WO2000068010A1

WO2000068010A1 - Cartridge squeegee system with floating paste retainers

Info

Publication number: WO2000068010A1
Application number: PCT/US2000/012327
Authority: WO
Inventors: Mark Curtin
Original assignee: Transition Automation, Inc.
Priority date: 1999-05-06
Filing date: 2000-05-05
Publication date: 2000-11-16

Abstract

A cartridge squeegee head (30) for solder paste stencil printing machines is provided having first and second squeegee blades (32a, 32b) fixedly secured to a coupling block (36). Flexible retaining walls (44a, 44b) are mounted at each end of the coupling block to enclose the edges of the squeegee blades (32a, 32b) and define a sealed chamber for the solder paste. Further, pressure bars (12a, 12b) are provided to engage the cartridge and apply force to the squeegee blade edges.

Description

1 Title

Cartridge Squeegee System with Floating Paste Retainers

Background of the Invention Field of the Invention The invention relates to a cartridge squeegee head for a solder paste applicator.

Description of the Relevant Art

State-of-the-art solder paste printing machines typically have two squeegee blades attached to a translation head which is generally referred to as a cartridge squeegee head. This head has bearing elements which are connected to linear rods located above a stencil. There is a driving mechanism which drives the squeegee head back and forth along the linear rods and there are vertical actuators to bring each squeegee blade into contact with the stencil during the print stroke. A difficulty with these machines is the control of the solder paste which attaches to every surface it contacts. Typical difficulties of most prior art machines are described in U.S. Pat. 5,791,243. The squeegee head described in this patent overcame many of the problems of the then prior art squeegee heads. The squeegee head in this patent basically contained the solder paste in a substantially hemetically sealed, contamination-free chamber defined by the two squeegee blades, by paste retainer walls at the ends of the squeegee blades and a stencil foil. The squeegee head in the '243 patent effected a tilting and locking sequence.

The squeegee head disclosed herein, in addition to other advantages, does not require a tilting and locking sequence.

Summary of the Invention

The cartridge squeegee head of the invention embodies a floating paste retainer assembly which enables slight motion and tipping without the squeegee blades loosing contact with the stencil. That is, the squeegee head is operated with both squeegee edges touching the stencil surface at all times thereby eliminating the exposure of the solder paste to ambient air. In that the prior art locking and tilting apparatus is eliminated, the squeegee head of the invention can be made smaller which allows the system to be more easily retrofit into existing equipment.

Broadly, the invention comprises a cartridge squeegee head for solder paste 2 printing machines having first and second squeegee blades fixedly secured to a coupling block. Pressure bars are adapted to engage the cartridge in which the squeegee blades are secured. The force applied by each pressure bar is distributed across the edge of the squeegee blade. Flexible retaining walls enclose the edges of the squeegee blades. The cartridge head, the squeegee blades and the retaining walls define a sealed chamber for the solder paste.

The force of the pressure bar is located close to the line of the actual active squeegee edge thereby transferring most of the force to that squeegee edge. This allows the squeegee head to slide along the stencil with most of the contact force made at the squeegee edge which is in a non-binding angle of attack. The other squeegee edge receives minimal downward force which allows it to float along the non-smooth surface of the stencil even though this squeegee edge has a binding angle of attack.

Brief Description of the Drawings

Fig. 1 is an illustration, partly broken away, of an end view of a cartridge squeegee system;

Fig. 2 is a perspective view of a cartridge squeegee head of the invention; and Fig. 3 is an illustration of the cartridge squeegee system with pressure bars engaging the cartridge head.

Description of the Preferred Embodiment(s) Referring to Figs. 1 and 3, a squeegee system is shown generally at 10 together with solder paste P and a stencil S. Vertically actuated pressure bars 12a and 12b are mounted to a translation head 14, which head 14 travels on linear rods 16 (only one shown). The pressure bars 12 have a vertical movement with respect to the rods 16. Bearing guided air cylinders 18a and 18b are used to effect the vertical motion. The pressure bars 12a and 12b each comprise earning or guide surfaces 20a and 20b, horizontal bearing surfaces 22a and 22b and vertical bearing surfaces 24a and 24b.

Referring to Figs. 1 and 2, a cartridge squeegee head 30 comprises two squeegee blades 32a and 32b having edges 34a and 34b respectively which engage the stencil S. A coupling block 36 has a N-shaped groove 38. The top of the block 36 is characterized by a pair of parallel raised bearing surfaces 40a and 40b and vertical bearing surfaces 42a and 42b. At either end of the block 36 are spring loaded retaining walls shown generally at 44a and 44b, only one, 44b, shown in detail. The walls 44 function in combination with the squeegee blades 32 and block 36 to close solder paste P so that it has minimal exposure to ambient air. Leaf springs 48a and 48b are fastened to the block 36 between the bearing surfaces 40 and extend beyond the lateral 5 edges of the blades 32. The springs 48 can be fastened such as with threaded fasteners 50.

The retaining wall 44b has slots 52b and are slidably secured to the sides of the block 36 by fasteners 54b. The retaining wall 44a is identical. The upper edges of the walls 44 engage the springs 48 and extend beyond the ends of the squeegee blades 32.

10 The walls 44 are biased against the stencil S by the springs 48. This allows relative movement of the head (slightly pivot).

Broadly, the use of two-bladed squeegee cartridges with associated pressure bars to control the time sequence and pressures applied to squeegee blade edges are generally well known in the art.

15 In the operation of the invention, referring to Fig. 3, if the squeegee blade 32a is to be driven through a print stroke, the pressure bar 12a engages the bearing surface 40a. The cammed surface 20a ensures that the pressure bar 12a will properly slide by and engage the surface 40a. Similarly, the pressure bar 12b also engages the bearing surface 40b. The pressure applied on the surface 40a ensures that the blade edge 34a

20 stays engaged with the stencil S in the print stroke. The pressure bar 12b only lightly engages the surface 40b to ensure that the edge 34b of the squeegee blade 32b only remains in floating engagement with the stencil S. The pressure bar 12a drives the squeegee head 30 across the stencil S with the pressure bar 12a engaging the bearing surface 42a. When the print stroke is complete then pressure is transferred to the edge

25 34b of the squeegee blade 32b by the pressure bar 12b and the pressure applied to the edge 34b of the squeegee blade 32b is released and the print stroke is reversed.

The force of the pressure bar 12 is located close to the line of the associated active squeegee edge 34. Most of the force is transferred to the squeegee edge 34 during the print stroke. This allows the squeegee head 30 to slide along the stencil S

30 with most of the contact force made at the squeegee edge 34 which is at a non-binding angle of a attack. The other squeegee edge 34 receives minimal downward force which allows it to float along the non-smooth surface of the stencil S even though this 4 squeegee edge 34 has a binding angle of attack. Typically, the squeegee blades are at a nominal standing angle at 60°. The squeegee blades 32 are essentially locked by the geometry of the pressure bars 12 in the direction of push and the sliding freedom of motion of the head. The two spring loaded retaining walls 44 are situated at each end of the block

36 to close the solder paste. The spring action of the retaining walls 44 presses their bottom edges into contact with the stencil surface. As the squeegee head is activated, there is expectedly some flexing and small movements. The squeegee edges 34 and the bottom edges of the walls 44 remain in contact at all times with the stencil S even as the cartridge head tilts and shifts during operation. With the squeegee head of the invention, both squeegee edges 34 touch the surface stencil at all times, thereby eliminating the exposure of the solder paste to ambient air. The retaining walls enable slight motion and tipping without loosing contact with the stencil.

The foregoing description has been limited to a specific embodiment of the invention. It will be apparent, however, that variations and modifications can be made to the invention, with the attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention. Having described my invention, what I now claim is:

Claims

1. A cartridge squeegee head for solder paste printing machines which comprises: a first squeegee blade fixedly secured to a coupling block, the blade having an edge and ends, the blade adapted to wipe a stencil; means for applying pressure to said first squeegee blade during a print stroke, the blade having an edge and ends, the edge of the blade in contact with the stencil foil; means for flexibly closing the ends of the squeegee blade, the means for flexibly closing defining with the squeegee blade and the coupling block a sealed chamber in which chamber is received the solder paste.

2. The head of claim 1 which comprises: a second squeegee blade, the blade having an edge and ends, the blade fixedly secured to the coupling block and in an orientation which is the mirror image of the first squeegee blade means for applying pressure to said second squeegee blade wherein when the first blade is in its print stroke position and move through a print stroke, the second blade contacts but does not bind to the foil.

3. The head of claim 2 wherein the squeegee blades define an angle of approximately 60° with the stencil foil surface.

4. The head of claim 2 or 3 wherein the means for flexibly closing the ends of the squeegee blades comprises a pair of retaining walls moveably secured to the coupling block, the walls having bottom edges which are biased to engagement with the stencil surface, and the retaining walls engage the edges of the squeegee blades.

5. The head of claim 4 wherein the retaining walls are spring loaded and secured to the coupling block.

6. The head of claim 5 wherein leaf springs are secured to the end blocks of the coupling bloc; the retaining walls each comprise an upper edge which engages the leaf spring; and each retaining wall is characterized by at least one slot and slidably secured to the coupling block, the slots defining the travel of the retaining walls.

7. The head of claim 2 wherein the means for applying pressure comprises a pressure bar having at least two bearing surfaces, a horizontal bearing surface to engage the coupling bar and control the pressure on the associated squeegee edge and a vertical bearing surface engaging the coupling block to drive the head through a print stroke.