Printing – Stenciling – Traveling-inker machines
Reexamination Certificate
2001-03-07
2004-04-27
Yan, Ren (Department: 2854)
Printing
Stenciling
Traveling-inker machines
C118S413000
Reexamination Certificate
active
06725769
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for applying a viscous or paste-like material through apertures in a stencil onto a substrate beneath the stencil and is particularly suitable for applying solder paste onto a board for producing a printed circuit board or for applying an adhesive or other bonding agent to a substrate via a stencil.
Control of the flow characteristics and composition of materials and the pressure thereof in the stencil printing onto substrates is very important if good results are to be achieved.
Difficulty has been hitherto experienced in balancing or controlling the higher pressure required for displacing solder paste from a reservoir to dispensing pressure relative to the lower pressure required for deposition at the actual stencil surface and it is with the resolution of such difficulties with which our aspect of the present invention is concerned.
With solder paste material and other materials which may contain volatile components it is important to confine the material within a relatively closed space to prevent evaporation and where the materials are thioxotropic or contain such additives, it is important to minimise any evaporation. It has now also been discovered desirable and advantageous to maintain a movement of the viscous or paste-like material, especially immediately prior to application so as to maintain relatively constant rheological characteristics of the soldering paste and it is with this object with which a first aspect of the present invention is concerned.
Recent attempts have been made to provide improved apparatus for application of solder paste such as in WO/96/20088 of Ford Motor Co. Ltd. (PCT/GB95/03002) wherein a compression head cap provides a contained environment to direct and to aid the flow of pressurised viscous material through openings (
48
) in the stencil. The compression head cap (
8
) includes two generally parallel wiper blades (
78
′,
78
) acting on the stencil with their end edges only that are in sliding communication with the stencil (
46
). Longitudinal diffusion plates (
90
) guide and equalise flow of the viscous material into the volume between the two generally parallel and upwardly extending wiper blades (
78
′,
178
) acting on the stencil with their end edges only. In this apparatus the viscous material is forced through the interior chamber (
66
) of the compression head (
6
) wherein it is diffused by a diffuser (
90
) with the material then flowing into the exit (
68
), and then on to the stencil surface. EP-A-0504501 Zimmer and U.S. Pat. No. 4,023,486 also disclose some of these features of Ford.
In WO 98/16387 Societe Novatec S. A. (PCT/EP97/05761) the apparatus of the Ford disclosure is described as not overcoming realised problems and possessing various disadvantages. Specification WO 98/16387 of Novatec discloses a hollow receptacle (
7
) in which a piston (
10
) is displaceable to urge soldering paste (
9
) through apertures in a grill (
17
) functioning as a homogenising element upstream of two inclined wiper members (
15
,
16
) and then between the upper members (
15
,
16
) and onto the stencil and through the apertures in the stencil. In this device there are no means within the hollow receptacle (
7
) above the grill (
17
) for creating a flow of paste material other than through the grill and, furthermore, a considerable amount of paste may remain in the space defined beneath the grill and partially encompassed by the wiper blades—which may lead to a reduction in quality of paste or other material when the device is temporarily out of use. DE offenlegungschrift 2250092 discloses a similar arrangement to Novatec.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided apparatus for use in a stencil printing machine which has a carriage for executing reciprocable movements or strokes, for applying a viscous or paste fluid material to the surface of a stencil and through apertures therein onto a substrate, said apparatus comprises a fluid material applicator device which is slideable along an upper surface of a stencil and has at least one aperture in the lowermost surface through which may flow the fluid material to be deposited on the substrate below, at least one fluid material reservoir or means for receiving such in fluid material flow-communication with a flow passage in said applicator device, and means operable for displacing the fluid material during each stroke of the stencil printing machine of an amount greater than necessary to supply fluid material to the at least one outlet aperture for deposition on the substrate via the stencil.
The greater amount of fluid material which is displaced in the applicator device often requires a significantly greater pressure than desirable for application of fluid material to the stencil, and it has been found desirable for a pressure reduction means, such as a partition with one or more apertures or other flow restriction means, to be provided prior to said at least one outlet and preferably between a main flow passage of the applicator device or head and a passage leading to such outlet. A significant reduction of pressure is often required, such as in the order of a ratio of 6 to 1, for example, in a reduction of say 30 p.s.i. to 5 p.s.i.
In a second aspect according to the present invention there is provided apparatus for use in a stencil printing machine and for applying a viscous or paste-like material or other fluid material through apertures in a stencil and onto a substrate beneath the stencil, comprising a fluid material applicator device which is slideable along an upper surface of a stencil in fluid retaining relationship therewith and has a main-flow passage in which fluid material may flow in alternate directions or through which fluid material may flow in alternate directions or in reciprocable manner or may flow intermittently interruptably or continuously in the same direction and also communicates with at least one aperture in the lowermost surface through which may flow the fluid material to be deposited on the substrate, and at least one fluid material reservoir or means for receiving such in fluid material ducting flow-communication with said main-flow passage, and means for exerting pressure on said fluid material alternatively from either end of said main flow passage preferably after each stroke of the printing machine, or means for exerting pressure intermittently or continuously in the same direction, with means preferably provided or available for accommodating the flow of fluid material resulting from said pressure application which is additional to the flow of material required for a deposition on the substrate.
Preferably two reservoirs will be provided one at either end of said main flow passage and preferably comprise two cartridges as piston cylinder arrangements and with the pistons alternately displaceable during each stroke of the stencil printing machine so as to drive fluid material in opposite directions, even if only for two or three millimeters, for example, to keep the level of the fluid moving during printing.
Preferably the lowermost surface of the applicator device is planar or substantially planar and the device is such as to enable the two pressure members of the printing machine, in use when the applicator device is located thereunder, to be urgeable against receiving means on the upwardly facing side of the device, so that the planar lower surface is urgeable against the upper surface of the stencil on which it is sliding and the pressure members alternate in application to be on the downstream side of the device with respect to the direction of displacement of the device and above the sealing edge of the at least one lowermost aperture.
In one embodiment, an elongate slot as said at least one aperture is provided for the passage of paste or other fluid although such may be multi-apertured such as in the form of a grill or mesh or the like, and preferably the sheet of material defining such will be integral an
Dek International GmbH
Dennison Schultz Dougherty & MacDonald
Yan Ren
LandOfFree
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