JP2010245560A - Support with solder powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a support with solder powder used for precoating that achieves uniform coating, causes no defect, and is implemented by simple facilities since conventional precoating methods such as a plating method, a hot leveler method, a solder paste method, and a solder ball method have problems that sticking of solder on a soldering part is not uniform, solder does not stick completely, and large facilities and labor are needed. <P>SOLUTION: Powdery solder which is more than needed is scattered over an adhesive applied to a support and then excessive powdery solder which is not sticking on the adhesive is removed. Then the powdery solder scattered surface is put over a work coated with flux by applying pressure, and then heated to make the solder stick on the soldering part. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a support with solder powder used in a solder pre-coating method in which solder is attached in advance to a soldered portion of a workpiece for electronic equipment.

  Generally, in order to solder a work for electronic equipment such as a printed circuit board, a chip part, a wafer element, an integrated circuit part such as a BGA, and a CSP (hereinafter simply referred to as a work), the molten solder jetting the soldering part is used. There are a flow method of contacting and a reflow method of applying a solder paste to a soldering part of a work and then heating the work with a heating device such as a reflow furnace.

  In the flow method, a liquid flux is applied to a printed circuit board on which electronic components are mounted, and the flux is dried and then brought into contact with molten solder that is jetted to perform soldering. However, in this flow method, when the soldering portion is very small, not only the molten solder is difficult to adhere, but also the amount of adhesion varies even if the solder adheres, and there is a problem in reliability thereafter. Moreover, the flow method requires large-scale equipment such as a fluxer for applying flux to the work, a preheater for drying and preheating the flux, and a solder bath for melting and jetting solder.

  In the reflow method, a mask with holes formed at positions corresponding to the soldered portions of the printed circuit board is placed on the printed circuit board, a solder paste is further placed on the mask, and the solder paste is scraped with a squeegee. As a result, the solder paste is filled in the holes of the mask. Then, the mask is removed and a solder paste is applied to the soldering portion. This is heated by a heating device such as a reflow furnace, and soldering is performed by melting the solder paste. With this reflow method, it is possible to attach solder even to a soldering portion that is small to some extent, but there is still variation in the amount of adhesion. In the reflow method, it is necessary to prepare a mask according to the workpiece. When the workpiece is very small, it takes a lot of labor to match the hole of the mask with the soldered portion of the workpiece. In addition, in the reflow method, an apparatus for printing and applying the solder paste is necessarily required, and this apparatus is not only expensive but also needs to secure an installation location.

  In view of the problems of the flow method and the reflow method, recently, “solder pre-coating” in which solder is previously attached to a soldering portion of a workpiece has been adopted. As a method for obtaining the solder precoat, there are a plating method (Patent Document 1), a hot leveler method (Patent Document 2), a solder paste method (Patent Document 3), a solder ball method (Patent Document 4), and the like.

Japanese Patent Laid-Open No. 9-167883 Japanese Patent Laid-Open No. 11-54890 Japanese Patent Laid-Open No. 8-3007047 JP-A-8-340174

  By the way, the plating method for obtaining the solder precoat is to immerse the workpiece in a plating solution and deposit the solder on the soldered portion of the workpiece. There was something. That is, in the plating method, since the type of the plating solution is limited, a solder having a desired composition cannot be precoated. In addition, since the plating method requires a large amount of equipment for the treatment of the plating solution, there is also a problem that the initial cost becomes expensive. Furthermore, in the plating method, it is difficult to attach a necessary amount of solder, that is, an amount of solder that can be soldered, to the soldering portion of the workpiece.

  In the hot air leveler method, when a work is immersed in molten solder and taken out from the molten solder, hot air is blown to the work to blow off excess solder. Although this hot air method can adjust the amount of solder adhesion by adjusting the hot air, there is a problem that the amount of solder adhesion varies greatly.

  Similar to the reflow method, the solder paste method uses a mask in which a hole is formed at a position corresponding to the soldered portion, and after aligning the soldered portion of the workpiece with the hole of the mask, the solder paste is applied onto the mask. Then, the workpiece is heated after removing the mask, thereby melting the solder paste and attaching the solder to the soldering portion of the workpiece. By the way, in the solder paste method, when the soldered portion of the workpiece becomes minute, it becomes very difficult to match the soldered portion and the mask hole, and the solder paste is often not applied to the soldered portion. Further, the solder paste method has a problem that the solder paste is filled into the minute holes of the mask and the solder paste after filling is not applied to the soldered portion.

