CA2073809A1 - Solder maks defined printed circuit board - Google Patents
Solder maks defined printed circuit boardInfo
- Publication number
- CA2073809A1 CA2073809A1 CA 2073809 CA2073809A CA2073809A1 CA 2073809 A1 CA2073809 A1 CA 2073809A1 CA 2073809 CA2073809 CA 2073809 CA 2073809 A CA2073809 A CA 2073809A CA 2073809 A1 CA2073809 A1 CA 2073809A1
- Authority
- CA
- Canada
- Prior art keywords
- solder
- pads
- circuit board
- mask
- printed circuit
- 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.)
- Abandoned
Links
- 229910000679 solder Inorganic materials 0.000 title claims abstract description 85
- 239000003989 dielectric material Substances 0.000 claims abstract description 10
- 239000000463 material Substances 0.000 claims description 10
- 230000000873 masking effect Effects 0.000 claims description 2
- 238000000034 method Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- 238000012216 screening Methods 0.000 description 2
- 238000005476 soldering Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 241000272168 Laridae Species 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 239000002305 electric material Substances 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
Landscapes
- Electric Connection Of Electric Components To Printed Circuits (AREA)
Abstract
SOLDER MASK DEFINED PRINTED CIRCUIT BOARD
Abstract of the Disclosure The printed circuit board of the present invention is comprised of a dielectric material (403) having a plurality of solder pads (401). A solder mask (405) is photographically de-fined on the dielectric material (403) and the plurality of solder pads (401) such that the solder mask (405) overlaps the edges (405) 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.
Abstract of the Disclosure The printed circuit board of the present invention is comprised of a dielectric material (403) having a plurality of solder pads (401). A solder mask (405) is photographically de-fined on the dielectric material (403) and the plurality of solder pads (401) such that the solder mask (405) overlaps the edges (405) 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.
Description
SOL~ER MASK DEFINED PRINlrED ClRCUIT BOAE~D
~Yeldof~be Im~ion S The present invention relates generally to the field of printed circuit board manufacturing.
Ba~kgroundof~be h~ tion 1 0 A solder mask on a printed circuit board prevents sol-der from connecting traces to pads that ~hould not be con-nected. The mask can be applied by screening the material on the board, leaving solder pads free from the mask for a later soldering operation.
1 ~ In applying the mask to the board, a border is left around the solder pads where there is neither ~older mask nor solder pad. This accommodates any inaccuracies in ap-plying the solder mask by allowing for a shifting of the ~older masl~. Without the border, if the mask was shifted in one di-2 0 rection too far, the mask would cover too much of the solder pad. The border allows the ma~k to be shifted and still enable all of the solder pad to be exposed. This concept is illustrated in FIGs. lA and B. FIG. lA shows the ideal situation of a 801-der mask (a) applied without error, leaving a border (c) be-2 5 tween the solder pad (b) and mask (a). FIG. lB shows the typ-ical 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 3 0 together or a part may lift up on one end during the soldering proces~ 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 refer-3 ~ ence point in the placement of the ~older pads during the circuit board fabrication.
-2- 2V7~9 Another problem of typical solder mask application i~
lustrated in FIG. 3; the application of solder paste is more dif-ficult. FIG. 3 shows a cross section of a pnnted circuit board where there is a gap between the solder pad (e) and the solder ma~k (f). When the solder paste ~tencil (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. Thi~ allows the solder paste to flow through this air gap, creating non-uniform solder paste ap-plication and unwanted p~ste re~idue on the bottom ~urface of the ~tenMl. This i8 caused by the non-planar surface sur-rounding the pad, preventing a good gasket seal between the bottom of the stencil and the boart. Solder paste can also flow onto the trace (i) attached to t~e pad, where there should have been solder mask material and onto the exposed dielectric (j) on three sides of the pad. There is a restllting need for more uniform solder mask application.
9umm~y of 1 he Illventio l~e printed circuit board of the present invention is comprised of a dielectric material with a plurality of solder-able areas thereon that are located by fiducials. A solder masking material is disposed on the dielectric material and 2 5 the plurality of solderable areas such that substantially no di-electric material is exposed between the solderable areas and the solder mask material.
B~eDes~ip1;ion of the l~rawing~
FIGs. lA and B show a top view of the prior art applica-tion 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.
3 5 FIG. 3 shows a cross section of the prior art application of a solder mask.
