Conveyorized vacuum applicator and method of applying a dry film resist to a printed circuit board

• US 20030121604A1
• Filed: 12/11/2002
• Published: 07/03/2003
• Est. Priority Date: 08/25/1999
• Status: Active Grant

• Current Assignee: Shipley Company, LLC (Dow, Inc.)
• Original Assignee: Shipley Company, LLC (Dow, Inc.)
• Inventors: Stanich, Roberto, Novello, Osvaldo, Keil, Charles R.
• Granted Patent: US 6,971,429 B2
• Time in Patent Office: Days
• US Class Current: 156/286
• CPC Class Codes: B32B 2309/68 Vacuum
• CPC Class Codes: B32B 2457/08 PCBs, i.e. printed circuit boards
• CPC Class Codes: B32B 37/0007 involving treatment or provisions in order to avoid deformation or air inclusion, e.g. to improve surface quality
• CPC Class Codes: B32B 37/182 one or more of the layers being plastic
• CPC Class Codes: G03F 7/161 using a previously coated surface, e.g. by stamping or by transfer lamination
• CPC Class Codes: H05K 2203/068 Features of the lamination press or of the lamination process, e.g. using special separator sheets
• CPC Class Codes: H05K 2203/085 Using vacuum or low pressure
• CPC Class Codes: H05K 2203/1105 Heating or thermal processing not related to soldering, firing, curing or laminating, e.g. for shaping the substrate or during finish plating
• CPC Class Codes: H05K 3/281 by means of a preformed insulating foil H05K3/284 takes precedence
• CPC Class Codes: Y10S 428/901 Printed circuit
• CPC Class Codes: Y10T 156/17 Surface bonding means and/or assemblymeans with work feeding or handling means
• CPC Class Codes: Y10T 156/1744 Means bringing discrete articles into assembled relationship
• CPC Class Codes: Y10T 156/1768 Means simultaneously conveying plural articles from a single source and serially presenting them to an assembly station

Abstract

An improved method of and apparatus that is continuously automatically operative in an in-line system is described for applying under vacuum, heat and mechanical pressure a dry film photoresist-forming layer to printed circuit boards (200) that already have been prelaminated by the loose application thereto of the dry film resist as discrete cut sheets within the confines of the surface of the boards whereby a laminate without entrapped air bubbles and closely conforming to the raised circuit traces and irregular surface contours of the printed circuit board is obtained. Featured is a conveyorized vacuum applicator (12) comprising two independent vacuum lamination chambers (18,20) in end-to-end relation. The first vacuum chamber operates at ambient temperature to draw off all of the air entrapped between the dry film resist and the surface of the printed circuit board at conditions that do not result in premature tacking of the dry film to the surface of the board. Then, in the second vacuum chamber, the photoresist-forming layer is immediately laminated to the printed circuit board under heat and mechanical pressure. The forgoing reduces or eliminates common lamination defects such as premature resist tacking and the attendant need to repair or rework the printed circuit board.

Claims

1. A method of vacuum laminating a dry film photoresist-forming layer onto a prelaminated printed circuit board or other substrate (200) which prevents premature tacking of the dry film to the board or substrate, comprising:

(a) placing the board or substrate in a first vacuum lamination chamber of a vacuum laminator (12) having two independent vacuum lamination chambers (18,20);

(b) drawing a vacuum in said first chamber (18) at ambient temperature for a time sufficient to evacuate substantially all of the air from between the dry film and the surface of the board or substrate and place the dry film in intimate contact with the surface of the board or substrate;

(c) placing the board or substrate in a second vacuum lamination chamber (20) of the vacuum laminator, said second chamber being independent of said first chamber; and

,

(d) applying sufficient heat to the dry film on the board or substrate in said second chamber (20) to cause the dry film to adequately flow and then sufficient mechanical pressure on the board or substrate to thereby force the heated laminate to conform closely to the surface contours of the board or substrate.

2. A method according to claim 1 wherein steps (a)-(d) are operated in-line.

3. A method according to claim 2 wherein steps (a)-(d) are operated in a continuous automated fashion.

4. A method according to claim 3 wherein steps (b) and (d) are operated in alternating sequence to allow at least one prelaminated board or substrate to be in each vacuum chamber at the same time.