  In the solder ball method, a solder pre-coat is obtained by adsorbing a solder ball with an adsorption jig, mounting it on the soldering part of the workpiece, and then heating the workpiece with a heating device such as a reflow furnace to melt the solder ball. It is. In this solder ball method, if a solder ball of a certain size is available, the amount of solder adhesion can be made uniform. However, this solder ball method has a limited shape that can form only a circular precoat like a solder bump. there were. In addition, the solder ball method requires a solder ball of a predetermined size to be prepared in advance. However, the manufacture of this solder ball requires a lot of labor and equipment, and is expensive. . In addition, the solder ball method uses a suction jig to pick up the solder ball, then blows air out of the suction hole and releases the solder ball to mount the solder ball on the soldered part of the workpiece. When the solder balls are attracted, multiple solder balls are attracted to one hole due to static electricity, or when the solder balls are released on the workpiece, the solder balls are blown off by the force of air ejected from the attracting holes. There has been a problem that solder balls are not mounted on the soldering part of the workpiece.

  The present invention was invented in view of the problems of the conventional pre-coating method. The solder can be uniformly applied not only to a small soldering part but also to a large soldering part, and no expensive equipment is required. An object of the present invention is to provide a support with solder powder used in a solder pre-coating method in which even a solder having a composition can be attached.

  When the present inventors sprayed a powdery material on a sticky surface, only the bottommost layer of the powdery material adheres to the adhesive, and when the powdered solder is in contact with the soldering part, the molten solder Moved from the pressure-sensitive adhesive to the soldering part and adhered, but when there was no soldering part in the vicinity of the molten solder, it was found that the molten solder was difficult to move, and the present invention was completed.

The present invention is as follows.
(1) After the flux is applied to the entire surface of the workpiece, the powder solder attached to the adhesive of the support and the soldered portion of the workpiece are overlapped and then crimped, and the powder solder is in a position that matches the soldered portion. Acrylic pressure-sensitive adhesive is applied on a support selected from aluminum, stainless steel, polyimide resin, plastics, and glass epoxy resin composite. Then, a support with solder powder in which powder solder is sprayed without gaps and only one layer of the powder solder is adhered to the adhesive surface of the support.

(2) The support body with solder powder as described in (1) above, wherein the powder solder is a powder solder having a lower limit of 5 μm and an upper limit of 15 μm.
(3) The support with solder powder according to (1) or (2) above, wherein the pressure-sensitive adhesive is a pressure-sensitive adhesive that exhibits adhesiveness at room temperature or a temperature equal to or higher than room temperature.

  (4) The support with solder powder according to any one of the above (1) to (3), wherein the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive has a thickness of 1 μm or more and less than 50 μm.

  According to the present invention, it is excellent in the reliability that the solder is surely adhered to the soldered portion of the workpiece, and there is no defect like unsolder even if the workpiece is minute, and soldering of any composition is possible. In addition, there is no need to prepare a jig corresponding to the soldering part of the workpiece, such as a mask used in the printing method or a suction jig used in the solder ball method. is doing. And since the fixed amount solder has adhered uniformly to the soldering part, when the workpiece | work and the other workpiece | work are soldered, the workpiece | work for electronic devices of this invention becomes firm joining.

Adhesive application process on support The process of spraying powder solder on the adhesive Process for removing excess powder solder Process of applying flux to workpiece Process of stacking support and workpiece Heating the support and workpiece The process of removing the support after solidification of the solder Process to remove unnecessary solder

DESCRIPTION OF SYMBOLS 1 Support body 2 Adhesive 3 Powder solder 5 Work 6 Soldering part 8 Flux 9 Resist

  For the support used in the present invention, a material having heat resistance that maintains its shape even when heated above the melting point of the powder solder and that is difficult to adhere molten solder is suitable. Supports suitable for use in the present invention are metals such as aluminum and stainless steel, plastics such as polyimide resin and glass epoxy composite, and composites.

  The pressure-sensitive adhesive to be applied to the support basically serves to adhere and fix the powder solder further, and adheres the powder solder to the soldered part following the unevenness of the member surface during thermocompression bonding. The pressure-sensitive adhesive used in the present invention can be selected from a pressure-sensitive adhesive having an adhesive strength at room temperature and a hot-melt pressure-sensitive adhesive that exhibits a pressure-sensitive adhesive force by heating. The thickness of the adhesive layer is advantageously about 1 μm or more and less than 50 μm, but is not particularly limited to this thickness.

