Solder precoating method and workpiece for electronic equipment

Abstract

Problem Precoating methods for previously adhering solder to areas to be soldered of a workpiece for an electronic part such as a printed circuit board, a chip part, or a wafer include the plating method, the hot leveling method, the solder paste method, the solder ball method, and the like. In these conventional precoating methods, solder did not uniformly adhere to areas to be soldered, solder did not completely adhere, and much equipment and time were required. The present invention provides a method which can perform precoating with uniform application and without the occurrence of defects using simple equipment and a workpiece to which solder is uniformly adhered. Means for Solving the Problem In the present invention, an excess amount of solder powder is dispersed atop an adhesive applied to a substrate, and then excess solder powder which is not adhered to the adhesive is removed. The surface on with solder powder is dispersed is then stacked on a workpiece to which flux is applied with the application of pressure, heating is then performed, and solder is adhered only to areas to be soldered.

Claims

1. A solder precoating method comprising: applying an adhesive atop a substrate; dispersing a solder powder atop the adhesive in an amount greater than an amount necessary to completely cover the adhesive and adhering a single layer of solder powder to the adhesive; removing from the substrate excess solder powder not in the single layer; coating a surface to be soldered of a workpiece with flux; stacking the surface of the substrate to which solder powder is adhered and the flux-coated surface of the workpiece and applying pressure; heating the stacked substrate and workpiece to adhere the solder powder to areas to be soldered of the workpiece; removing the substrate from the workpiece while leaving solder adhered to the areas to be soldered of the workpiece; and removing adhered solder from locations on the workpiece other than the areas to be soldered of the workpiece.

2. A solder precoating method as claimed in claim 1 wherein the adhesive exhibits adhesion at or above room temperature.

3. A solder precoating method as claimed in claim 1 wherein the substrate is selected from materials having heat resistance at the melting point of the solder or higher.

4. A solder precoating method as claimed in claim 1 wherein the substrate is selected from metals, ceramics, and plastics.

5. A solder precoating method as claimed in claim 1 including heating the stacked substrate and workpiece to melt adjoining solder powder together and form layers of molten solder adhered to the areas to be soldered of the workpiece.

6. A solder precoating method as claimed in claim 1 wherein the workpiece includes a resist having a top surface higher than a top surface of the areas to be soldered, and the amount of solder adhered to each area to be soldered is such that a top surface of the adhered solder extends above the top surface of the resist.

7. A solder precoating method as claimed in claim 1 wherein the workpiece includes a resist between the areas to be soldered, and heating the stacked substrate and workpiece melts solder powder opposing the resist.

8. A solder precoating method as claimed in claim 7 including melting together adjoining solder powder opposing the resist to form layers of molten solder opposing the resist.

9. A solder precoating method as claimed in claim 1 wherein the areas to be soldered comprise electrodes of the workpiece.

10. A solder precoating method as claimed in claim 1 wherein the adhesive is an acrylic adhesive.

11. A solder precoating method comprising: applying an adhesive atop a substrate; dispersing a solder powder atop the adhesive in an amount greater than an amount necessary to completely cover the adhesive and adhering a single layer of solder powder to the adhesive; removing from the substrate excess solder powder not in the single layer; placing the substrate and a workpiece having electrodes formed on a surface thereof in a stacked relationship with the solder powder on the substrate opposing the surface of the workpiece on which the electrodes are formed; heating the stacked substrate and workpiece to at least the melting temperature of the solder powder while applying pressure to melt adjoining solder powder together and form a layer of molten solder adhered to each electrode of the workpiece; cooling the workpiece to solidify the molten solder and then removing the substrate from the workpiece; and removing adhered solder from locations on the workpiece other than the electrodes.

12. A solder precoating method as claimed in claim 11 wherein the workpiece includes a resist which separates the electrodes from each other, the substrate and the workpiece are placed in the stacked relationship with the solder powder on the substrate opposing the resist on the workpiece, and the heating melts together adjoining solder powder opposing the resist to form layers of molten solder opposing the resist.

13. A solder precoating method as claimed in claim 12 wherein cooling the workpiece solidifies the molten solder on the electrodes and the molten solder on the resist, and removing the substrate from the workpiece leaves solidified solder on the electrodes and the resist.

14. A solder precoating method as claimed in claim 11 wherein the adhesive is an acrylic adhesive.

15. A solder precoating method as claimed in claim 11 including removing the excess solder powder with a brush.

16. A solder precoating method as claimed in claim 11 including removing the excess solder powder with compressed air.

17. A solder precoating method as claimed in claim 11 including dispersing the solder powder atop the adhesive in an amount sufficient to hide the adhesive beneath the solder powder.

Description

BRIEF EXPLANATION OF THE DRAWINGS

(1) FIG. 1—Step of applying an adhesive to atop a substrate

(2) FIG. 2—Step of dispersing solder powder atop the adhesive

(3) FIG. 3—Step of removing excess solder powder

(4) FIG. 4—Step of applying flux to a workpiece

(5) FIG. 5—Step of stacking the substrate and the workpiece

(6) FIG. 6—Step of heating the substrate and the workpiece

(7) FIG. 7—Step of removing the substrate after solidifying the solder

(8) FIG. 8—Step of removing solder from unnecessary locations

EXPLANATION OF SYMBOLS

(9) 1 substrate 2 adhesive 3 solder powder 5 workpiece 6 areas to be soldered 8 flux 9 resist

INDUSTRIAL APPLICABILITY

(10) The present invention can form fine solder precoats having a highly accurate film thickness on wiring or electrodes not only of relatively large electronic parts such as printed circuit boards but also on wafers, CSP's, and the like having very small areas to be soldered, such as electrodes with a diameter of at most 0.2 mm.