5. A method according to claim 3 comprising in an automatic sequential operation:

(a) placing a first board or substrate (200a) on the entrance end of a first moving belt conveyor (22) for movement into the first vacuum lamination chamber (18), the first chamber being defined by an upper platen (150) and a lower platen (146) adapted to be moved into sealing engagement, the first belt conveyor having an endless belt (70) under tension that has an aperture (74) therein and is characterized by having an initial or set-point position such that, as the board or substrate is moved on the endless belt into the region of the first vacuum chamber between the upper and lower platens, the aperture is moved into alignment with and between the board and the lower platen;

(b) sensing the positioning of the board in the first vacuum chamber (18) of the vacuum laminator and stopping the movement of the first belt conveyor (22);

(c) relieving the tension on the endless belt (70) of the first belt conveyor;

(d) lifting the lower platen (146) up through the aperture (74) in the endless belt into sealing engagement with the upper platen (150) and thereby capturing within the first vacuum chamber (18) the board or substrate (200) and at least the portion of the endless belt upon which the board or substrate is positioned;

(e) evacuating the first vacuum chamber (18) at ambient temperature for a time sufficient to draw off all of the air between the loosely applied prelaminated dry film and the surface of the board or substrate, thereby to place the dry film in intimate contact with the board or substrate surface;

(f) when the aforesaid evacuation is complete, allowing atmospheric air to enter the first vacuum chamber (18);

(g) lowering the lower platen (146) down through the aperture (74) in the endless belt (70);

(h) restoring the tension in the endless belt (70) for movement of the evacuated board or substrate out of the first vacuum chamber (18);

(i) conveying the board or substrate (200a) out of the first vacuum chamber (18) and to the entrance end of a second moving belt conveyor (24) for movement into a second vacuum lamination chamber (20) of the vacuum laminator, said second chamber being arranged in-line with said first chamber (18), said second chamber being defined by an upper platen (152) and a lower platen (148) adapted to be moved into sealing engagement, the second belt conveyor having an endless belt (72) under tension that has an aperture (76) therein and is characterized in having an initial or set-point position such that, as the board is moved on the endless belt into the region of the second vacuum chamber between the upper and lower platens, the aperture is moved into alignment with and between the board and the lower platen (148);

(j) continuing the movement of the first endless belt (70) to the initial or set-point position for acceptance of a new prelaminated board or substrate arriving at the entrance end of the first vacuum chamber (18);

(k) sensing the positioning of the evacuated board or substrate (200a) in the second vacuum chamber (20) and stopping the movement of the second belt conveyor (24);

(l) relieving the tension on the endless belt (72) of the second belt conveyor (74);

(m) lifting the lower platen (148) in the second vacuum chamber up through the aperture (76) in the endless belt (72) into sealing engagement with the upper platen (152) and thereby capturing within the second vacuum chamber the board or substrate and the portion at least of the endless belt upon which the board or substrate is positioned;

(n) evacuating the second vacuum chamber (20);

(o) heating the upper platen (152) and the lower platen (148) of the second vacuum chamber to a temperature at which the laminate on the board or substrate has a high flow characteristic;

(p) causing the upper platen (152) to apply mechanical pressure on the board or substrate to force the heated laminate to conform closely to the surface contours of the board or substrate;

(q) when the aforesaid lamination is complete, allowing atmospheric air to enter the second vacuum chamber (20);

(r) lowering the lower platen (148) of the second vacuum chamber down through the aperture (76) in the endless belt (72) of the second belt conveyor (24);

(s) restoring the tension in the endless belt (22) of the second belt conveyor for movement of the laminated board or substrate out of the vacuum laminator (12);

(t) conveying the board or substrate out of the vacuum laminator; and

,

(u) continuing the movement of the second endless belt (72) to the initial or set-point position for acceptance of a new board or substrate exiting from the first vacuum chamber (18) and arriving at the entrance end of the second vacuum chamber (20).

6. A method according to claim 5 further including:

(v) placing on the entrance end of the first conveyor belt (70) a second prelaminated printed circuit board or other substrate (200b); and

,

(w) repeating steps (a) through (u).

7. A method according to claim 6 wherein in (v) the second prelaminated board or substrate (200b) is placed on the entrance end of the first conveyor belt (70) substantially at the same time step (m) is occurring with respect to the first board or substrate, to enable the vacuum lamination cycle in each vacuum chamber (18,20) to be operated in alternating sequence, thereby allowing at least one prelaminated board to be in each chamber at the same time.

8. A method according to claim 5 further including the following steps, before step (a):

(a.i) conveying on a first input conveyor (14) a prelaminated board or substrate (200a) from preceding equipment towards the first belt conveyor (22);

(a.ii) providing a barrier (30) at the exit end of the first input conveyor (14) to stop the movement of the board or substrate and to align the board or substrate;

(a.iii) sensing the presence of the board or substrate at the exit end of the first input conveyor (14) and stopping the movement of the first input conveyor;

(a.iv) adjusting the barrier (30) at the exit end of the first input conveyor to a non-stopping or non-blocking position; and

,

(a.v) conveying the board from the first input conveyor to the entrance end of the first belt (70) for movement of the board or substrate into the first vacuum chamber.