  In the present invention, the powder solder that is not adhered to the adhesive is removed after the powder solder is spread on the adhesive applied to the support without any gaps. Equalize, blow off with weak compressed air, or turn the support upside down to lightly vibrate. At this time, care must be taken not to remove even one layer of powder solder adhering to the adhesive.

  The powder solder used in the present invention is selected depending on the desired solder film thickness. That is, a fine powder is selected when a thin solder film is desired, and a large powder is selected when a thick solder film is desired. From the economical viewpoint, it is desirable to classify and use powder solder obtained by an atomizing method or the like by economical selection.

  It is desirable that the flux used in the present invention is present in a necessary amount in the soldered portion of the workpiece and is reduced as much as possible in a non-soldered portion such as a resist surface. In general, the soldering part of the workpiece is lower than the top surface of the resist. After flux is applied to the entire surface of the work, if the flux on the resist surface is scraped off to the soldering part with something like a rubber blade, the soldering part Since the flux is always applied to the solder, the molten solder is smoothly joined to the soldered portion, and the molten solder is stagnated in the resist portion, and no bridge is generated in the high-definition soldered portion.

  In the present invention, the flux is applied to the soldering surface of the workpiece, and then the workpiece and the support to which the powder solder is adhered are superposed and then crimped. The pressing force at this time varies depending on the surface shape of the workpiece, the workpiece area, and the pressure bonding accuracy, but is preferably 1 Newton or more per square centimeter. Further, the heating temperature when heating the workpiece and the support superimposed on each other is preferably equal to or higher than the melting point of the powder solder.

  When the support is removed by cooling immediately after the powder is melted, solder is formed on the soldering portion of the workpiece. However, surplus solder exists on the resist surface other than the soldered portion, and the solder is removed as it becomes a bridge between the soldered portions and the insulation resistance is lowered. Any method may be used to remove the excess solder, but removal by washing is suitable. When the cleaning is performed here, the flux residue present in the soldering portion can be removed at the same time, so that the reliability is further improved. And if the shape of the solder adhering to a soldering part is further prepared, after applying a flux to a soldering part again, you may add the process of heating and cooling more than the melting temperature of solder.

  In the present invention, the accuracy of the solder film thickness attached to the soldering portion is high. The reason is that the amount of the powder solder that adheres to the adhesive surface of the support has little variation per unit area. Therefore, when the pressure is applied with the support and workpiece superposed, the powder solder comes into contact with the soldered part, so even when the powder solder is melted, the molten solder is always in contact with the soldered part. A certain amount of powder solder on the soldering part adheres, and the film thickness accuracy is improved. Solder powder in contact with the resist surface other than the soldering portion is also melted, but lateral wetting and spreading are suppressed by the adhesive layer that does not wet with the solder. As a result, it is difficult for a bridge to be generated even with respect to a high-definition soldering pattern.

Hereinafter, the precoat method of the present invention will be described with reference to the drawings. 1 (A) to 8 (H) are explanatory views of a process for performing pre-coating of the present invention.
A. Adhesive application step on the support;
An adhesive 2 is applied to one side of the support 1.

B. The process of spraying powder solder on the adhesive;
Powder solder 3... Is spread on the pressure-sensitive adhesive 2 applied to the support 1 so that the pressure-sensitive adhesive 2 is hidden.

C. removing excess powder solder;
The powder solder on the support 1 is leveled with a brush 4 to remove excess powder solder 3... Not adhered to the adhesive 2.

D. The process of applying flux to the workpiece;
A liquid flux 8 is applied by a spray fluxer 7 to the surface of the workpiece 5 on which the soldering portions 6. Thereafter, the flux applied to the non-soldering portion such as the resist 9 other than the soldering portion may be removed as necessary.

E. The process of stacking the support and workpiece;
The flux application surface of the workpiece 5 and the powder solder adhesive surface of the support 1 are overlapped. At this time, pressure is applied between the workpiece 5 and the support 1 from above the support 1 with a press machine (not shown). Then, since the adhesive has followability, when pressure is applied to the support 1, the solder powder 3... Adhered to the adhesive 2 is a soldered portion at a position slightly recessed from the resist 9 of the workpiece 5. 6 will come into contact.

