GB2258183A - Solder mask defined printed circuit board - Google Patents

Solder mask defined printed circuit board Download PDF

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Publication number
GB2258183A
GB2258183A GB9216263A GB9216263A GB2258183A GB 2258183 A GB2258183 A GB 2258183A GB 9216263 A GB9216263 A GB 9216263A GB 9216263 A GB9216263 A GB 9216263A GB 2258183 A GB2258183 A GB 2258183A
Authority
GB
Grant status
Application
Patent type
Prior art keywords
solder
mask
board
pad
pads
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9216263A
Other versions
GB9216263D0 (en )
Inventor
Carl N Garcia
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions Inc
Original Assignee
Motorola Solutions Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00Apparatus or processes for manufacturing printed circuits
    • H05K3/30Assembling printed circuits with electric components, e.g. with resistor
    • H05K3/32Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
    • H05K3/34Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
    • H05K3/3452Solder masks
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00Printed circuits
    • H05K1/02Details
    • H05K1/0266Marks, test patterns, inspection means or identification means
    • H05K1/0269Marks, test patterns, inspection means or identification means for visual or optical inspection
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09209Shape and layout details of conductors
    • H05K2201/09654Shape and layout details of conductors covering at least two types of conductors provided for in H05K2201/09218 - H05K2201/095
    • H05K2201/09781Dummy conductors, i.e. not used for normal transport of current; Dummy electrodes of components
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09818Other shape and layout details not provided for in H05K2201/09009 - H05K2201/09209; Shape and layout details covering several of these groups
    • H05K2201/099Coating over pads, e.g. solder resist partly over pads
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05KPRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/09Shape and layout
    • H05K2201/09818Other shape and layout details not provided for in H05K2201/09009 - H05K2201/09209; Shape and layout details covering several of these groups
    • H05K2201/09918Optically detected marks used for aligning tool relative to the PCB, e.g. for mounting of components

Abstract

The printed circuit board comprises a dielectric material (403) having a plurality of solder pads (401). A solder mask (405) is photographically defined on the dielectric material (403) and the plurality of solder pads (401) such that the solder mask (405) overlaps the edges of the solder pads (401) and fiducials. The solder mask (405) thus defines the solder pads (401), providing a more uniform size and shape for the pads (401). <IMAGE>

Description

SOLDER MASK DEFINED PRINTED CIRCUIT BOARD Field of the Invention The present invention relates generally to the field of printed circuit board manufacturing.

Background of the Invention A solder mask on a printed circuit board prevents solder from connecting traces to pads that should not be connected.

The mask can be applied by screening the material on the board, leaving solder pads free from the mask for a later soldering operation.

In applying the mask to the board, a border is left around the solder pads where there is neither solder mask nor solder pad. This accommodates any inaccuracies in applying the solder mask by allowing for a shifting of the solder mask.

Without the border, if the mask was shifted in one direction too far, the mask would cover too much of the solder pad. The border allows the mask to be shifted and still enable all of the solder pad to be exposed. This concept is illustrated in FIGs.

1A and B. FIG. 1A shows the ideal situation of a solder mask (a) applied without error, leaving a border (c) between the solder pad (b) and mask (a). FIG. 1B shows the typical situation where the mask has shifted, exposing portions of other solderable surfaces attached to the solder pads. An electronic part (d), shown in dotted lines, may now shift due to the irregular shaped pad. This can cause two parts to short together or a part may lift up on one end during the soldering process due to non-uniform surface tension.

FIG. 2 illustrates another prior art example of a solder mask applied on a printed circuit board. This board has an optical fiducial that is known in the art to be used as a reference point in the placement of the solder pads during the circuit board fabrication.

Another problem of typical solder mask application is illustrated in FIG. 3; the application of solder paste is more difficult. FIG. 3 shows a cross section of a printed circuit board where there is a gap between the solder pad (e) and the solder mask (f). When the solder paste stencil (g) is placed over the printed circuit board, it will be higher on the side resting with the mask over the trace (i) and there will be an air gap (h) on the sides with no trace. This allows the solder paste to flow through this air gap, creating non-uniform solder paste application and unwanted paste residue on the bottom surface of the stencil. This is caused by the non-planar surface surrounding the pad, preventing a good gasket seal between the bottom of the stencil and the board.Solder paste can also flow onto the trace (i) attached to the pad, where there should have been solder mask material and onto the exposed dielectric (j) on three sides of the pad. There is a resulting need for more uniform solder mask application.

