JP2000176678A - Cream solder and packaging product using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cream solder and a rackaging product using it capable of restraining the remains of solder balls on a board when an electronic part is mounted on the board. SOLUTION: This cream is used when an electronic part 15 is mounted on a printed board 11. The cream solder is provided with eutectic solder 13b and metallic grain (Ag grain 13a) having a melting point higher than that of eutectic solder, and metallic grain is wholly diffused into eutectic solder when it is heated up to 220 deg.C. Thus, the remains of solder balls on the board are restrained when the electronic part is packaged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cream solder and a mounted product using the same. In particular, the present invention relates to a cream solder capable of suppressing a solder ball from remaining on a substrate when an electronic component is mounted on the substrate, and a mounted product using the same.

[0002]

2. Description of the Related Art FIGS. 3A to 3C are cross-sectional views showing a method for mounting an electronic component on a mounting board using a conventional cream solder. First, as shown in FIG. 3A, the printed circuit board 1 is printed by screen printing or a dispenser or the like.
A cream solder 113 is printed on 11. This cream solder 113 uses eutectic solder. Next, the electronic component 115 having the electrode 115a is mounted on the cream solder 113 so as to be pressed. At this time, the electronic component 15 is not pressed until it directly touches the printed board 111. Therefore, the electrode 115 of the electronic component 115
a between the solder paste 11 and the printed circuit board 111.
There are three. The temperature atmosphere in this state is room temperature.

After that, the printed circuit board 111 on which the electronic components 115 are mounted is inserted into a reflow furnace (not shown). In the reflow furnace, the printed circuit board 111 is first preheated. In this preheating, the viscosity of the flux contained in the cream solder 113 decreases and the cream solder 113 flows, but does not change much from the state at room temperature. Preheating temperature is 150 ℃
Before and after.

Next, in the reflow furnace, main heating of the printed circuit board 111 is performed. In this main heating, the printed circuit board 111 is heated to a temperature higher than the melting point of the solder (180 ° C. or higher for eutectic solder).

As shown in FIG. 3 (b), in the initial state of the main heating, the cream solder
13 begins to melt, and the cream solder 113 begins to wet the electrodes of the printed circuit board 111 and the electrodes 115 a of the electronic component 115. At the same time, the melted cream solder 1
Due to the surface tension of the solder 13, the solder 113 starts to gather on the electrodes of the printed circuit board 111 and the electrodes 115 a of the electronic component 115. Further simultaneously, cream solder 1
The electronic component 115 sinks into the solder 113 due to the wetting (affinity) of the substrate 13 and contacts the electrodes of the printed circuit board 111.

Thereafter, as shown in FIG. 3C, in the later stage of the main heating, the solder 113 is cooled after forming a fillet. As a result, the electronic component 115
The solder 113 is joined to the substrate electrode in a stable posture.

[0007]

As described above, eutectic solder is mainly used as a conventional solder bonding agent for high-density mounting. After the reflow, as shown in FIG. 3 (c), the surface tension of the molten solder does not concentrate on the pattern on the regular substrate, and the pattern and the periphery of the component are, for example, φ100 μm.
A small size solder ball 117 may remain.
This is not a problem in quality of the electronic component 115 having a relatively large pitch. That is, even if the remaining solder balls 117 are not removed by washing,
When the distance between the electrodes 115a is relatively large, the insulation between adjacent electrodes is not particularly deteriorated. Also, since the solder balls 117 are wrapped in flux,
Even after the product is completed, there is almost no accident that the solder balls 117 fall off the substrate 111 and short-circuit other parts.

[0008] However, portable electronic products have been actively sold to the market, and further reductions in the size and weight of mounting boards have been studied and introduced. For this reason, the interval between the component and the electrode is narrowed (narrow pitch). For example, even a solder ball of φ100 μm may be considered as a cause of deteriorating the insulating property between the electrodes, and is becoming a problem. In addition, surplus solder, which often becomes solder balls, causes bridges, and measures for these are important.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and has as its object to provide a cream solder capable of suppressing the occurrence of solder balls remaining on a substrate when an electronic component is mounted on the substrate, and a cream solder therefor. An object of the present invention is to provide a mounting product that uses the same.

[0010]

Means for Solving the Problems In order to solve the above problems, a cream solder according to the present invention is a cream solder used when electronic components are mounted on a substrate, and comprises a eutectic solder and a eutectic solder. Metal particles having a melting point higher than the melting point, wherein the metal particles are all diffused into the eutectic solder when heated to about 220 ° C.
Further, it is preferable that the metal particles are contained in an amount of 1 to 10%. Further, it is preferable that the metal particles are contained in an amount of 1 to 10%, and the metal particles are Ag, Cu, Sn, or an alloy thereof.

In the cream solder, eutectic solder and
Metal particles having a melting point higher than the melting point of the eutectic solder. Therefore, when the cream solder is melted in a reflow furnace to mount the electronic components on the board, the metal particles are slower to melt than the eutectic solder, so the electronic components mounted on the board are completely submerged. First, there is a period in which the substrate remains floating from the substrate. Thereby, the solder balls can be prevented from remaining on the board after mounting.