F. heating the support and the workpiece;
The superposed workpiece 5 and the support 1 are heated by a heating device (not shown) to melt the powder solder 3... Adhered to the adhesive 2 of the support 1. At this time, the powder solder that has been in contact with the soldering portion 6 of the workpiece 5 is melted and spreads to the soldering portion 6, but the powder solder that has been on the resist 9 remains in place even if it melts.

G. Step of removing the support after the solder is solidified;
If the molten solder adheres to the soldering portion 6 of the workpiece 2, the workpiece 2 and the support 1 are cooled to solidify the molten solder, and the precoat 10 is formed on the soldering portion 6. Thereafter, the support 1 is removed (arrow).

H. The process of removing the solder of unnecessary parts;
If the solder remains on an unnecessary portion such as the resist 9, it causes a reduction in bridge and insulation resistance as described above, so the solder at the unnecessary portion is removed. Since the solder at the unnecessary portion is fixed with the flux residue, the solder is immersed in a cleaning solution 11 that can dissolve the flux residue and cleaned. Hot water is suitable when a water-soluble flux is used, and an organic solvent such as alcohol is suitable when a resin-based flux is used. Further, in order to adjust the shape attached to the soldering portion, reheating / cooling may be performed after applying a flux to the soldering surface.

Next, solder was attached to the workpiece by the pre-coating method as follows.
A 200 μm thick aluminum was used as a support, and a 10 μm thick acrylic adhesive layer was formed on one side. Sn-3Ag-0.5Cu powder solder obtained by the atomization method was classified with a lower limit of 5 μm and an upper limit of 15 μm, and adhered to the adhesive surface of the support. At this time, the powder solder was sufficiently dispersed so that the adhesive was hidden. Next, the powder solder spread on the support was scraped with a brush, and then weaker compressed air was blown to remove excess powder solder. When the spray surface after removing this excess powder solder was observed with a microscope, only one layer of powder solder adhered to the adhesive. The workpiece for forming the solder precoat is a 30 × 30 mm glass epoxy substrate having an outer shape. The glass epoxy substrate has 3600 electrodes to be soldered at a pitch of 200 μm, and the resist near the electrode has a thickness of 25 μm. A liquid water-soluble flux was applied on the surface of the workpiece having the electrode, and the flux applied on the resist was scraped off with a rubber blade to sufficiently fill the electrode portion with the flux. Only a very thin flux remained on the resist portion scraped off with the rubber blade. After superposing the powder solder part of the support and the flux application surface of the workpiece, a pressure of 100 N was applied on the support with a press machine, followed by heating at 220 ° C. for 10 seconds and then cooling. The support was removed from the cooled workpiece, and the workpiece was washed with 40 ° C. warm water to remove the solder adhering to the resist. Furthermore, in order to adjust the shape of the solder adhered to the soldering portion, a flux was applied to the soldering portion, heated again to a temperature higher than the melting temperature of the solder, cooled, and then washed with warm water. As a result, a solder precoat of 30 μm ± 3 μm was formed only on the electrode portion of the workpiece.

  The present invention provides not only a relatively large electronic component such as a printed circuit board but also a solder film thickness accuracy on a wiring portion or an electrode portion such as a wafer or CSP having a minute soldering portion such that an electrode has a diameter of 0.2 mm or less. High-definition solder precoat can be formed.

Claims (4)

  After flux is applied to the entire surface of the workpiece, the powder solder adhered to the adhesive of the support and the soldered part of the workpiece are overlaid and then crimped, and only the powder solder that matches the soldered part is attached to the workpiece. A support used in a method of heating and press-bonding to a soldering portion of an aluminum, stainless steel, polyimide resin, plastics, a glass-epoxy resin composite, a support material selected from an acrylic adhesive and powder A support body with solder powder in which solder is dispersed without any gap and only one layer of powder solder is adhered to the adhesive surface of the support body.   2. The support with solder powder according to claim 1, wherein the powder solder is powder solder having a lower limit of 5 μm and an upper limit of 15 μm.   The support with solder powder according to claim 1 or 2, wherein the pressure-sensitive adhesive is a pressure-sensitive adhesive that exhibits adhesiveness at room temperature or a temperature equal to or higher than room temperature.   The support body with solder powder according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive has a thickness of 1 µm or more and less than 50 µm.

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