Summary of the Invention This invention addresses at least some of the deficiencies which prevail in the prior art described above. In accordance with the present invention there is provided a circuit board which comprises a dielectric material with a plurality of solderable areas thereon. A solder mask material is disposed on the dielectric material and the plurality of solderable areas such that substantially no dielectric material is exposed between the solderable areas and the solder mask material.

An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings.

Brief Description of the Drawings FIGs. 1A and B show a top view of the prior art application of a solder mask.

FIG. 2 shows a top view of the prior art application of a solder mask on a printed circuit board having a fiducial.

FIG. 3 shows a cross section of the prior art application of a solder mask.

FIG. 4 shows a cross section view of a preferred embodiment of a solder mask used to define solder pads in accordance with the present invention.

FIG. 5 shows a top view of solder mask of Fig. 4 used to define solder pads and fiducials in accordance with the present invention.

Detailed Description of the Preferred Embodiment FIG. 5 illustrates a printed circuit board arrangement comprising a printed circuit board and a preferred embodiment of a solder mask used to define solder pads and fiducials thereon. The preferred embodiment of the solder mask overlaps the areas of the printed circuit board designated for the solder pads and fiducials. Moreover, the use of the preferred embodiment of the solder mask results in the formation of more uniformly sized solder pads.

FIG. 5 shows typical solder pads 301-303 for a gull wing lead shape integrated circuit package. One of the solder pads 302 is connected to a trace 304 while another is connected to a plated through hole 305. These items, as well as the outline shown around the pads 306-308 and fiducial 320, is shown in dotted lines as they are the part of the copper covered by the solder mask 310.

The solder pads 301-303 and fiducial 312 fabricated using the preferred embodiment of the solder mask are slightly larger than typical, prior art solder pads. The increase in size is substantially equal to the border of the prior art. This enables the solder mask 310 to overlap 311 the solder pad 303 and fiducial 312 while maintaining the same surface area of the solder pad and fiducial as in the prior art. The increase in the size of the solder pad and fiducial does not reduce the useable real estate on the board since the size increase is equal to the unusable border between the pad or fiducial and the solder mask of the prior art.

Plated through holes can actually be placed closer to the pads using the solder mask of the present invention since there is no danger of the mask not covering the hole. This is also true of traces placed between the solder pads. Since there is no longer a border between the solder mask and the solder pad, the traces can be placed closer to the pad without danger of the mask missing the trace, thereby allowing solder to mistakenly connect the pad to the trace.

Another benefit of the present invention is illustrated in FIG. 4. This drawing shows a cross section of a solder pad 401 connected to a trace 402 on the printed circuit board dielectric 403. It can be seen that the solder mask 404 overlaps 405 the pad on all sides. The mask 404 also completely covers the trace 402 connected to the pad 401. The mask 404 now forms a coplanar, level surface for the solder paste stencil 410 to rest on, forming a gasket between the board and the stencil 410. This prevents the solder paste from flowing to unwanted parts of the board.

It can be seen from both FIGs. 4 and 5 that the solder mask now completely encapsulates the solder pad. This provides the benefit of holding the pad down while an electronic component soldered to the pad is removed or a solder joint is repaired.

The solder mask defined pads and fiducials also provide a very precise geometry. Since the solder mask application is one of the last processes in board fabricating, it can be used to cover up dimensional changes in the board from all prior processes. By defining the pads and fiducials by the solder mask, all prior board fabrication process dimensional changes are eliminated. The soldermask defined pads and fiducials thus provide a precisely defined board for subsequent board assembly processes (solder paste print, part placement, etc.).

While the solder mask of the present invention can be applied using a screening method, the preferred embodiment uses a photo-defining method. This results in cleaner lines between the mask and the pad.

