JP2005229029A - Method of soldering and solder cream used for the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for improving the yield, by reducing the proportion of the defects in soldering, and to provide solder cream for realizing the method thereof. <P>SOLUTION: The method to be disclosed includes a step of applying a solder cream 3 containing a plurality of grains 5 of specific gravity smaller than the solder to a substrate 1, a step of arranging units 4 at predetermined positions on the substrate 1 on which the solder cream 3 is applied, a step of melting the solder cream 3 by heating the substrate 1 on which the units 4 are arranged, and a step of cooling the substrate 1 on which the units 4 are arranged. In the step of melting, the solder is made to adhere to the parts to be soldered of the units 4, which are separated by gaps from the liquid surface of the solder through heating, by the floating of a plurality of the grains 5 on the liquid surface of the solder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of soldering each unit to a substrate and a solder cream used in the method, and more specifically, using a solder cream including a plurality of particles having a specific gravity smaller than that of solder, and by melting the solder cream, The present invention relates to a soldering method characterized in that particles float on a solder liquid surface, and solder is attached to a joint portion separated from the solder liquid surface of a unit, and a solder cream used in the method.

  An electronic component is manufactured by placing each unit, which is a standardized component such as a semiconductor device, on a printed circuit board and soldering. Soldering is, for example, reflow, that is, applying solder cream (a paste with flux added to the solder powder) on the substrate, placing each unit in place, heating the solder cream, and then cooling (See, for example, Patent Document 1, Patent Document 2, and Patent Document 3). Lead-tin solder can be used as solder cream, but lead is known as a substance that causes neurological damage when accumulated in the body, and it contains lead under the influence of acid rain. It is pointed out that lead may be melted out of objects, and lead-free solder is often used because of these problems. As lead-free solder, tin-silver-copper solder, tin-nickel-copper solder, tin-silver-bismuth-copper solder, tin-silver-indium-bismuth solder, tin-silver solder, tin-antimony solder, etc. are used Has been.

  When soldering by the above-described method, the solder cream is melted and soldered by heating to about 200 ° C. to about 300 ° C., and the package is made thin by miniaturization and thinning of parts. Each of the units thus produced is prone to deformation such as warpage due mainly to the difference in thermal expansion between the substrate and the unit, and many units that do not satisfy the standards that can be shipped as products are manufactured. While the deformation such as the warp is slightly corrected in the cooling step performed to solidify the solder by reducing the difference in thermal expansion, in the correction, the unit is adjacent to the solder applied to the substrate. It does not lead to. In general, in the case of a high-density mounting substrate, the units are densely packed, and it is difficult to replace the unit after the soldering process is completed, and not only the unit but also the printed circuit board itself is a defective product. As a result, there is a problem that the yield is deteriorated.

  In addition, the electronic component must be within a range in which the height difference of each unit is 0.1 mm or less according to the standard. Many of the above-mentioned methods that become defective products cause deformation such as warpage, and the above-mentioned height difference becomes about 0.15 mm, so long as deformation such as warpage of about 0.05 mm can be suppressed or corrected. Can be adopted as a product. Therefore, a method capable of suppressing or correcting the deformation such as the warp of about 0.05 mm is desired.

JP 10-70359 A Japanese Patent Laid-Open No. 9-115575 JP-A-8-250847

  In view of the above-described problems, an object of the present invention is to provide a method for reducing the ratio of defective products in soldering and improving yield and a solder cream for realizing the method.

  In the present invention, by including particles having a specific gravity smaller than that of solder in the solder cream, the particles float on the solder liquid surface due to melting of the solder, exposed from the liquid surface, and are deformed such as warp by heating. Deformation such as warping is corrected by attaching solder to the joint part of the unit and cooling it, and the attached solder is adjacent to the solder liquid surface or particles that are partially exposed from the solder liquid surface Thus, it was made by finding that deformation such as warpage is corrected by solidification and shrinkage of the solder. The above objects are achieved by providing the method of the present invention and a solder cream for realizing the method.