2~7~8~9 FIG. 4 shows a cro~s section view of the solder mssk de-fined solder pads in accordance with the present invention.
FIG. 5 shows a top view of solder mask defined so1der pads and fiducials in accordance with the present invention.
Detailed Des~iption of tb~ P~md Embodim~t The printed circuit board of the present invention, illus-trated in FIG. 5, provides solder mask defined solder pads and fiducials, resulting in a more uniform size solder pad. A
~ovel concept of the printed circuit board is to overlap the sol-der mask over the edges of the aolder pads and fiducials.
FIG. 5 shows typical solder pads (301 - 303) for a gull wing lead shape integrated circuit package. One of the solder l 5 padB (302) is connected to a trace (304) while another iB con-nected 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).
2 0 The ~older pads (301 - 303) and fiducial (312) of the pre-sent invention are slightly larger than typical 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 2 5 same surface area of the solder pad and fiducial as in the prior art. The increase in the size of the solder pad and fidu-cial 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.
3 0 Plated through holes can actually be placed closer to the pads using the solder mask of the present invention since there i8 no danger of the mask not covering the hole. Thi8 is also true of traces placed between the solder pads. Since there is no longer a border between the solder mask and the solder 3 ~ pad, the traces can be placed cJoser to the pad without danger 4 2073~9 of the mask missing the trace, thereby allowing solder to mis-takenly connect the pad to the trace.
Another benefit of the present invention ia illustrated in FIG. 4. ThiB drawing shows a cross section of a solder pad (401) connected to a trace (402) on the printed circuit board di-electric (403). It can be seen that the solder mask (404) over-laps (405) the pad on all sides. The mask (404) also completely covers tha trace (402) connected to the pad (401). The mask (404) now forms a coplanar, level surface for the solder paste 1 0 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 encapsulate~ the solder pad. This pro-1 5 vides the benefit of holding the pad down while an electronic component soldered to the pad i~ 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 2 0 one of the last procesaes in board fabricating, it can be used to cover up dimensional changes in the board from all prior pro-cesses. 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 2 5 provide a precisely defined board for subsequent board assem-bly processes (solder paRte 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 3 0 between the mask and the pad.
~Yeldof~be Im~ion S The present invention relates generally to the field of printed circuit board manufacturing.
Ba~kgroundof~be h~ tion 1 0 A solder mask on a printed circuit board prevents sol-der from connecting traces to pads that ~hould not be con-nected. The mask can be applied by screening the material on the board, leaving solder pads free from the mask for a later soldering operation.
1 ~ In applying the mask to the board, a border is left around the solder pads where there is neither ~older mask nor solder pad. This accommodates any inaccuracies in ap-plying the solder mask by allowing for a shifting of the ~older masl~. Without the border, if the mask was shifted in one di-2 0 rection too far, the mask would cover too much of the solder pad. The border allows the ma~k to be shifted and still enable all of the solder pad to be exposed. This concept is illustrated in FIGs. lA and B. FIG. lA shows the ideal situation of a 801-der mask (a) applied without error, leaving a border (c) be-2 5 tween the solder pad (b) and mask (a). FIG. lB shows the typ-ical 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 3 0 together or a part may lift up on one end during the soldering proces~ 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 refer-3 ~ ence point in the placement of the ~older pads during the circuit board fabrication.
-2- 2V7~9 Another problem of typical solder mask application i~
lustrated in FIG. 3; the application of solder paste is more dif-ficult. FIG. 3 shows a cross section of a pnnted circuit board where there is a gap between the solder pad (e) and the solder ma~k (f). When the solder paste ~tencil (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. Thi~ allows the solder paste to flow through this air gap, creating non-uniform solder paste ap-plication and unwanted p~ste re~idue on the bottom ~urface of the ~tenMl. This i8 caused by the non-planar surface sur-rounding the pad, preventing a good gasket seal between the bottom of the stencil and the boart. Solder paste can also flow onto the trace (i) attached to t~e pad, where there should have been solder mask material and onto the exposed dielectric (j) on three sides of the pad. There is a restllting need for more uniform solder mask application.
9umm~y of 1 he Illventio l~e printed circuit board of the present invention is comprised of a dielectric material with a plurality of solder-able areas thereon that are located by fiducials. A solder masking material is disposed on the dielectric material and 2 5 the plurality of solderable areas such that substantially no di-electric material is exposed between the solderable areas and the solder mask material.