Claims (5)

Claims
1. A printed circuit board having a plurality of solder mask-defined solderable areas,the board comprising: a dielectric material with the plurality of solderable areas coupled thereon; and solder mask material disposed on the dielectric material and the plurality of solderable areas such that substantially no dielectric material is exposed between the solderable areas, and the solder mask material.
2. The printed circuit board of claim 1 wherein the plurality of solderable areas include solder pads, plated through holes, fiducials and traces.
3. A printed circuit board having at least one soldermask-defined solder pad, the board comprising: a dielectric material with at least one of solder pad coupled thereon; and solder mask material disposed on the dielectric material and at least one solder pad such that the solder mask material substantially covers the edges of the solder pad.
4. A printed circuit board in accordance with claim 1, or 3, wherein the solder-mask material is deposited on the dielectric material by a photo-defining method.
5. A printed circuit board substantially as described herein with reference to Figs. 4 and 5 of the accompanying drawings.
GB9216263A 1991-08-01 1992-07-30 Solder mask defined printed circuit board Withdrawn GB9216263D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US73897991 true 1991-08-01 1991-08-01

Publications (2)

Publication Number Publication Date
GB9216263D0 GB9216263D0 (en) 1992-09-09
GB2258183A true true GB2258183A (en) 1993-02-03

Family

ID=24970298

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9216263A Withdrawn GB9216263D0 (en) 1991-08-01 1992-07-30 Solder mask defined printed circuit board

Country Status (1)

Country Link
GB (1) GB9216263D0 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0696159A1 (en) * 1994-08-03 1996-02-07 International Business Machines Corporation Printed wiring board
EP0723387A1 (en) * 1995-01-19 1996-07-24 Digital Equipment Corporation Soldermask gasketing of printed wiring board surface mount pads
EP0952762A1 (en) * 1996-12-19 1999-10-27 Ibiden Co, Ltd. Printed wiring board and method for manufacturing the same
WO2002078411A1 (en) * 2001-03-22 2002-10-03 Siemens Aktiengesellschaft Circuit support element for electronic devices, in particular for communication terminals

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB851476A (en) * 1956-04-13 1960-10-19 Emi Ltd Improvements in or relating to the soldering of conductors supported on panels
US4767892A (en) * 1986-05-16 1988-08-30 Alpine Electronics Inc. Printed-wiring board
EP0285701A1 (en) * 1987-04-08 1988-10-12 Nippon CMK Corp. Printed wiring board

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB851476A (en) * 1956-04-13 1960-10-19 Emi Ltd Improvements in or relating to the soldering of conductors supported on panels
US4767892A (en) * 1986-05-16 1988-08-30 Alpine Electronics Inc. Printed-wiring board
EP0285701A1 (en) * 1987-04-08 1988-10-12 Nippon CMK Corp. Printed wiring board

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0696159A1 (en) * 1994-08-03 1996-02-07 International Business Machines Corporation Printed wiring board
US5815919A (en) * 1994-08-03 1998-10-06 International Business Machines Corporation Process for producing an interconnect structure on a printed-wiring board
EP0723387A1 (en) * 1995-01-19 1996-07-24 Digital Equipment Corporation Soldermask gasketing of printed wiring board surface mount pads
US7385146B2 (en) 1996-12-19 2008-06-10 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
US7712212B2 (en) 1996-12-19 2010-05-11 Ibiden Co., Ltd. Method for manufacturing printed wiring board
EP0952762A4 (en) * 1996-12-19 2005-08-31 Ibiden Co Ltd Printed wiring board and method for manufacturing the same
US7361849B2 (en) 1996-12-19 2008-04-22 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
US7371976B2 (en) 1996-12-19 2008-05-13 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
EP0952762A1 (en) * 1996-12-19 1999-10-27 Ibiden Co, Ltd. Printed wiring board and method for manufacturing the same
US7388159B2 (en) 1996-12-19 2008-06-17 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
US7449791B2 (en) 1996-12-19 2008-11-11 Ibiden Co., Ltd. Printed circuit boards and method of producing the same
EP1921902A3 (en) * 1996-12-19 2009-03-25 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
US7585541B2 (en) 1996-12-19 2009-09-08 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
US7615162B2 (en) 1996-12-19 2009-11-10 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
USRE43509E1 (en) 1996-12-19 2012-07-17 Ibiden Co., Ltd. Printed wiring board and method for manufacturing the same
WO2002078411A1 (en) * 2001-03-22 2002-10-03 Siemens Aktiengesellschaft Circuit support element for electronic devices, in particular for communication terminals

Also Published As

Publication number Publication date Type
GB9216263D0 (en) 1992-09-09 grant

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WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)