That is, according to the invention of claim 1 of the present invention, a method of soldering each unit on a substrate,
Applying a solder cream containing particles having a specific gravity smaller than that of solder on the substrate;
Arranging each unit at a predetermined position on the substrate to which the solder cream is applied;
Heating the substrate on which the units are arranged to melt the solder cream;
Cooling the substrate on which the units are arranged,
In the melting step, a method is provided in which the plurality of particles float on the solder liquid surface, so that solder is attached to the joint portion of the unit separated from the liquid surface by the heating.

  According to the second aspect of the present invention, there is provided a method in which the particles are produced from magnesium, aluminum, titanium or an alloy thereof, silicon, silicon dioxide, silicon nitride, fluororesin, polyphenylene sulfide resin, and polyamide. The

  According to a third aspect of the present invention, the particles include the magnesium, the aluminum, the titanium, or an alloy thereof, the silicon, the silicon dioxide, the silicon nitride, the fluororesin, the polyphenylene sulfide resin, There is provided a method characterized in that solder is attached to the joint portion by containing air in the polyamide, floating on the liquid surface, and rupturing.

According to invention of Claim 4 of this invention, it is the solder cream used in order to solder each unit on a board | substrate,
Including a plurality of particles made of magnesium, aluminum, titanium or alloys thereof, silicon, silicon dioxide, silicon nitride, fluorine resin, polyphenylene sulfide resin, polyamide,
By melting the solder cream, the plurality of particles float on the solder liquid surface.

  According to a fifth aspect of the present invention, the particles include the magnesium, the aluminum, the titanium, or an alloy thereof, the silicon, the silicon dioxide, the silicon nitride, the fluororesin, the polyphenylene sulfide resin, There is provided a solder cream characterized in that air is contained in polyamide, and the plurality of particles float and rupture on the solder liquid surface.

  By providing the method and solder cream of the present invention, soldering can be easily performed and defective products can be reduced. By reducing the number of defective products, the yield can be improved and the product can be provided at a low cost.

  Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments. A method of applying solder cream to a substrate and soldering each unit such as a terminal and a semiconductor device such as a large scale integrated circuit (LSI) or a semiconductor integrated circuit (IC) will be described. FIG. 1 is a diagram illustrating a substrate. As the substrate 1, for example, a printed circuit board made of a synthetic resin plate that is wired with a copper foil or the like on the surface and used by attaching an electrical component such as an integrated circuit or a resistor can be used. In FIG. 1, an electrode 2 for electrical connection with each unit is shown enlarged. For example, the electrode 2 is electrically connected to another electrode by wiring provided inside the substrate 1.

  FIG. 2 is a diagram showing a solder cream applied on the electrode. The solder cream 3 is applied on the electrode 2 in order to solder, for example, terminals and wiring portions of the semiconductor device and the electrode 2 exposed on the surface of the substrate 1. The application of the solder cream 3 is performed by, for example, using a mask having a window that matches the size and shape of the terminal, and printing the solder cream 3 on the surface of the terminal using a urethane resin or aluminum squeegee. It can be applied to the desired part.

  In the present invention, the solder cream 3 is not only tin-lead solder but also tin-silver-copper solder, tin-nickel-copper solder, tin-silver-bismuth-copper solder, tin-silver as lead-free solder. A powder of indium-bismuth solder, tin-silver solder, tin-antimony solder is used, flux is added to the powder, and the powder is made into a paste containing particles having a specific gravity smaller than that of the solder. The said solder can use the metal composition conventionally known. In the present invention, a particle having a small specific gravity means that the particle has a small specific gravity of about 7 to 9 of the solder. Therefore, if the solder has a specific gravity of 9, it may have any value as long as the specific gravity is less than 9. In the present invention, when the solder is melted, it is preferable that it floats rapidly on the solder liquid surface, that is, the specific gravity is small. This is because the particles can be protruded from the liquid surface by the driving force as the particles rapidly float, and the solder can be attached to the joint portion of the unit that is further away. Moreover, not only the particles but also the liquid level can be raised by the propulsive force, and the solder can be adhered widely to the separated joint portions. Further, the joint portion separated from the liquid surface is adjacent, for example, 0.05 mm, and solder is attached to the joint portion separated from the liquid surface by soldering. It can also be satisfied. In the present invention, magnesium or aluminum, which is a metal having a specific gravity smaller than that of solder, or an alloy thereof is preferable. Magnesium has a specific gravity of 1.74, and aluminum has a specific gravity of 2.70.

