims

1. A method for connecting a first flexible film circuit board to a second flexible film circuit board, each of the boards having mated, solder covered copper leads disposed on the circuit board and adhesive disposed between the leads, comprising steps of:

contacting the mated, solder covered leads of the first fleexible film circuit board with the mated, solder covered copper leads of the second flexible film circuit board;

inductively soldering the leads of the first board to the leads of the second board; and

bonding the adhesive disposed between the leads of the first board to the adhesive disposed between the leads of the second board, wherein sufficient pressure is placed on the first and second boards to create an electrical connection and an adhesive bond and creating a lap-joint wherein adjacent pairs of mated leads are sealed from one another with no short circuit.

2. The method of claim 1 wherein the bonding step further comprises a step of applying pressure to the lap-joint such that a portion of the first board has a shape that conforms to contours of a portion of the second board to enhance seal bonding between the leads.

3. The method of claim 1 wherein the inductive soldering further step includes steps of:

disposing the first board on a vacuum table; and

covering the lap-joint with a sheet of flexible plastic that will withstand a temperature of about 200°

C., the sheet also disposed on the vacuum table lateral to sides of the lap-joint.

4. The method of claim 1, wherein the bonding step includes applying heat to the lap-joint to activate the adhesive.

5. The method of claim 1 wherein the first and second flexible films comprise a polyester film and the pressure on the first and second boards is less than 15 psi.

7. The method of claim 5 wherein the polyester film comprises a group consisting of polyethylene-terephthalate film and a polyethylene-naphthalate film.

8. The method of claim 5 wherein the polyester film substrate has a thickness of about 25 to 175 microns.

6. A method for connecting a first flexible circuit board to a second flexible circuit board, each of the boards having mated, solder covered copper leads disposed on the circuit board and thermally activated adhesive disposed between the leads, comprising steps of:

contacting the mated, solder covered copper leads of the first flexible film circuit board with the mated, solder covered copper leads of the second flexible film circuti board;

inductively soldering the leads of the first board to the leads of the second board; and

heating the adhesive under pressure where in the adhesive disposed between the leads of the first board is bonded to the adhesive disposed between the leads of the second board, thereby creating a lap joint wherein adjacent pairs of mated leads are sealed from one another.