GB2048780A

GB2048780A - Applying patterns of adhesive resin

Info

Publication number: GB2048780A
Application number: GB8014586A
Authority: GB
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1979-05-07
Filing date: 1980-05-02
Publication date: 1980-12-17
Also published as: NL8002616A; FR2456458A1; DE3017492A1; CA1137650A; JPS55148484A

Abstract

A printing screen 13 is angularly displaced to an operative position parallel to, but slightly spaced from a printed circuit board 3 on which an adhesive resin pattern is to be printed. A resilient squeegee blade 24 is wiped across the screen 13 in its operative position for both pressing the screen 13 down against the circuit board 3 and squeezing semi-liquid adhesive resin 27 through the previous printing areas onto the circuit board 3. Upon completion of such wiping operation, the blade 24 is lifted from the screen 13 and the screen 13 is maintained in its operative position parallel to the circuit board 3 for a sufficient time to permit the substantially vertical collapse of adhesive resin threads 28 bridging the space between the printed pattern and the screen 13. There is not therefore any tendency for the resin threads to collapse onto unintended areas. <IMAGE>

Description

SPECIFICATION Applying patterns of adhesive resin This invention relates to apparatuses and methods for applying patterns of adhesive resin to surfaces, more particularly, but not exclusively, to printed circuit boards.

Printed circuit boards are used for mounting components to be included in an electronic circuit.

Such parts are normally temporarily affixed to holes or pins in the circuit board by their wire leads, and a subsequent soldering operation permanently affixes the parts of the circuit board.

Chip-type circuit parts are used to increase the density of the circuit parts and to permit reduction of the size of the circuit board. Chip-type circuit parts are generally cylindrical objects having caplike contacts on their ends rather than wire leads.

Accordingly, chip-type circuit parts cannot be temporarily attached to the circuit board by wire leads in the normal manner prior to soldering.

Adhesive resin may be used for temporarily attaching chip-type parts to a circuit board. The adhesive resin is applied to the circuit board in a predetermined pattern corresponding to the positions where chip-type parts are to be mounted. The chip-type parts are then temporarily attached by the adhesive resin to the circuit board with their contacts aligned with metallic conductors previously printed on the circuit board.

The circuit board with the attached chip-type and other parts is soldered in a conventional soldering operation. In this way, the contacts of the chiptype parts are soldered to the circuit board for permanent mechanical and electrical attachment thereto.

A preferred method of producing the predetermined pattern of adhesive resin includes a silk screening operation in which a fabric screen formed of silk or organdy, but preferably of polyester, and having a pattern of pervious printing areas and impervious non-printing areas formed thereon, is stretched across a supporting frame and is disposed in confronting or face to face relation to the circuit board. The adhesive resin is squeezed through the pervious printing areas onto the surface of the circuit board to duplicate the pattern thereon. The supporting frame is then angularly displaced away from the circuit board. When the supporting frame is thus displaced, resin threads bridging the space between the screen and the circuit board are stretched and laterally inclined until they break and fall on the circuit board adjacent to the desired resin-receiving areas.Portions of the circuit board which are not intended to receive resin, such as the conductive patterns, may be covered by the collapsed resin threads. When portions of the conductive patterns which are provided for solder attachment of the contacts of the chip-type parts become covered with the resin threads, a good solder joint cannot be made. The thicker the layer of adhesive resin deposited on the circuit board, the more difficulty is encountered by coverage with resin threads outside the desired resin-receiving areas.

According to the present invention there is provided apparatus for applying a desired pattern of adhesive resin on a substantially horizontal surface fixed in a predetermined position, the apparatus comprising: a screen having pervious printing areas in said pattern; a frame across which said screen is stretched; means for pivoting said frame between first and second positions; said first position being effective normally to dispose said screen parallel to, and spaced from, said surface; said second position being effective to dispose said screen a greater distance away from said surface; a scraper blade; means for contacting said scraper blade with said screen across a first dimension of said screen; means for translating said scraper blade in contact with said screen across a second dimension of said screen whereby an amount of said adhesive resin is scraped into said pervious printing areas; a squeegee blade; means, effective when said frame is in said first position, for pressing said squeegee blade against said screen across a first dimension of said screen with sufficient force to deflect a portion of said screen contacted by said squeegee blade into contact with said surface; means for translating said squeegee blade in contact with said screen across a second dimension of said screen whereby said adhesive resin in said pervious printing areas is squeezed from the latter and deposited in respective areas on said surface; means for moving said squeegee blade out of contact with said screen while said frame remains in said first position; and means for holding said frame in said first position for a sufficient time after actuation of said means for moving said squeegee blade to permit resin threads bridging between said screen and the deposited areas on said surface to break and fall back into the respective deposited areas.

According to the present invention there is also provided a method of applying'a desired pattern of adhesive resin on a substantially horizontal planar surface using a screen having pervious printing areas arranged in said pattern, the method comprising: scraping said adhesive resin over said screen to scrape said adhesive resin into said pervious printing areas; holding said screen parallel to and spaced a predetermined distance from said surface; pressing a squeegee blade against said screen with sufficient force to deflect a portion of said screen engaged by said blade into contact with said surface; translating said squeegee blade across said screen whereby said adhesive resin in said pervious printing areas is squeezed therefrom and adhered to underlying respective areas of said surface; moving said squeegee blade away from said screen to permit said screen to resume its undeflected condition parallel to and spaced said predetermined distance from said surface; and continuing to hold said screen parallel to and spaced said predetermined distance from said surface until resin threads bridging between said printing areas of said screen and said underlying areas of the surface break and fall back into said underlying areas.

The invention will now be described by way of example with reference to the accompanying drawings, throughout which like reference numerals designate like elements, and in which: Figure 1 is a schematic side elevational view of an embodiment of apparatus for applying adhesive resin to a printed circuit board and according to the invention; Figure 2 is an enlarged cross-sectional view taken along the line Il-Il of Figure 1; Figure 3 is an enlarged cross-sectional view taken along the line Ill-Ill of Figure 1; Figure 4 is a cross-sectional view taken along the line IV-lV of Figure 3; Figures 5 to 8 and 10 to 12 are diagrammatic side views of the apparatus of Figure 1 to which reference will be made in describing the operation thereof; and Figure 9 is a diagrammatic side view similar to that of Figure 12, but to which reference will be made in describing the problem encountered with the prior art.

Referring to Figure 1, it will be seen that an embodiment of apparatus for applying adhesive resin on a printed circuit board includes a base 1 on a supporting plate 11 for carrying a mounting plate 2 on which a printed circuit board 3 may be mounted. A bracket 4 is fixed at each side of the base 1 and supports a respective pivot pin 5. A rectangular frame 6 is pivotally supported, at one end, on the pins 5. A crank arm 7 is fixedly attached to the frame 6, and the lower or free end of the crank arm 7 is connected through a pin 10 to a piston rod 9 of a hydraulic or oil pressure cylinder 8 and to a link 12. The link 12 and the pressure cylinder 8 are hinged at their lower ends to the supporting plate 11. The frame 6 may thus be angularly displaced about the pins 5 by extension and retraction of the piston rod 9 of the pressure cylinder 8.The crank arm 7, the pressure cylinder 8 the piston rod 9, the link 12 and the pin 10 may optionally be duplicated at the opposite side of the framed 6 for balanced actuation thereof.

Referring now also to Figures 2 and 3, the frame 6 is shown to have a screen 13 stretched across it with a predetermined tension. The screen 13 is a fabric mesh of any suitable material, but is preferably a polyester synthetic fibre, such as the material sold under the trademark Tetoron. Both surfaces of the screen 13 are coated with an impervious resin except for pervious printing areas 14 which permit the passage of liquid or semiliquid adhesive through the uncoated meshes thereof. The thickness of the impervious nonprinting areas of the screen 1 3 is approximately equal to the thickness of adhesive resin which it is desired to apply to selected areas of the circuit board 3. In a preferred embodiment, the thickness of the impervious areas is about 400 to about 500 microns.Adhesive resin is squeezed through the meshes of the printing areas 14 of the screen 1 3 onto the circuit board 3 by a squeeze member or squeegee to be described hereinafter.

Supporting members 1 5 (Figure 1), at each side of the front and rear of the frame 6, support a pair of rods 16 substantially parallel to the sides of the frame 6. Slide blocks 17 on slide bearings 18 (Figure 3) are slidable along the rods 16 either manually or by conventional drive means (not shown).

A pair of air cylinders 19 and 20 are provided for each slide block 1 7 and have their piston rods attached to stepped portions 1 7a of the respective slide blocks 17. A bar 21 is connected between the air cylinders 1 9 (Figure 3). A squeegee comprising a U-shaped support bar 23 holding a resiliently flexible wiper or squeegee blade 24, is connected to the bar 21 by adjustable screws 22.

The squeegee blade 24 extends over substantially the entire width of the screen 13 and is preferably of rubber-like material, such as, polyurethane rubber.

A second bar 21' is connected between the air cylinders 20. A scraper comprising a U-shaped support bar 25 holding a scraper blade 26 is attached through adjustable screws 22' to the bar 21'. The scraper blade 26 also extends over substantially the entire width of the screen 1 3 and is also preferably of a resilient material, such as, polyurethane rubber.

As will be evident, actuation of the air cylinders 1 9 is effective to move the squeegee blade 24 towards and away from the screen 13. Similarly, actuation of the air cylinders 20 is effective to move the scraper blade 26 towards and away from the screen 13.

Although the air cylinders 1 9 and 20 are shown with their piston rods attached to the side blocks 17 and their cylinders attached to the bars 21 and 21', respectively, it is apparent that the cylinders of the air cylinders 19 and 20 may alternatively be attached to the side blocks 1 7 while their piston rods are connected to the bars 21 and 21', respectively.

The squeege blade 24 and the scraper blade 26 are inclined relative to the normal and undeflected plane of the screen 13 (Figure 4) in opposite directions at angles of from 450 to 600. Such inclination of the blades 24 and 26 and the use of resilient polyurethane rubber for these parts reduces the incidence of damage to, and increases the life of the screen 13.

Referring now to Figure 5, it will be seen that the frame 6 is initially angularly displaced by the pressure cylinder 8 in the clockwise direction about the pins 5 into the illustrated inclined elevated position. An amount of adhesive resin 27 is applied across the screen 1 3 by any conventional means (not shown) and the air cylinders 20 are actuated to lower the scraper blade 26 towards, or into contact with, the upper surface of the screen 13, as indicated by the arrow.

As shown in Figure 6, the support bar 25 and the scraper blade 26 are moved leftward with the slide blocks 1 7 by a conventional drive apparatus (not shown) or manually, during which time the semi-fluid adhesive resin 27 is scraped across the screen 1 3 by the scraper blade 26. The printing areas 14 are thus filled with the adhesive resin 27, and then the air cylinders 20 are actuated to raise the scraper blade 26 from the screen 13.

The frame 6 is angularly displaced in the counter-clockwise direction about the pins 5 into the position shown in Figure 7, and in which the frame 6 is parallel to but spaced a predetermined distance from the horizontal surface of the circuit board 3.

The air cylinders 1 9 are actuated to force the squeegee blade 24 downward against the screen 13, as shown by the arrow, with sufficient force to deflect the screen 1 3 from its normal plane shown in dot-dash lines in Figure 7 into contact with the surface of the circuit board 3 as shown by the solid line.

The slide blocks 1 7 are now moved rightward (in Figures 7 and 8) drawing the squeegee blade 24 with them. The adhesive resin 27 previously scraped into the printing areas 14 by the scraper blade 26 is now pressed therethrough and adhered to the surface of the circuit board 3 as the squeegee blade 24 presses the screen 1 3 into contact therewith, thus leaving a thickness of the adhesive resin 27 on the circuit board 3 in a pattern corresponding to the pervious printing areas 14 of the screen 13. Any excess adhesive resin 27 is moved along ahead of the squeegee blade 24.

The squeegee blade 24 is moved fully to the right, as shown in Figure 10, and the air cylinders 1 9 are actuated to raise the squeegee blade 24 from the screen 13. This permits the screen 13 to resume its undepressed shape in which it is parallel to, but spaced from the circuit board 3.

Immediately after forming the desired areas of the adhesive resin 27 on the circuit board 3 and the return of the screen 1 3 to its undepressed shape, resin threads 28 (Figure 10) bridge the space between the individual pattern areas of the adhesive resin 27 deposited on the circuit board 3 and the respective printing areas 14 immediately thereabove.

In the prior art, the frame 6 and the screen 13 are angularly displaced to their initial inoperative positions shown in Figure 9 immediately foliowing the return of the squeegee blade 24 to the position shown in Figure 10. Such angular displacement of the frame 6 and the screen 13 stretches the resin threads 28 until the latter break. Due to the elongation and breaking of the resin threads 28, the material thus pulled from the adhesive resin 28 may fall upon unintended areas of the circuit board 3 and make satisfactory solder connections thereto impossible. This problem is especially severe at the printing areas 14 nearer to the pins 5 due to the fact that these areas are relatively closer to the centre of rotation and the elongated resin threads 28 extending therefrom are thus more inclined to the surface of the circuit board 3.

In order to solve the above problem, in the embodiment described, the frame 6 and the screen 13 are maintained in the position of Figure 10 for a long enough period, suitably two to six seconds after the return of the squeegee blade 24 to the position shown in Figure 10, until the fluidity of the resin and its surface tension cause the resin threads 28 to break, as is shown in Figure 11. Since the resin threads 28 extend straight upward or vertically from coated areas of the circuit board 3 until they are broken as described above, there is no tendency for the resin threads 28 to fall over onto unintended areas of the circuit board 3. After the resin threads 28 break and fall to the surface of their respective pattern areas, surface tension smooths the tops of the pattern areas. Once the resin threads 28 have broken, the frame 6 and the screen 13 are angularly displaced in the counter-clockwise direction about the pins 5, as shown in Figure 12.

The circuit board 3 having the predetermined pattern of adhesive resin 27 thereon can then be removed and replaced by a new circuit board 3 to receive the predetermined pattern, and the scraper blade 26 can again be moved into contact with the screen 1 3 to spread the adhesive resin 27 on the screen 13 in preparation for the next cycle.

Claims

1. Apparatus for applying a desired pattern of adhesive resin on a substantially horizontal surface fixed in a predetermined position, the apparatus comprising: a screen having pervious printing areas in said pattern; means for positioning said screen parallel to said surface; means actuable for squeezing said adhesive resin through said printing areas onto said surface; and means for holding said screen parallel to and spaced a predetermined distance from said surface for a predetermined time after actuation of said means for squeezing.

2. Apparatus according to claim 1 wherein said means for positioning the screen includes a frame across which the screen is stretched, pivot means and means for angularly displacing said frame about said pivot means.

3. Apparatus according to claim 1 wherein said means for squeezing includes a squeegee blade inclined at an acute angle to said screen.

4. Apparatus according to claim 3 wherein said squeegee blade is of a resilient material.

5. Apparatus according to claim 1 wherein said means for squeezing includes a scraper blade operative to spread said adhesive resin on said screen whereby said printing areas are filled with said adhesive resin, and a squeegee blade movable over said screen to squeeze the adhesive resin from said printing areas.

6. Apparatus according to claim 5 wherein said scraper means includes a scraping blade of a resilient material.

7. Apparatus for applying a desired pattern of adhesive resin to a substantially horizontal plane surface, the apparatus comprising: a screen having pervious printing areas in said pattern; a frame across which said screen is stretched; means for pivoting said frame between first and second positions; said first position being effective normally to dispose said screen parallel to, and spaced from, said surface; said second position being effective to dispose said screen a greater distance away from said surface; a scraper blade; means for contacting said scraper blade with said screen across a first dimension of said screen; means for translating said scraper blade in contact with said screen across a second dimension of said screen whereby an amount of said adhesive resin is scraped into said pervious printing areas; a squeegee blade; means, effective when said frame is in said first position, for pressing said squeegee blade against said screen across a first dimension of said screen with sufficient force to deflect a portion of said screen contacted by said squeegee blade into contact with said surface; means for translating said squeegee blade in contact with said screen across a second dimension of said screen whereby said adhesive resin in said pervious printing areas is squeezed from the latter and deposited in respective areas on said surface; means for moving said squeegee blade out of contact with said screen while said frame remains in said first position; and means for holding said frame in said first position for a sufficient time after actuation of said means for moving said squeegee blade to permit resin threads bridging between said screen and the deposited areas on said surface to break and fall back into the respective deposited areas.

8. A method of applying a desired pattern of adhesive resin on a substantially horizontal planar surface using a screen having pervious printing areas arranged in said pattern, the method comprising: scraping said adhesive resin over said screen to scrape said adhesive resin into said pervious printing areas; holding said screen parallel to and spaced a predetermined distance from said surface; pressing a squeegee blade against said screen with sufficient force to deflect a portion of said screen engaged by said blade into contact with said surface; translating said squeegee blade across said screen whereby said adhesive resin in said pervious printing areas is squeezed therefrom and adhered to uderlying respective areas of said surface; moving said squeegee blade away from said screen to permit said screen to resume its undeflected condition parallel to and spaced said predetermined distance from said surface; and continuing to hold said screen parallel to and spaced said predetermined distance from said surface until resin threads bridging between said printing areas of said screen and said underlying areas of the surface break and fall back into said underlying areas.

9. Apparatus for applying a desired pattern of adhesive resin on a substantially horizontal surface fixed in a predetermined position, the apparatus being substantially as hereinbefore described with reference to Figures 1 to 8 and 10 to 12 of the accompanying drawings.

10. A method of applying a desired pattern of adhesive resin on a substantially horizontal planar surface using a screen having pervious printing areas arranged in said pattern, the method being substantially as hereinbefore described with reference to Figures 1 to 8 and 10 to 12 of the accompanying drawings.