  Moreover, the particle | grain can use a thing of a suitable magnitude | size from the space | interval between the junction part of each unit and the solder liquid surface which deform | transformed by heating, and the application | coating thickness of a solder cream. In the present invention, in order to adhere solder, magnesium, aluminum, or an alloy thereof containing air can also be used. This is because the solder floats on the solder liquid surface due to melting of the solder and ruptures due to the expansion of air, so that the solder can be scattered and adhered to the separated joint portions of each unit. In this case, it is preferable to float on the liquid surface and rupture at a position near the liquid surface, but may rupture in the solder liquid. When ruptured in the solder liquid, the liquid level rises at the ruptured position, and by the liquid level rise, the solder can be attached to the separated joint portions of each unit.

  In the present invention, any material may be used as long as the specific gravity is smaller than that of the solder component, not limited to the above-described magnesium, aluminum, and alloys thereof. As other materials, plastic, silicon, silicon dioxide, silicon nitride, titanium, titanium alloy, and the like can be used. As the plastic, since the melting point of the solder is about 200 ° C., a plastic having a melting point of 200 ° C. or more is preferable. For example, tetrafluoroethylene resin (PTFE), polytetrafluoroethylene-ethylene copolymer ( ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), a fluororesin, polyphenylene sulfide resin, polyamide, or the like can be used. As the flux, for example, pinewood (rosin) can be used.

  In the present invention, it is possible to mix particles of an appropriate number, amount and size according to the number of units that are deformed by heating. Furthermore, in this invention, you may contain nitrogen, a carbon dioxide gas, etc. other than air inside. The shape of the particles may be any shape, but when it bursts, a spherical shape that scatters evenly is preferable.

  FIG. 3 is a diagram showing a place where each unit is arranged on a solder cream applied to a predetermined position of the substrate. In FIG. 3, each unit 4 is arrange | positioned so that the applied solder cream may be covered. After each unit 4 is arranged as shown in FIG. 3, it is placed in a reflow soldering apparatus, heated to about 200 ° C. to about 300 ° C. to melt the solder cream, and then soldered by cooling. I do. Note that the reflow soldering apparatus includes, for example, an air reflow apparatus that forcibly circulates air and a nitrogen reflow apparatus that performs in a nitrogen atmosphere, a container, a fan that forcibly circulates air and nitrogen, and a heater that heats the air to a predetermined temperature. It is comprised including.

  FIG. 4 is a diagram showing a substrate on which each unit is arranged and heated in a reflow soldering apparatus. FIG. 4A is a cross-sectional view showing a place where a substrate on which each unit is arranged is arranged in a reflow soldering apparatus. A solder cream 3 is applied on the surface of the substrate 1, and a unit 4 is disposed on the solder cream 3. As shown in FIG. 4 (a), the solder cream 3 is applied so that the surface is substantially flat and parallel to the surface of the substrate 1, and the unit 4 has a bottom portion that serves as a joining portion on the solder cream 3. It is arranged to be embedded. Thereby, the bottom part used as the junction part of the unit 4 is soldered by melt | dissolving the solder cream 3 and cooling after that.

  FIG. 4B is a cross-sectional view showing a place where the unit 4 is warped by heating. In order to melt the solder cream 3, it is heated to about 200 ° C. to about 300 ° C. as described above. This heating causes a difference in thermal expansion between the substrate 1 and the unit 4 made of different materials, and causes warping. FIG. 4B shows that the end of the unit 4 is warped and the tip is separated from the melted solder cream 3. Note that this warp causes a height difference in the unit 4 and causes defective products. Further, this warpage occurs before the solder melts, and the solder is not attached to the separated portions.

  FIG. 5 is a diagram illustrating the movement of particles contained in the solder cream. FIG. 5A is a cross-sectional view showing a place where the unit 4 such as a terminal or a semiconductor device is placed on the solder cream 3 applied to the substrate 1 and heated as shown in FIG. 4B. In FIG. 5 (a), the substrate 1 with the unit 4 placed in a predetermined position is placed in the above-described reflow soldering apparatus, heated to about 200 ° C. to about 300 ° C., and the solder cream 3 is melted. Where it is. Further, the unit 4 is warped due to the heating, and the joining portion which is the bottom of the unit 4 and the surface of the solder cream 3 are separated from each other. In the embodiment shown in FIG. 5A, since the solder cream 3 has started to melt, a plurality of particles 5 are still uniformly dispersed.

  FIG. 5B is a diagram showing the solder cream melting and the particles floating. In the embodiment shown in FIG. 5 (b), the solder cream 3 is melted to become a solder solution, and the particles 5 contained in the solder solution are floating because of a small specific gravity. Part of the particles 5 floating on the solder liquid surface are exposed from the solder liquid surface and come into contact with the separated joint portions, thereby attaching the solder covering the surface of the particles 5 to the separated joint portions. Further, as the particles 5 float, the liquid level also rises, and by this liquid level rise, solder can be attached to the separated joint portions.

  In the method of the present invention, the substrate 1 is then cooled to room temperature and the solder is solidified. Cooling can be performed by stopping the heater. Alternatively, the heater can be quickly cooled by stopping the heater and rotating the fan. As shown in FIG.5 (b), when the particle | grains 5 exposed from the liquid level are adjacent to the spaced-apart joining part, when the solder is solidified and contracted, the separated joined part is drawn toward the substrate 1, Deformations such as warping are corrected. As described above, by using the method of the present invention, the unit 4 that has warped in the direction opposite to the substrate 1 side by heating is pulled toward the substrate 1 side as the solder is solidified, and the unit 4 before deformation is drawn. It can be corrected to the state. Actually, with cooling, the difference in thermal expansion becomes smaller, and deformations such as warping are slightly corrected. As shown in FIG. 5, even if the particles 5 are not adjacent to the separated joint portions, they are in an adjacent state by this correction, and deformation such as warping can be corrected by coagulating and shrinking the particles.

  In the present invention, for example, the specific gravity of the particles 5 is 2 as compared with the specific gravity 9 of the solder, so that the specific gravity is extremely small, so that the particles 5 are rapidly levitated due to melting of the solder, and the propelling force causes the liquid 5 to rise. The surface can be raised to deposit solder over a wider area of the spaced joints. Moreover, in the case of a thing with very small specific gravity, since it can stick to the part which protrudes from the liquid level and is distant, a particle diameter can be made small.

  FIG. 6 is a diagram illustrating the movement of particles when particles containing air are used. FIG. 6A is a cross-sectional view showing a place where a unit 4 such as a terminal or a semiconductor device is placed on the solder cream 3 applied to the substrate 1 and heated, as in FIG. In FIG. 6 (a), the substrate 1 with the unit 4 placed in a predetermined position is placed in the reflow soldering apparatus described above, heated to about 200 ° C. to about 300 ° C., and the solder cream 3 is melted. Where it is. Further, the unit 4 is warped due to the heating, and the joining portion which is the bottom of the unit 4 and the surface of the solder cream 3 are separated from each other. In the embodiment shown in FIG. 6A, since the solder cream 3 has started to melt, the plurality of particles 5 are still uniformly dispersed.

