WO2002003765A2

WO2002003765A2 - Method and apparatus for locating and securing a printed wire board on a screen printer

Info

Publication number: WO2002003765A2
Application number: PCT/US2001/020453
Authority: WO
Inventors: Mark A. Wright
Original assignee: Honeywell International Inc.
Priority date: 2000-06-30
Filing date: 2001-07-25
Publication date: 2002-01-10
Also published as: WO2002003765A3; AU7152901A; TW506240B

Abstract

An apparatus and method to locate and secure a printed wire board (PWB) to the work surface of a machine in a predicable and repeatable manner. A base plate (10) having a series of equally spaced tapped holes (20) and also having series of equally spaced holes (40) inter-spaced relative to the tapped holes (20) all of which are located centrally to the center of the work surface are used to fix and locate either a PWB carrier (60) or a combination of adjustable clamping mechanisms (130) relative to the center of the machine's axis. The bottom surface (61) of the PWB carriers (60) are designed with non-movable mechanical appendages or dowel pins (70) that engage corresponding holes (40) located in the work surface. By means of mechanical association, each carrier (60) is located to the work surface in a repeatable manner. The top surface (62) of the carrier (60) is customized to fit each PWB as required. The carrier (60) is then securely fastened to the work surface. Once the carrier (60) or adjustable clamp assembly (130) is fixed to the work surface, the PWB is then placed into the holder and fastened to the carrier (60). The PWB is secured and located in a fixed known location relative to the machine's central axis and ready for further processing.

Description

BACKGROUND OF THE INVENTION Field of the Invention (Technical Field):

METHOD AND APPARATUS FOR LOCATING AND SECURING A PRINTED WIRE

BOARD ON A SCREEN PRINTER

The present invention relates to circuit card assembly and manufacturing and more particularly to a method and apparatus to locate and secure a printed wire board (PWB) on a machine's work surface.

Background Art:

When a PWB is ready to have solder paste applied to its surface, prior to the actual surface mount components being placed on the board, the board must be secured and located to a specific fixed position on an solder paste application machine.

Prior devices used to locate and secure a printed wire board (PWB) to a machine's work surface are cumbersome, hard to use, labor intensive, and not locate boards accurately or repeatedly to the same location on the machine's work surface. Up to 2 hours are required to setup a single board prior to the application of solder paste. Considerable effort is also required after the initial setup is finished to run any subsequent boards because of the ineffectiveness of the locating method employed by the prior art devices.

Prior art devices consist of 2 flat bars about 1 inch square with channels cut into each bar housing and air operated "flippers" that secure a board in the vertical position while the board is located, by its edges, to a fixed position in the x, y axis. After it is located, horizontal air driven clamps are engaged to hold and locate the board by its edges. The "flippers" are then retracted exposing the top surface fully for the application of solder paste via a solder paste screen and wiper method.

Other prior art devices use a worktable surface that incorporates a series of drilled and tapped holes located on a grid pattern. These are used to secure the original equipment manufacturer's (OEM's) bar clamp assembly to the work surface. The location of the bar clamp assembly is based on the size and shape of the PWB. Once the bars are roughly located and fixed to the work surface, a labor intensive, manual process of precisely locating the bar system is used. It is necessary to precisely locate the clamp system so that the PWB is centrally located in relation to the center of the work surface. The bar clamp method is cumbersome to use. It requires a large amount of time to get the original setup aligned properly in relationship to the machine axis and centrally located to the work surface. Also, once the clamp assembly is located and fixed accurately to the work surface, there is no guarantee that the subsequent boards are located to the same fixed location relative to the machine axis within the specified positional tolerance required to produce quality PWBs in terms of solder paste applied to the correct locations across the entire board surface. Some machines employ cameras and software that locate and position a board automatically based on known artifacts contained within the board. This method is used on higher priced machines. Other machines designed primarily for volume production utilize a conveyor system combined with cameras and software to locate and hold a board. This system is automatic in operation and requires little operator intervention once the initial setup is complete. However, this device requires a time consuming set up procedure and is used primarily for high volume production. These higher volume machines utilizing conveyor systems backed by camera and software are disadvantageous because of the initial high cost of the machine and the longer changeover time required to change from one board design to the next. In low volume/high mix facilities, one of the most costly areas of operation is the time it takes to change over from building one design to the next.

The prior art devices fail to position and secure a PWB to the work surface on a repeatable basis within acceptable tolerance limits as specified by the specific machine. They also take an extremely long time to get the initial setup finished. SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)

Disclosed is an apparatus for locating more than one similar PWBs on a solder paste application machine comprising at least two locating protrusions on a carrier, at least two locating apertures on a base plate of the solder paste machine corresponding to the at least two locating protrusions, a fastening structure for removably affixing the carrier to the base plate and a clamping apparatus for clamping the more than one similar PWB in substantially the same position on the carrier. The at least two locating protrusions preferably comprise dowel pins. The at least two locating apertures preferably comprise a grid pattern. The preferred fastening structure comprises at least one fastening aperture on the base plate and a fastener inserted through a corresponding aperture in the carrier. The preferred fastener comprises a threaded bolt. The preferred clamping apparatus comprises an edge nesting structure. The preferred edge nesting structure comprises at least two pins and a an apparatus for pushing the more than one similar PWB against the at least two pins and for pushing the more than one similar PWB against the carrier. The preferred pushing mechanism comprises a cam lock. The apparatus can also have at least one scribed line on the base plate and at least one scribed line on the carrier for a visual aid in locating the carrier on the base plate. Also disclosed is an adjustable clamping apparatus for locating and affixing a PWB to a base plate of a solder paste application machine comprising at least two locators affixed to a base plate, each locator

^• comprising a protrusion for locating the PWB in a predetermined location and at least one clamp for pushing an edge of the PWB against the protrusions and pushing the PWB against a top edge of the at least one clamp and a top edge of the at least two locators. The preferred at least two locators comprise slots for adjustably affixing the at least two locators on the base plate. The preferred at least one clamp comprises a slot for adjustably affixing the at least one clamp on the base plate. The at least one clamp for pushing the PWB against the protrusions and pushing the PWB against a top edge of the at least one clamp and a top edge of the at least two locators comprises at least one cam lock. The apparatus can also comprise at least one scribed line on the base plate for a visual aid in locating an approximate center of the PWB on the base plate.

The preferred method for locating more than one similar PWBs on a solder paste application machine comprises the steps of inserting protrusions in a carrier plate into corresponding apertures in a base plate to locate the carrier in a predetermined location, affixing the carrier to the base plate and affixing the PWB on the carrier comprising the sub steps of pushing the PWB against at least two protrusions affixed to the carrier and simultaneously pushing the PWB against the top surface of the carrier. The method can also comprise the step of aligning scribed lines in the base plate with scribed lines in the carrier.

Also disclosed is a method of locating and clamping a PWB to a base plate of a solder paste application machine, comprising the steps of affixing at least two locators to the base plate at predetermined locations and pushing the PWB against a protrusion on each of the locators and simultaneously pushing the PWB against an edge of the at least two locators and an edge of at least one clamp. The step of pushing can also comprise the step of locking a position of the PWB. The method can also comprise the step of aligning scribed lines on the base plate with an approximate center of the PWB.

A primary object of the present invention is to provide a simple way of locating and securing a PWB to a work surface.

Another object of the present invention is to provide low volume/high mix production lines with an inexpensive means to reliably locate and secure PWBs.

Yet another object of the present invention is to provide a locating and mounting apparatus for PWBs within a specified positional tolerance. Another advantage of the present invention is that the position of the PWB is maintained within a specified tolerance due to the unique hole and dowel pin design.

A primary advantage of the present invention is that it is easier to use, more precise, faster, and more reliable than the prior bar clamp and software aided devices.

Another advantage of the present invention is that it is much easier to maintain having few moving parts.

Yet another advantage of the present invention is that due to its inherent non-complexity it will last a long time.

Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate several embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating a preferred embodiment of the invention and are not to be construed as limiting the invention. In the drawings:

Fig. 1 is depicts a preferred base plate. Fig. 2 is a perspective view of the base plate of Fig. 1

Fig. 3 is a top view of the preferred carrier.

Fig. 4 is a side view of the carrier of Fig. 3.

Fig. 5A shows the preferred main clamp assembly.

Fig. 5B shows a sectional view of Fig. 5A. Fig. 6 is a perspective view of the main clamp assembly of Fig. 5.

Fig. 7 shows the preferred auxiliary clamp assembly.

Fig. 8A shows the preferred locators.

Fig.δB shows a side view of Fig. 8A.

Fig. 9A shows a PWB mounted on the carrier. Fig. 9B shows a side view of Fig. 9A.

Fig. 10 shows a PWB and carrier mounted to the base plate.

Fig. 11 is a perspective view showing an engineering PWB mounted to the base plate using the adjustable clamp and locator assembly.

Fig. 12 shows the preferred washer component. Fig. 13 is a perspective view of the locators shown in Fig. 8A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING OUT THE INVENTION)

The present invention uses a pallet system to mount and un-mount PWBs to a solder paste application machine. Referring to Figs. 1 and 2, base plate 10 is preferably made of aluminum or similar material of a size that corresponds with the size of the machine's worktable dimensions. Its thickness is dependent on the design of the PWB carrier thickness. Base plate 10 has a series of equally spaced fastening apertures 20 that are relative to the x-y center 30 of base plate 10. Interspersed between fastening apertures 20 is a series of equally spaced locating apertures 40 on a similar grid pattern relative to x-y center 30. The base plate's 10 x-y plane is plainly marked with a scribed line 50 in two directions that provides a visual reference to the center of the plane in an x-y direction. Base plate 10 is securely fastened to the work surface of the solder paste application machine, maintaining a relative location to the machine's x-y axis center.

Figs. 3, 4, 9A, and 9B show PWB carrier 60 which is also preferably made of an aluminum plate of various x-y dimensions in a proportion that is larger than the PWB it is to locate and secure. The thickness, or z dimension, is of a fixed dimension based on the total stackup of the machine for which this apparatus is custom designed. On the bottom surface 61 of the carrier 60 are two protruding cylindrical forms 70 that are of a size smaller in diameter than the matching locating apertures 40 in the base plate 10. Fig. 4 shows the preferred protruding cylindrical form. Referring back to Fig. 3, these cylindrical forms 70 are located centrally from the x-y plane centerline of the carrier 60 and on the same dimensional base plate grid pattern 40. On the top surface 62 of the carrier 60 are a series of counter bored holes 80 matching the characteristics of the fasteners 90 used to secure the carrier 60 to the base plate 10. The top surface 62 also has engraved lines 65 central to the x-y axis used as an aid to locate the carrier to the base plate 10 by aligning the lines 65 to the base plate 10 engraved lines 50. Carrier 60 has protrusions 100 that function as a method to locate a PWB to the surface of the carrier 60. Protrusions 100 are arranged to locate the PWB in a known position, parallel to the x axis and centrally located to the carrier 60. Protrusions 100 are shorter in height than the thickness of the PWB it is to locate. Carrier 60 also has one or more cam action hexagon shaped clamps 110 and fasteners 120, such as Jergens Micro Clamps, located on the carrier's 60 top surface. The hexagon shaped clamp mechanism 110 secures the PWB to carrier 60 when its fastener 120 is rotated, applying lateral force to the PWB forcing the PWB against the protrusions 100, simultaneously locating and securing the PWB to carrier 60. Fig. 9A shows a top view and Fig. 9B shows a side view of the carrier 60 with a PWB mounted in place.

Another component used to locate engineering PWBs is an adjustable clamping mechanism as shown in Figs. 5, 6, 7, 8A, 8B, and 13. A perspective view showing the preferred method of using the adjustable clamping mechanism is shown in Fig. 11. The preferred adjustable clamping mechanism has the following components:

Figs. 5 and 6 show the main clamp assembly 130, Fig. 7 shows the auxiliary clamp assembly 140, and Fig 8A shows a top view of the right hand locator assembly 150 and left hand locator assembly 160 which are mirror images. A side view of the right locator is shown in Fig. 8B for clarity. The main clamp assembly preferably comprises of an aluminum, or similar, base 170 of substantially the same thickness as carrier 60 with a series of counter bored slots 175 that accept two or more fasteners 90 and two or more washers 180. A series of tapped holes accept one or more clamp mechanisms 110 and 120.

The auxiliary clamp assembly 140 follows the same characteristics as the main clamp assembly 130, using the same components with the base 170 halved in size to form a new base 190.

The right-hand locator 200 and left-hand locator 210, a mirror image of right-hand locator 200, shown in Figs. 8A, 8B, and 13, are preferably made from a rectangular piece of aluminum, or similar material, with a counter bored slot 205 accepting a fastener 90 and a washer 180. The locators 200 and 210 are substantially the same thickness as carrier 60 and have a protrusion 220 on the top surface 215 to facilitate the location of the PWB. Operation of the adjustable clamp assembly to locate a PWB to the base plate 10 is shown in Fig. 11. Locators 200 and 210, main clamp assembly 130, and auxiliary clamp assemblies 140 are arranged on base plate 10 in such a manner as to centrally locate the PWB to the base plate 10, aligning the PWB parallel to the machine axis. This alignment is manually accomplished using scribed lines 50 as a visual aid to locate the approximate center of the PWB to the base plate 10. The locators 200 and 210, main clamp assembly 130, and the auxiliary clamp assemblies 140 are secured to the base plate 10 using washers 180, shown in Fig. 12, and fasteners 90. Generally, the locators 200 and 210, a mirror image of locator 200, are located opposite of the main clamp assembly 130 using the cam action of the clamp mechanisms, fastener 120 and hexagon shaped clamp 110 to apply lateral force to the PWB securing the PWB against the raised protrusions 220 of the locators 200 and 210, a mirror image of locator 200.

Operation of a carrier 60 is depicted in Figs. 9A and 9B prior to being located and fastened to the base plate 10. Fig. 10 depicts a PWB mounted on a carrier 60, mounted on the base plate 10. Fig. 10 describes the general configuration of the apparatus when it is used in its preferred state. As shown in Fig. 9A, protrusions 100 are used to locate a PWB centrally to carrier 60 and clamped into position by fastener 120 and hexagon clamp 110. Next, the carrier 60 is located, visuallyby aligning engraved lines 65 on carrier 60 to the engraved lines 50 on base plate 10. Once the carrier 60 is aligned, the protrusions 70 of the carrier 60 are inserted into locating aperture 40 of the base plate 10 for final alignment of the carrier 60 to the base plate 10. Fasteners 90 are then inserted into aperture 80 of the carrier 60 and fastened to the base plate 10 fastening aperture 20.

In an alternative embodiment, the size and grid pattern of the base plate 10 is changed to meet specific requirements with corresponding changes made in carrier 60. The thickness of the base plate 10 and the carrier 60 can be varied to suit a particular implementation. The protrusions 100 used to locate a PWB can be designed to suit a particular application. Carrier 60 can be modified with various apertures such as slots and holes and in various shapes to facilitate different PWB board designs, including double- sided board layouts. The cylindrical forms 70 that are used to locate the carrier 60 to the base plate 10 may vary in size to match a particular application. The carrier 60 configuration can be changed to meet the demands and designs of each separate PWB configuration. The distance between the protrusions 70 can be varied depending on the overall size of each carrier 60 but the distance is based on spacing of the grid pattern 40 on the base plate 10.

The relationship between the base plate 10 grid pattern fastening apertures 20 and locating apertures 40 must be the same as the carrier 60 protrusions 70 and mounting holes 80. The grid pattern apertures 20 and 40 must be located centrally to the solder paste machine's x-y center. The difference in size of the protrusions 70 must be smaller than 20 and be within a range that allows the solder paste machine's PWB locating software to function properly.

The adjustable clamp mechanism could be omitted if a carrier is designed for each PWB. The function of the adjustable clamp mechanism is to provide flexibility in supporting engineering functions when designing new PWB layouts and building one or two boards at a time. It eliminates the cost of designing and building a custom carrier for one board design.

The present invention substantially reduces the amount of time it takes to locate a PWB on the work surface of a solder paste application machine.

The estimated time savings of 90 minutes per each setup when compared to existing systems. The location of each subsequent board loading is repeatable and requires less than 60 seconds to load and unload.

Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above, are hereby incorporated by reference.

Claims

CLAIMS What is claimed is:

1. An apparatus for locating more than one similar PWBs on a solder paste application machine, the apparatus comprising: at least two locating protrusions on a carrier; at least two locating apertures on a base plate of the solder paste machine corresponding to said at least two locating protrusions; a fastening structure for removably affixing said carrier to said base plate; and a clamping apparatus for clamping the more than one similar

PWBs in substantially the same position on said carrier.

2. The invention of claim 1 wherein said at least two locating protrusions comprise dowel pins.

3. The invention of claim 1 wherein said at least two locating apertures comprise a grid pattern.

4. The invention of claim 1 wherein said fastening structure comprises at least one fastening aperture on said base plate and a fastener inserted through a corresponding aperture in said carrier.

5. The invention of claim 4 wherein said fastener comprises a threaded bolt.

6. The invention of claim 1 wherein said clamping apparatus comprises an edge nesting structure.

7. The invention of claim 6 wherein said edge nesting structure comprises at least two pins and an apparatus for pushing the more than one similar PWBs against said at least two pins and for pushing the more than one similar PWBs against said carrier.

8. The invention of claim 7 wherein the apparatus for pushing the more than one similar PWB against said at least two pins and for pushing the more than one similar PWB against said carrier comprises a cam lock.

9. The invention of claim 1 further comprising at least one scribed line on said base plate and at least one scribed line on said carrier for a visual aid in locating said carrier on said base plate.

10. An adjustable clamping apparatus for locating and affixing a PWB to a base plate of a solder paste application machine, the apparatus comprising: at least two locators affixed to a base plate each comprising a protrusion for locating the PWB in a predetermined location; and at least one clamp for pushing an edge of the PWB against said protrusions and pushing the PWB against a top edge of said at least one clamp and a top edge of said at least two locators.

11. The invention of claim 10 wherein said at least two locators comprise slots for adjustably affixing said at least two locators on said base plate.

12. The invention of claim 10 wherein said at least one clamp comprises a slot for adjustably affixing said at least one clamp on said base plate.

13. The invention of claim 10 wherein said at least one clamp for pushing the PWB against said protrusions and pushing the PWB against a top edge of said at least one clamp and a top edge of said at least two locators comprises at least one cam lock.

14. The invention of claim 10 further comprising at least one scribed line on said base plate for a visual aid in locating an approximate center of the PWB on said base plate.

15. A method for locating a more than one similar PWB on a solder paste application machine, the method comprising the steps of: a) inserting protrusions in a carrier plate into corresponding apertures in a base plate to locate the carrier in a predetermined location; b) affixing the carrier to the base plate; and c) affixing the PWB on the carrier comprising the sub steps of: i) pushing the PWB against at least two protrusions affixed to the carrier; and ii) simultaneously pushing the PWB against the top surface of the carrier.

16. The method of claim 15 further comprising the step of aligning scribed lines in the base plate with scribed lines in the carrier.

17. A method of locating and clamping a PWB to a base plate of a solder paste application machine, the method comprising the steps of : a) affixing at least two locators to the base plate at predetermined locations; and b) pushing the PWB against a protrusion on each of the locators and simultaneously pushing the PWB against an edge of the at least two locators and an edge of at least one clamp.

18. The method of claim 17 wherein the step of pushing further comprises the step of locking a position of the PWB.

19. The method of claim 17 further comprising the step of aligning scribed lines on the base plate with an approximate center of the PWB.