# US 5,707,714 A · Printed circuit board for flow soldering

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- Number: US 5,707,714 A
- Document ID: US5707714A
- Status: Granted
- Kind: A
- Application number: 08/712,613
- Filed: 1996-09-13
- Granted: 1998-01-13
- Earliest claimed: 1996-09-13
- Assignees: Mitsuba Corporation
- Inventors: Tetsuya Furutatsu; Yuichi Nagase; Seiji Shioiri
- Web page: https://patentgrep.com/patent/US5707714A

## CPC

- H05K 3/3452: Solder masks
- H05K 3/3468: Application of molten solder, e.g. dip soldering
- H05K 3/3431: {Leadless components}
- H05K 2201/09381: Shape of non-curved single flat metallic pad, land or exposed part thereof; Shape of electrode of leadless component
- H05K 2201/0989: Coating free areas, e.g. areas other than pads or lands free of solder resist
- H05K 2201/099: Coating over pads, e.g. solder resist partly over pads
- H05K 2201/10166: Transistor
- H05K 2201/10636: Leadless chip, e.g. chip capacitor or resistor
- H05K 2203/1178: Means for venting or for letting gases escape
- H05K 2203/1581: Treating the backside of the PCB, e.g. for heating during soldering or providing a liquid coating on the backside
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- Y10S 428/901: Printed circuit
- Y10T 428/24917: including metal layer
- H05K: PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An improved printed circuit board which can reduce or eliminate unsatisfactory soldering caused by trapped gas in surface mounting electronic components by flow soldering is disclosed. According to the invention, the printed circuit board comprises an electrically conductive pattern having a plurality of connection pads to which leads of electronic components are to be connected; and a solder resist layer formed over said electrically conductive pattern and having a plurality of windows which expose said connection pads, wherein at least one of said windows has an extension exposing an additional part of said pad, said extension being substantially narrower than said window. The extension allows the additionally exposed part of the pad to contact with the solder even when the associated pad is almost entirely covered by the trapped gas, so that the solder is pulled to the pad and spread over the pad. Because the extension require a small area, it is effective even when the components are mounted at a high density.

## Claims

### Claim 1

A printed circuit board suitable for surface mounting electronic components by flow soldering, comprising:
an insulating base board;
an electrically conductive pattern formed on said base board, said electrically conductive layer comprising a plurality of connection pads to which leads of said components are to be connected; and
a solder resist layer formed over said electrically conductive pattern, said solder resist layer having a plurality of windows which expose said connection pads,
wherein at least one of said windows has an extension exposing an additional part of an associated connection pad, said extension being substantially narrower than said window.

### Claim 2 (depends on 1)

A printed circuit board according to claim 1, wherein said extension of said window extends away from an adjacent electronic component.

### Claim 3 (depends on 2)

A printed circuit board according to claim 2, wherein said extension of said window extends in an upstream direction with respect to a flow direction of solder relative to said printed circuit board.

### Claim 4 (depends on 2)

A printed circuit board according to claim 2, wherein said extension of said window extends in a downstream direction with respect to a flow direction of solder relative to said printed circuit board.