  FIG. 6B is a view showing a state where the solder adheres to the separated joint portions as the particles 5 float up in the solder liquid, and the air inside expands and bursts. For example, as described above, the specific gravity of the particles 5 is extremely small, and when ruptured after rapidly floating, the rupture occurs in the vicinity of the solder liquid surface, and the rupture causes a solder liquid as shown in FIG. Waves 6 can be generated on the surface, and solder can be scattered. Due to the generation and scattering of the waves, the solder can be attached to the joint portion separated from the liquid surface. FIG. 6B also shows a case where the solder liquid ruptures. Bubbles 7 are generated by the rupture, and waves 6 are generated by the bubbles 7, and solder is applied to the separated joints. It can also be attached. In addition, since the space | interval of a solder liquid surface and a junction part is a micro space | interval of several dozen micrometers, this micro space | interval can be satisfy | filled with a solder by adhesion to the junction part.

  The unit 4 and the substrate 1 can be soldered by cooling the solid space filled with the solder and solidifying the solder. When the solder solidifies, the solder contracts, whereby the joining portion is pulled toward the substrate 1 side, and deformation such as warpage is corrected.

  By using the method of the present invention described above, the difference in height of each unit to be soldered to the board is about 0.15 mm at the stage after heating, so that it falls within the standard 0.1 mm. I was able to. Many of the defective products so far have had a difference in height of each unit of electronic components of about 0.15 mm due to deformation. Therefore, by providing the method of the present invention and the solder cream for realizing the method, it is possible to remarkably reduce defective products and improve the yield, thereby providing electronic components at low cost. .

The figure which illustrated the board | substrate with which the electrode was formed in the predetermined position. The figure which showed the place which applied the solder cream on the electrode. The figure which showed the place which has arrange | positioned each unit on a solder cream. The figure which showed the place which has produced the curvature in the unit by heating. The figure which showed the place where the solder cream melt | dissolved and the particle | grains have floated on the solder liquid surface. The figure which showed the place which the wave produced in the liquid surface and the bubble was generated in the liquid by the burst of the particle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Electrode 3 ... Solder cream 4 ... Unit 5 ... Particle 6 ... Wave 7 ... Bubble

Claims (5)

A method of soldering each unit on a board,
Applying a solder cream comprising a plurality of particles having a specific gravity smaller than that of solder on the substrate;
Arranging each unit at a predetermined position on the substrate to which the solder cream is applied;
Heating the substrate on which the units are arranged to melt the solder cream;
Cooling the substrate on which the units are arranged,
In the melting step, the plurality of particles float on the solder liquid surface, and thereby solder is attached to the joint portion of the unit separated from the liquid surface by the heating.   The method of claim 1, wherein the particles are made from magnesium, aluminum, titanium or alloys thereof, silicon, silicon dioxide, silicon nitride, fluororesin, polyphenylene sulfide resin, polyamide.   The particles include air in the magnesium, the aluminum, the titanium, or an alloy thereof, the silicon, the silicon dioxide, the silicon nitride, the fluororesin, the polyphenylene sulfide resin, and the polyamide, and float on the liquid surface. The method according to claim 2, wherein solder is attached to the joint portion by bursting. A solder cream used to solder each unit onto a substrate,
Including a plurality of particles made of magnesium, aluminum, titanium or alloys thereof, silicon, silicon dioxide, silicon nitride, fluorine resin, polyphenylene sulfide resin, polyamide,
The solder cream according to claim 1, wherein the plurality of particles float on the surface of the solder liquid by melting the solder cream.   The particles include air in the magnesium, the aluminum, the titanium, or an alloy thereof, the silicon, the silicon dioxide, the silicon nitride, the fluororesin, the polyphenylene sulfide resin, and the polyamide, on the solder liquid surface. The solder cream according to claim 4, wherein the plurality of particles float and rupture.

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