B~eDes~ip1;ion of the l~rawing~
FIGs. lA and B show a top view of the prior art applica-tion 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.
3 5 FIG. 3 shows a cross section of the prior art application of a solder mask.
2~7~8~9 FIG. 4 shows a cro~s section view of the solder mssk de-fined solder pads in accordance with the present invention.
FIG. 5 shows a top view of solder mask defined so1der pads and fiducials in accordance with the present invention.
Detailed Des~iption of tb~ P~md Embodim~t The printed circuit board of the present invention, illus-trated in FIG. 5, provides solder mask defined solder pads and fiducials, resulting in a more uniform size solder pad. A
~ovel concept of the printed circuit board is to overlap the sol-der mask over the edges of the aolder pads and fiducials.
FIG. 5 shows typical solder pads (301 - 303) for a gull wing lead shape integrated circuit package. One of the solder l 5 padB (302) is connected to a trace (304) while another iB con-nected 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).
2 0 The ~older pads (301 - 303) and fiducial (312) of the pre-sent invention are slightly larger than typical 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 2 5 same surface area of the solder pad and fiducial as in the prior art. The increase in the size of the solder pad and fidu-cial 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.
3 0 Plated through holes can actually be placed closer to the pads using the solder mask of the present invention since there i8 no danger of the mask not covering the hole. Thi8 is also true of traces placed between the solder pads. Since there is no longer a border between the solder mask and the solder 3 ~ pad, the traces can be placed cJoser to the pad without danger 4 2073~9 of the mask missing the trace, thereby allowing solder to mis-takenly connect the pad to the trace.
Another benefit of the present invention ia illustrated in FIG. 4. ThiB drawing shows a cross section of a solder pad (401) connected to a trace (402) on the printed circuit board di-electric (403). It can be seen that the solder mask (404) over-laps (405) the pad on all sides. The mask (404) also completely covers tha trace (402) connected to the pad (401). The mask (404) now forms a coplanar, level surface for the solder paste 1 0 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 encapsulate~ the solder pad. This pro-1 5 vides the benefit of holding the pad down while an electronic component soldered to the pad i~ 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 2 0 one of the last procesaes in board fabricating, it can be used to cover up dimensional changes in the board from all prior pro-cesses. 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 2 5 provide a precisely defined board for subsequent board assem-bly processes (solder paRte 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 3 0 between the mask and the pad.
Claims (4)
1. A printed circuit board having a plurality of solder mask defined solderable areas and fiducials,the board comprising:
a dielectric material with the plurality of solderable ar-eas coupled thereon; and solder masking material disposed on the dielectric ma-terial and the plurality of solderable areas such that substan-tially no dielectric material is exposed between the solderable areas, the fiducials, and the solder mask material.
a dielectric material with the plurality of solderable ar-eas coupled thereon; and solder masking material disposed on the dielectric ma-terial and the plurality of solderable areas such that substan-tially no dielectric material is exposed between the solderable areas, the fiducials, 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 and traces.
3. A printed circuit board having a plurality of solder mask defined solder pads, the board comprising:
a dielectric material with the plurality of solder pads coupled thereon; and solder mask material disposed on the dielectric mate-rial and the plurality of solder pads such that the solder mask material substantially covers the edges of the solder pads.
a dielectric material with the plurality of solder pads coupled thereon; and solder mask material disposed on the dielectric mate-rial and the plurality of solder pads such that the solder mask material substantially covers the edges of the solder pads.
4. A printed circuit board having a plurality of solder mask defined solder pads, the board comprising:
a dielectric material with the plurality of solder pads coupled thereon; and solder mask material photo-defined on the dielectric material and the plurality of solder pads such that the solder mask material substantially covers the edges of the solder pads.
a dielectric material with the plurality of solder pads coupled thereon; and solder mask material photo-defined on the dielectric material and the plurality of solder pads such that the solder mask material substantially covers the edges of the solder pads.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US73897391A | 1991-08-01 | 1991-08-01 | |
| US738,973 | 1991-08-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2073809A1 true CA2073809A1 (en) | 1993-02-02 |
Family
ID=24970276
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2073809 Abandoned CA2073809A1 (en) | 1991-08-01 | 1992-07-14 | Solder maks defined printed circuit board |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2073809A1 (en) |
-
1992
- 1992-07-14 CA CA 2073809 patent/CA2073809A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |