NL8002616A - SCREEN PRINTING DEVICE FOR APPLYING ADHESIVE TO A PRINTED WIRING PLATE. - Google Patents

Description

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Br / lli / 1124

Screen printing device for applying adhesive to a printed circuit board.

The invention relates to an apparatus for applying adhesive to a surface and in particular an apparatus for applying adhesive in a specific pattern to a printed circuit board.

The latter can serve, for example, for temporarily attaching chip-shaped parts to the plate.

Printed circuit boards are used for mounting parts to be included in a desired circuit. Such parts are commonly used. temporarily attached to holes or pins of the plate with their connecting wires, after which they are permanently attached to the plate by soldering.

To increase the density of the parts and to reduce the dimensions of the plate, 15 chip-shaped parts are used. These "chips" are generally cylindrical objects with cap-shaped contact pads at both ends instead of lead wires. Therefore, these chips cannot be temporarily attached to the printed circuit board in the normal manner by connecting wires.

For temporarily attaching chip-shaped parts to a printed circuit board, an adhesive resin can be used. This adhesive is applied to the plate in a predetermined pattern corresponding to the places where the chip-shaped parts are to be attached. The chips are then adhered to the plate by the adhesive, their contact pads aligned with metal conductors pre-printed on the plate. The plate with attached parts is then subjected to a normal soldering operation, the chips being soldered to the plate for their permanent mechanical and electrical connection.

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The application of the adhesive in a predetermined pattern is preferably effected by a screen printing operation, in which a wire mesh stretched in a window. silk, organdy or polyester, which is covered in such a way that a pattern of permeable zones is created, is placed directly opposite the printed circuit board. The adhesive is then pushed through the mesh passage zones and transferred onto the surface of the plate in the desired pattern. Then the sieve window. of the. printed 10 plate swings away. However, when the screen frame is pivoted away, there is a drawback that the adhesive threads are pulled and continue to stretch until they break and drop onto the printed circuit board next to the desired adhesive spots. Portions of the plate which are not intended to receive adhesive, such as the conductive cartridges, can thus be covered by dropped adhesive threads. When parts of the conductive patterns intended for soldering to the contact pads of the chips become covered with adhesive wires in this manner, a good solder joint cannot be obtained. The thicker the adhesive layer on the plate, the more difficulties encountered by the appearance of adhesive threads outside the desired adhesive zones.

The invention now aims to provide an apparatus and a method for applying adhesive in a predetermined pattern to a printed circuit board, such that the adhesive is limited to the predetermined pattern and that an adhesive deposit on parts beyond that is avoided.

The invention primarily provides a screen printing apparatus for applying an adhesive in a desired pattern to a surface fixed in a predetermined position, said apparatus arranging a screen having passage zones in the desired pattern, means for parallel positioning from the surface sieve and means for pushing adhesive through the passage zones to the surface, and which is characterized by means that the sieve is operated for a predetermined time 8002616 * -3- keep the adhesive pressed through at a distance parallel to said surface.

The invention further provides a method for applying adhesive in a desired pattern on a substantially flat surface using a sieve stretched in a window with pass zones arranged according to the desired pattern, the method comprising the steps of: stretching the adhesive across the screen in order to press the adhesive into the pass zones, holding the screen parallel to and at a predetermined distance from the surface, pressing the screen with a doctor blade with sufficient force to bend the screen into when it comes into contact with the surface, moving the squeegee over the sieve so that the adhesive is adhered to the surface passage zones, removing the squeegee so that the sieve is its unbent position parallel to and at a predetermined distance from can occupy the surface, and which method is characterized in that the sieve is still parallel to 20 and at a predetermined distance from the surface t held until the adhesive threads bridging the space between the screen and the surface are broken and fall back onto the corresponding areas on the surface.

The invention is further illustrated by the drawings, which show by way of example an embodiment of the device according to the invention, as well as the operation thereof.

Figure 1 shows an embodiment of the device according to the invention in side view.

Figures 2 and 3 are cross sections along the lines II-II and III-III of figure 1, on a larger scale.

Figure 4 is a cross section taken on the line IV-IV of Figure 3.

Figures 5-8 and 10-12 show the operation of the device of Figure 1.

Figure 9 corresponds to Figure 12, but for a prior art method.

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The device of figure 1 has a base 1 on a base plate 11 / which base carries a mounting plate 2 on which a plate 3 with printed wiring can be placed. A rectangular window 6 is pivotally supported 5 by. trunnions 5 in support arms 4 on both sides of the base. A crank arm 7 is fixedly fixed to the frame 6, the free end of the crank arm 7 being connected via a tap IQ to the piston rod 9 of a hydraulic cylinder 8.and to a coupling rod 12. The coupling rod 12, 12 and the cylinder 8 is hinged to the base plate 11 with their other ends. This. means that the frame 6 can be pivoted about the trunnions 5 by moving the piston rod 9 of the cylinder 8 back and forth. The parts 7,8,9,12 and 10 can, if desired, also be present on the other side of the window 6 for the purpose of a balanced operation thereof.

According to figure 1-3, a screen 13 is stretched between the window 6. This screen 13 consists of a wire mesh of each. suitable material, but preferably made of polyester-20. fibers, for example from the Tetoron brand. Both sides of the screen 13. are covered with an impermeable resin, except at the area of the passage zones 14, where a liquid or semi-liquid adhesive can be pressed through the screen.

The thickness of the impermeable zones of the screen 13 is approximately equal to the thickness of the adhesive layer that is to be applied to certain zones of the plate 3. Preferably, the thickness of the covered zones is between 400 µm and 50 µm. The adhesive is pressed through the meshes of the pass zones 14 onto the plate 3 by means of a doctor blade, which will be described later.

At the front and rear of the window 6 there are supports 15, which carry a pair of rods 16, which run almost parallel to the sides of the window 6. Skids 17 with bearings 18 (figure 3) can move along these rods 16, which can be effected by hand or by means of drive means (not shown).

On each carriage 17 there is a pair of pneumatic cylinders 19,20, the piston rods of which are attached to shoulders 17a of the carriage 17. The cylinders 19 are connected by a rod 21 (figure 3) which, by means of a set of screws 22, carries a blister, consisting of a wiper blade 24 of resilient S flexible material, which is held by a cross-section U-shaped support rod 23. The wiper blade 24 extends almost the entire width of the screen 13 and preferably consists of a rubber-like material such as polyurethane rubber.

The pneumatic cylinders 2Q are connected to each other by a rod. 21 ', which, by means of a set of screws 22', carries a doctor blade, consisting of a doctor blade 26, which is held by a cross-section U-shaped support rod 25. This squeegee blade also extends almost the entire width of the sieve 13 and preferably consists of a resilient material such as polyurethane rubber.

It will be clear that the squeegee blade 24 can be moved to one of the sieve 13 by operating the pneumatic cylinders 19. and that the squeegee blade 26 can be moved to one of the sieve 13 by operating the cylinders 20.

In the drawing, the piston rods of the cylinder are 19.20. to the slides 17, and the cylinders themselves attached to the 25 rods 21, 21 ". However, it will be clear that an inverted construction is also possible. with the cylinders 19,20 attached to the slides 17, and the piston rods thereof to the rods 21,21.

Both doctor blades 24 and 26 take an inclined position with respect to the normal plane of the sieve 13 (figure 4) in the opposite direction at an angle of 45-60 °. Due to this angle of inclination of the blades 24, 26 and the use of. resilient, polyurethane rubber therefor reduces the risk of damaging the sieve 13 35, thus extending its life.

The operation of the described device is further illustrated by Figure 5-12. First of all, the window 6 is made by means of the cylinder. 8 is pivoted upwards about the trunnions 3 * λ λ η a λ £ -6- into the drawn position of figure 5. By means not shown, an amount of adhesive 27 is applied across the sieve 13, after which the pneumatic cylinders 20 are operated to lower the smear blade 26 at 5 in the direction of the arrow until it comes into contact with the top surface of the second stage 13.

According to Figure 6, the doctor blade 25, 26 is then moved to the left by means of a drive device (not shown) which engages the slides 1.7 or by hand to the left. In addition, the semi-liquid adhesive 27 is spread through the squeegee blade 26 over the screen 13 and the pass zones 14 are filled with adhesive. The cylinders 20 are then operated to lift the squeegee 26 off the screen 13.

The window 6 is then pivoted about the trunnions 5 back into the position of Figure 7, in which the window 6 extends parallel to the horizontal surface of the printed circuit board 3 at a predetermined distance.

Subsequently, the cylinders 19 are operated to move the push-through doctor blade 24 in the arrow direction downwards to the screen 13, applying sufficient force to bend the screen 13 until it comes into contact with the surface of the plate 3. The bent position of the sieve is indicated by a solid line and the original position by a dotted line.

Then the slides 17 are moved to the right with the blister 24 (according to Figures 7 and 8). The adhesive previously passed through the squeegee 26 into the pass zones 14 is now pushed through the sieve and transferred onto the surface of the plate 3, due to the fact that the 3Q sieve 13 is in contact with this plate under the pressure of the squeegee 24. 3 state. Thus, a layer of adhesive 27 is applied to the plate 3 in a pattern corresponding to the pattern of the zones 14 in the screen 13. Any excess adhesive is slid out in front of the doctor blade 24.

After the blister squeegee 24 has moved all the way to the right, as shown in Figure 10, the cylinders 19 are actuated to lift the squeegee 24 off the screen 13. As a result, the sieve 1B. return to its undistorted position, 8002616 f * -7- in which it runs parallel to plate 3 at a distance.

After the formation of the desired adhesive zones on the plate 3 and after the return of the screen 13 to its undeformed state (figure 10), adhesive-5 threads still appear to extend between the individual adhesive zones on the plate 3 and the corresponding pass zones. 14 of the strainer, which located. above it.

In the prior art, the window 6 with the sieve 13 is pivoted immediately after the return of the squeegee 24 to the position shown in figure 10 back to its inactive initial position, see figure 9. By this pivoting of the window 6 with the sieve 13 the adhesive threads 28 are stretched until they break. Due to the stretching and breaking of the adhesive wires 28, the material thereof can fall on undesired zones of the plate 3, thereby making solder joints impossible. This problem is especially serious in the passage zones 14 which are close to the trunnions 5 and therefore close to the pivot point, because the stretched adhesive threads 28 there have a greater angle of inclination with it. surface of the plate 3.

To solve the problem, the window 6 with the screen 13 is kept in the position of figure 10 for some time. This time is so long (usually 2-6 seconds after the squeegee 24 returns to the drawn position) that the adhesive threads 28 break under the influence of their fluidity and surface tension (see Figure 11). Since the adhesive threads 28 are in this If they extend almost vertically, they have no tendency to fall at undesired locations of the printed circuit board 3 at breakage. After the adhesive threads 28 are broken and dropped, the top of the adhesive zones are automatically flattened by the surface tension.

After the adhesive threads 28 have been broken in the manner described, the frame 6 is pivoted back with the sieve 13 around the trunnions 5 to the initial position (figure 12).

The plate 3 with the predetermined pattern of adhesive zones thereon can then be removed and replaced with another printed circuit board 3. Then, the smear blade 26 can be brought back into contact with the screen 13 to spread adhesive on the screen 13 (Figures 5 and 6) in preparation for the next cycle.

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Claims (8)

A screen printing device for applying an adhesive in a desired pattern on a substantially horizontal surface fixed in a predetermined position, comprising: 5. a screen having transmission zones arranged according to the desired pattern, - means with which the screen is parallel can be arranged on said surface lacquer, and - means by which the adhesive is pressed through the pass zones of the screen and. can be transferred to the surface, characterized in that means are also provided which remotely position the screen (131) for a predetermined time after actuation of the means (23, 241 for pushing the adhesive through the screen parallel to said surface. Device according to claim 1, characterized in that the means for arranging the sieve comprise a frame (6) between which the sieve (131 extends), as well as trunnions (4,51 and means (7t12) for pivoting from the window to the trunnions. Device according to claim 1, characterized in that the means for the. pushing the adhesive through the screen comprises a doctor blade (24) making an acute angle to the screen. Device according to claim 3, characterized in that the doctor blade (24) is made of rubber. 5. Device according to claim 1, characterized in that the means for pushing the adhesive through the sieve comprise a squeegee (25, 26) operative to spread the adhesive over the sieve, and another squeegee (23, 24) that can be moved over the screen to push the adhesive out of the pass zones. Device according to claim 5, 35, characterized in that the doctor blade (261) of the doctor blade squeegee is rubber. & 7. Device for applying an adhesive 8002616-10 in a desired pattern on a substantially horizontal flat surface, comprising: - a screen with passage zones arranged according to the desired pattern, 5. a window between which the screen is tensioned means for pivoting the window between a first and a second position, wherein the sieve in the first position runs at a distance parallel to said surface and in the second position is far from that surface, a smearing doctor with means for bringing this squeegee into contact with the screen and means for moving this squeegee along the screen so that a quantity of adhesive is broken into the pass zones of the screen, a push-through squeegee with means to act as the window in the first position, press this squeegee against the sieve with sufficient force so that part of. the sieve deflects and comes into contact with said surface, and with means for moving the squeegee along the sieve to push dye away from the pass zones and deposit it on said surface, and means for contacting the surface of the blister sieve and the screen while the window remains in the first position, characterized in that means are present which prevent it. keep the window (61 25 in the first position after actuation of the presser squeegee moving means (24) long enough to cause adhesive threads extending between the sieve and the adhesive zones on the surface to break and on these adhesive zones will fall back 8. Method for applying an adhesive in a predetermined pattern on a substantially horizontal flat surface by means of a screen, the pass zones of which are arranged in said pattern, comprising of: - spreading the adhesive over the screen in order to obtain this adhesive to be ironed in the passage zones, - placing the screen at a predetermined distance parallel to said surface, - - pressing a push-through squeegee against the screen with sufficient force to form part of the screen. bend until it comes into contact with the surface, moving the squeegee over the screen so that the adhesive from the pass zones is pressed through and attached to the. underlying areas of the surface are adhered, and - removing the doctor blade so that the sieve can return to its unbent position at a distance parallel to the surface; characterized in that sieve (13) remains in the. spaced 10 parallel to said surface, that adhesive threads (28) extending between the screening zones of the screen and the underlying zones of the surface will break and return to the underlying zones. 8002616