9. A method according to claim wherein the dry film is a solder mask or a primary imaging photoresist.

10. Apparatus for vacuum laminating a dry film photoresist-forming layer onto a prelaminated printed circuit board or other substrate which prevents premature tacking of the dry film to the board or substrate, comprising:

a vacuum laminator (12) having two independent vacuum lamination chambers (18,20);

the first vacuum lamination chamber (18) being operated at ambient temperature while a vacuum is drawn to evacuate all of the air between the loosely applied prelaminated dry film and the surface of the board or substrate, thereby to place the dry film in intimate contact with the board or substrate without causing the dry film to prematurely adhere to the surface before all of the air can be evacuated; and

,

the second vacuum lamination chamber (20) being operated under heat and mechanical pressure to laminate the evacuated dry film to the board or substrate, thereby to ensure complete conformance of the dry film to the surface contours of the board or substrate.

11. Apparatus according to claim 10 wherein the first and second vacuum lamination chambers (18,20) are disposed in end-to-end relation.

12. Apparatus according to claim 11 wherein the first and second vacuum lamination chambers (18,20) are conveyorized to allow for operation in a continuous and automated fashion.

13. Apparatus according to claim 12 wherein the first and second vacuum lamination chambers are operable in alternating sequence.

14. Apparatus according to claim 13 wherein the second vacuum lamination chamber (20) includes a dual conveyor belt system.

15. Apparatus according to claim 14 wherein the first chamber (18) has a relatively stationary upper platen (150) and a lower platen (146) that is adapted to be moved up into sealing engagement with said upper platen to form the first vacuum chamber region, and a first belt conveyor (22);

the first belt conveyor having an entrance end (22a) and an exit end and being positioned in operative relationship with said first vacuum lamination chamber (18) such that, when moved from a set-point position thereof with a prelaminated board or substrate placed on the entrance end thereof, the board is moved into the first vacuum chamber region between the upper and lower platens (150,146), said first belt conveyor including an endless belt (70) under tension upon which the board or substrate (200) is placed at the entrance end (22a) of the first belt conveyor and having an aperture (74) therein so positioned with respect to the entrance end of the first belt conveyor such that, as the board is moved into the region of the first vacuum chamber between the upper and lower platens (150,146), the aperture is moved into alignment between the board or substrate and the lower platen;

wherein the apparatus further comprises;

a first motor (78) is operative to cause said belt (70) to move with a board or substrate (200) placed on the entrance end of the first belt conveyor (22) thereby to position said board or substrate in the region of the first vacuum chamber (18);

a first sensor (142) is arranged to provide a signal responsive to the movement of said belt required to position the board or substrate in the region of the first vacuum chamber for stopping said first motor (78) from causing further such movement;

a first tension adjuster (134) operative to relieve the tension of said endless belt (70) of said first belt conveyor (22);

a first lift (202) operative to lift the lower platen (146) of the first vacuum chamber up through the aperture (74) in the belt (70) into sealing engagement with the upper platen (150) thereby to capture the board or substrate and the portion, at least, of the belt upon which the board or substrate is positioned within the first vacuum chamber;

a first vacuum pump (186) to evacuate the first vacuum chamber (18);

wherein the second vacuum lamination chamber (20) has a relatively stationary upper platen (152) and a lower platen (148) that is adapted to be moved up into sealing engagement with said upper platen to form the second vacuum chamber region and a second belt conveyor (24);

the second belt conveyor having an entrance end and an exit end and being positioned in operative relationship with said second vacuum lamination chamber (20) such that, when moved from a set-point position thereof with a prelaminated board or substrate (200) placed on the entrance end thereof, the board is moved into the second vacuum chamber region between the upper and lower platens, said second belt conveyor including an endless belt (72) under tension upon which the board or substrate is placed at the entrance end of the second belt conveyor and having an aperture (76) therein so positioned with respect to the entrance end of the second belt conveyor (24) such that, as the board is moved into the region of the second vacuum chamber between the upper and lower platens (152,158), the aperture is moved into alignment between the board or substrate and the lower platen (148);

a second motor (80) operative to cause said belt to move with a board or substrate placed on the entrance end of the second belt conveyor thereby to position said board or substrate in the region of the second vacuum chamber (20);

a second sensor (144) providing a signal responsive to the movement of said belt (72) required to position the board or substrate in the region of the second vacuum chamber for stopping said second motor (80) from causing further such movement;

a second tension adjuster (136) operative to relieve the tension of said endless belt (72) of said second belt conveyor (24);

a second lift (204) operative to lift the lower platen (148) of the second vacuum lamination chamber up through the aperture (76) in the belt (72) into sealing engagement with the upper platen (152) thereby to capture the board or substrate and the portion, at least, of the belt upon which the board or substrate is positioned within the second vacuum chamber;

a second vacuum pump (186″

) to evacuate the second vacuum chamber;

a heater (190″

,192,″

) for heating the upper platen (152) and the lower platen (148) of the second vacuum lamination chamber (20) to a temperature at which the dry film laminate on the board has a high flow characteristic;

a mechanical press for causing the upper platen (152) of the second vacuum laminator to exert mechanical pressure on the board to cause the dry film to completely conform to the surface of the board or substrate; and

