Printing – Stenciling – Processes
Reexamination Certificate
2000-07-24
2003-10-21
Evanisko, Leslie J. (Department: 2854)
Printing
Stenciling
Processes
C101S485000, C101S114000, C101S126000, C101S425000
Reexamination Certificate
active
06634290
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a mask-printing method and a mask-printing apparatus and particularly to the art of dealing with a defective printing.
2. Related Art Statement
A mask printing is carried out for, e.g., printing a creamed solder on a printed wiring board (“PWB”). More specifically described, a mask having one or more through-holes is superposed on the PWB, and the creamed solder is moved on the mask and is squeezed into the through-holes of the mask, so that the creamed solder is applied to the PWB. However, a defective mask printing may occur. A defective mask printing may be a printing with an insufficient amount of creamed solder, or a printing at an incorrect position on the PWB. To deal with this problem, Japanese Patent Application laid open under Publication No. 5-50578 teaches inspecting whether a creamed solder has been appropriately printed on a PWB and, if a defective printing is found, solving the cause of the defective printing to prevent the same defective printing from repeating two or more times.
Thus, the prior-art document teaches solving the cause of the defective printing. However, the PWB with the defective printing is dealt with as a defective object, and is discarded out of a production line.
SUMMARY OF INVENTION
The present invention provides a mask-printing method and a mask-printing apparatus which have one or more of the following technical features that are described in below in respective paragraphs given parenthesized sequential numbers (1) to (19). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, but not all) of those items.
(1) According to a first feature of the present invention, there is provided a method of printing a printing material on an object, comprising the steps of printing the printing material on the object through a mask having at least one through-hole formed through a thickness thereof; inspecting the printing material printed on at least one portion of the object through the at least one through-hole of the mask; and re-printing, when the inspection shows that an amount of the printing material printed on the at least one portion of the object is short, the printing material on the at least one portion of the object through the at least one through-hole of the mask to compensate for the short amount of the printing material.
The printing material may be a creamed solder or an adhesive. The object may be a printed wiring board (“PWB”), or an externally exposed substrate of a “leadless” electric component having no lead wires. The leadless electric component is a package electric component which is provided by a container and chip components held by the container. The mask may be a screen mask formed of fibers, a combination mask obtained by reinforcing a screen mask with metal, or a stencil mask formed of metal. The shortage of the amount of the printing material may be compensated, according to the second feature (2) described below, by carrying out the mask-printing operation once more over the entire portion of the object. In an alternative manner, the mask is not used, and a device which can print the printing material on only a d&sired portion of the object is employed, so that the printing material is printed on only one or more print spots where the shortage of printing-material amount has been found. The inspection may be carried out on all the print spots of the object where the printing material has been printed, or on only a portion (one, two, . . ., but not all) of the print spots. In the latter case, the inspection may be carried out on a particular portion of the print spots where the shortage of printing-material amount is likely to occur, or a portion of the print spots that is random-sampled for each of objects. The re-printing can compensate for the short amount of printing material, and the object on which the shortage of printing-material amount has occurred need not be discarded as a defective. Thus, in the case where the object is a PWB and the printing of the printing material is carried out as one step of a printed-circuit board producing method, the number of PWBs that are discarded from the production line can be largely reduced.
(2) According to a second feature of the present invention that includes the first feature (1), the printing step comprises printing the printing material on a plurality of portions of the objects through the mask having a plurality of through-holes formed through the thickness thereof, the inspecting step comprises inspecting the printing material printed on at least one of the plurality of portions of the object through at least a corresponding one of the plurality of through-holes of the mask, and the re-printing step comprises re-printing, when the inspection shows that an amount of the printing material printed on the at least one portion of the object is short, the printing material on each of the plurality of portions of the object through a corresponding one of the plurality of through-holes of the mask.
The re-printing step may be the same step as the printing step and accordingly may be easily carried out by repeating the printing step.
(3) According to a third feature of the present invention that includes the second feature (2), the re-printing step comprises re-printing the printing material on the each portion of the object through the corresponding one through-hole of the mask, such that an amount of the printing material squeezed into the one through-hole in the re-printing step is smaller than the amount of the printing material squeezed into the one through-hole in the printing step.
This feature may be achieved by, e.g., decreasing the pressure under which the printing material is squeezed into the through-hole, or the time duration during which the printing material is squeezed into the through-hole. Since some amount of the printing material is, though being short, already present on the object, a total amount of the printing material printed on the object would be excessive if the same amount of printing material as that printed in the printing step is printed in the re-printing step. However, this feature is free of the problem that an excessive amount of printing material is printed on an object.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the inspecting step comprises taking, with an image taking device, an image of a surface of the object on which the printing material has been printed, and finding, based on the taken image, the shortage of the amount of the printing material.
The shortage of the printing material printed on the object can occur in various manners. For example, the height of the printing material is insufficient, or the printing material has a chip, i.e., no printing material is printed on at least a portion of a print area on which the material should be printed. The image taking device may be provided by a two-dimensional-image taking device which is used in combination with a planar-light source; or a laser displacement sensor disclosed in the above-identified Japanese Patent document No. 5-50578. The laser displacement sensor includes a laser-beam generator, an optical system, and a reflected-light converging device, emits a laser beam toward the printing material, and takes an image of the printing material based o
Adachi Jun
Mizuno Manabu
Shimizu Toshinori
Evanisko Leslie J.
Fuji Machine Mfg. Co. Ltd.
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