Solder joint structure of flexible printed circuit board

• US 10,165,690 B2
• Filed: 06/17/2016
• Issued: 12/25/2018
• Est. Priority Date: 06/19/2015
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Usui, Mitsuo, Kikuchi, Kiyofumi, Tsuzuki, Ken, Fukuda, Hiroshi, Asakawa, Shuichiro, Kamei, Shin, Soma, Shunichi, Saida, Takashi
• Primary Examiner(s): Chen, Xiaoliang
• Application Number:
  US15/735,726
• Publication Number:
  US 20180199445A1
• Time in Patent Office: 921 Days
• Field of Search: 174263, 174260, 174261, 174264, 257434, 257693, 257698, 257724
• CPC Class Codes: H05K 1/0269 for visual or optical inspection
• CPC Class Codes: H05K 1/11 Printed elements for providing electric connections to or between printed circuits
• CPC Class Codes: H05K 1/111 Pads for surface mounting, e.g. lay-out
• CPC Class Codes: H05K 1/117 Pads along the edge of rigid circuit boards, e.g. for pluggable connectors
• CPC Class Codes: H05K 1/14 Structural association of two or more printed circuits providing electric connection to or between printed circuits H05K1/11, H01R12/00
• CPC Class Codes: H05K 1/147 at least one of the printed circuits being bent or folded, e.g. by using a flexible printed circuit H05K1/148 takes precedence
• CPC Class Codes: H05K 1/189 characterised by the use of a flexible or folded printed circuit H05K3/326 takes precedence
• CPC Class Codes: H05K 2201/09181 Notches in edge pads
• CPC Class Codes: H05K 2201/09409 Multiple rows of pads, lands, terminals or dummy patterns; Multiple rows of mounted components
• CPC Class Codes: H05K 2201/10121 Optical component, e.g. opto-electronic component
• CPC Class Codes: H05K 3/3463 Solder compositions in relation to features of the printed circuit board or the mounting process
• CPC Class Codes: H05K 3/36 Assembling printed circuits with other printed circuits H05K7/142 takes precedence
• CPC Class Codes: H05K 3/363 by soldering
• CPC Class Codes: H05K 3/403 Edge contacts; Windows or holes in the substrate having plural connections on the walls thereof H05K3/4092 takes precedence

Abstract

In a conventional soldering method, an FPC-side electrode pad and a package-side electrode pad are closely joined together with a solder layer, and the soldered state after a joining process has not been easily confirmed visually. The present invention provides a solder joint structure including a side face electrode which is formed on each of the side faces of the end parts of an FPC board and a package or PCB board that are to be soldered, extending vertically relative to the faces constituting each of electrode pads on the boards, and which introduces solder. On the side face electrodes of the board end parts, a part of solder that is formed continuously from the solder joint portion is visible and the state of the solder joint between the electrode pads on the two boards can be confirmed. The efficiency of solder joint tests can be improved.

Claims

1. A solder joint structure connecting a first board composed of a first material having flexibility and a second board composed of a second material that is different from the first material, wherein:

the first board includes a plurality of electrode pads formed along an end part of the first board, each of the plurality of electrode pads includes two corresponding conductive electrodes having generally the same shape on both faces sandwiching the first board, the two corresponding conductive electrodes are mutually connected by at least one through hole, the two corresponding conductive electrodes, including an inner part of the through hole, have a solder layer formed thereon, and the two corresponding conductive electrodes are further mutually connected by a side face electrode formed on a side face of the end part of the first board;

the second board includes a plurality of electrode pads formed along an end part of the second board to face the conductive electrodes on one face of the first board; and

the conductive electrodes on the one face of the first board and the plurality of facing electrode pads on the second board are solder joined with the solder layer, and the solder joint is configured such that a joined state of a soldered portion on the side face electrode formed continuously from the solder joint is visible from the second board side of the solder joint.

2. The solder joint structure according to claim 1, wherein

the second board includes a side face electrode formed continuously from the plurality of facing electrode pads on the second board onto a side face of the end part of the second board, and the solder joint is configured such that a joined state of a soldered portion on the side face electrode formed continuously from the solder joint is visible from the first board side of the solder joint.

3. The solder joint structure according to claim 1, wherein the side face electrode of the first board is formed by cutting a through hole, which pierces the first board, in a vertical direction with respect to a face of the first board.

4. The solder joint structure according to claim 2, wherein the side face electrode of the first board is formed by cutting a through hole, which pierces the first board, in a vertical direction with respect to a face of the first board.

5. The solder joint structure according to claim 1, wherein

the plurality of electrode pads of the first board and the plurality of facing electrode pads of the second board are each formed in two or more rows along the board end part, and each of the side face electrodes is formed on an electrode pad on a closest row to the end part of the respective boards.