,

a controller (198) responsive to the signal provided by said first sensor (142) to control said first motor (78), first tension adjuster (134), first lift (202), and first vacuum pump (186′

), and also responsive to the signal provided by said second sensor (144) to control said second motor (80), second tension adjuster (136), second lift, second vacuum pump (186″

), heater (190″

,192″

) and mechanical press.

16. Apparatus according to claim 15 further including in each of the two vacuum lamination chambers (18,20):

a first passage communicating between said vacuum chamber and said vacuum pump controlled by said controller (198) for evacuating said vacuum chamber; and

,

a second passage communicating between said vacuum chamber and atmospheric air controlled by said controller for allowing air at atmospheric pressure to enter the vacuum chamber at the completion of the vacuum lamination cycle in each chamber;

said controller then being operative to actuate said lift (202,204) to lower said lower platen (146,148) down through the aperture (74,76) in the belt (70,72), to actuate said tension adjuster (134,136) to restore the tension of the belt, and to actuate said motor (78,80) to move the processed board (200) out of the region of the respective vacuum chamber.

17. Apparatus according to claim 16 wherein the upper platen (152) of the second vacuum chamber includes a diaphragm (176″

) that is substantially impervious to air and forms the ceiling of the second vacuum chamber, and further including;

a third passage (194′

) communicating between said vacuum pump (186″

) and the space between said diaphragm and the upper platen and controlled by said controller (198) for evacuating said space; and

,

a fourth passage (194″

) communicating between the space between said diaphragm and the upper platen and air, controlled by said controller to allow air at atmospheric pressure or compressed air to enter such space, before atmospheric air is allowed to enter the vacuum chamber through said second passage, to cause the diaphragm to slap down and apply mechanical pressure on the board to force the laminate to conform closely to the surface contours of the board or substrate.

18. Apparatus according to claim 15 further including:

a third sensor (170) providing a signal responsive to the board moving off the first belt conveyor (22) at the exit end thereof for causing said first motor (78) to continue the movement of the belt (70) to the set-point position of the belt conveyor;

a fourth sensor (166) providing a signal responsive to the approach of the belt to the set-point position of the first belt conveyor to cause said first motor to slow down the movement of the belt to the set-point position;

a fifth sensor (158) providing a signal responsive to the movement of the belt (70) to the set-point position of the belt conveyor (22) to cause said first motor to stop the first belt conveyor with the belt at the set-point position;

a sixth sensor (172) providing a signal responsive to the board moving off the second belt conveyor (24) at the exit end thereof for causing said second motor (180) to continue the movement of the belt (72) to the set-point position of the belt conveyor;

a seventh sensor (168) providing a signal responsive to the movement of the belt to the set-point position of the belt conveyor to cause said second motor to stop the second belt conveyor with the belt at the set-point position; and

,

an eighth sensor (160) providing a signal responsive to the movement of the belt to the set-point position of the belt conveyor to cause said second motor to stop the second belt conveyor with the belt at the set-point position.

19. Apparatus according to claim 15 further including:

an infrared sensor (174) at the exit end of the second vacuum chamber for measuring the temperature of the laminated board exiting from the second vacuum chamber and for providing a signal to cause the platen heaters to raise or lower the lamination temperature in the second chamber.

20. Apparatus according to claim 15 further including:

a first input conveyor (14) arranged in end-to-end relation with the first vacuum lamination chamber (18) and driven under the control of said controller (198) by said first motor (78), said first input conveyor having an entrance end and an exit end and being operative to convey prelaminated boards from preceding equipment to the entrance end of said first belt conveyor (22);

a first movable barrier (30) at the exit end of said first input conveyor, said barrier having a hoard blocking position and a board non-blocking position with said first barrier being in the board blocking position;

a photosensor (36) for sensing a board (200) at the exit end of said first input conveyor, said photo sensor producing a signal in response to the presence of a board at the exit end of the first input conveyor to cause the controller to stop the movement of said first input conveyor and to adjust said barrier to a non-blocking position, following which said controller causes the first motor to start both the first input conveyor and the first belt conveyor to load the board onto the entrance end of the first belt conveyor.