A mounting product according to the present invention includes a mounting substrate, an electronic component mounted on the mounting substrate, and a cream solder for joining the electronic component and the mounting substrate. Eutectic solder and metal particles having a melting point higher than the melting point of the eutectic solder, wherein the metal particles are all diffused into the eutectic solder when heated to about 220 ° C. And

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 (a) to 1 (c)
FIG. 4 is a cross-sectional view showing a method of mounting an electronic component on a mounting board using cream solder according to an embodiment of the present invention.

First, as shown in FIG. 1A, cream solder 13 having a thickness of, for example, about 150 μm is printed on a printed board 11 by screen printing or a dispenser. The cream solder 13 is obtained by mixing about 1 to 10 wt% of Ag particles 13a with a eutectic solder 13b. The mixing amount of the Ag particles is preferably an amount capable of reflowing in the same profile as the cream solder containing no Ag particles. The particle size of the Ag particles 13a is, for example, about 30 μm, and the particle size of the eutectic solder 13b is, for example, about 30 μm. The particle size of the Ag particles 13b is preferably equal to or larger than the particle size distribution of the cream solder 13, but is preferably up to a size that does not impair printability and dischargeability.

Next, the electronic component 15 having the electrode 15a is mounted on the cream solder 13 so as to be pressed. At this time, the electronic component 15 is not pressed until it directly touches the printed board 11. Therefore, the cream solder 13 exists between the electrode 15 a of the electronic component 15 and the printed board 11. The temperature atmosphere in this state is room temperature.

Thereafter, the printed circuit board 11 on which the electronic components 15 are mounted is inserted into a reflow furnace (not shown). In this reflow furnace, first, the pre-heating of the printed circuit board 11 is performed. In this preheating, the cream solder 13
, The viscosity of the flux contained in the solder decreases, and the cream solder 13 flows, but does not change much from the state at room temperature. The preheating temperature is around 150 ° C.

Next, main heating of the printed circuit board 11 is performed in a reflow furnace. In this main heating, the printed circuit board 11 is heated to a temperature equal to or higher than the melting point of the solder (180 ° C. or higher for eutectic solder).

As shown in FIG. 1B, in the initial state of the main heating, the cream solder
3 begins to melt, and the cream solder 13 starts to wet the electrodes of the printed circuit board 11 and the electrodes 15 a of the electronic component 15. At the same time, due to the surface tension of the melted cream solder 13, the solder 13 starts to collect on the electrodes of the printed circuit board 11 and the electrodes 15 a of the electronic component 15. Further simultaneously, the wetting (affinity) of the cream solder 13
As a result, the electronic component 15 sinks into the solder 13 and moves in a direction in contact with the printed circuit board 11.

At this stage, the Ag particles 13a have not yet been dissolved. Accordingly, the undissolved Ag particles support the electronic component 15 on the printed circuit board 11, and the component 15 does not sink completely, and the component 15 remains floating from the substrate 11. Thus, the electronic component 15
Is more solder 13 than the conventional product by the amount that
Is large, the concentration of the solder 13 on the substrate electrode and the electrode 15a of the electronic component 15 due to the surface tension of the solder 13 is likely to be increased. Thus, the amount of the solder 13 spread in the initial stage of the main heating and remaining as a solder ball in the latter stage of the main heating can be significantly reduced.

Thereafter, as shown in FIG. 1 (c), in the latter half of the main heating, 230% of the solder 13 is placed in the reflow furnace.
The solder 13 is heated up to a temperature of from about 240 ° C. to 240 ° C., and forms a fillet as in the related art, and then cooled. Due to the heat of the latter half of the main heating, the particle size of the Ag particles 13a gradually decreases, and diffuses into the melted solder 13, and finally, the Ag particles 13a become in the same state as the melted state. Then, the electrode 15 a of the electronic component 15 that has lost support comes into contact with the electrode of the printed circuit board 11. As a result, the electronic component 15
Is bonded to the substrate in a stable posture by the solder 13.

According to the above embodiment, since the solder particles 13 contain about 1 to 10 wt% of the Ag particles 13a, when the cream solder 13 is melted in a reflow furnace, the Ag particles 13a are removed from the eutectic solder 13b. Is slower to melt, so that the component 15 does not sink completely as described above, and the component 15 remains floating from the substrate 11. Thus, the amount of the solder 13 spread in the initial stage of the main heating and remaining as a solder ball in the latter stage of the main heating can be significantly reduced. Therefore, the rate of occurrence of solder balls can be significantly reduced, and the average particle size of the generated solder balls can be reduced.
Therefore, the quality of the mounting board having a narrow pitch can be improved.

In a mounting board having a relatively coarse pitch,
This eliminates the need for a visual inspection of the state of generation of solder balls for maintaining the quality of electronic components mounted on the board.
For this reason, productivity and quality can be improved.

In addition, by suppressing the generation of solder balls as described above, it is possible to suppress the deterioration of the insulation between the electrodes in a portable electronic product even if the distance between the components and the electrodes is reduced. Therefore, it is possible to increase the density from the viewpoint of quality without being particular about the reduction in size and size for portable use, which leads to the miniaturization of products. In addition, it leads to resource saving of electronic equipment products, which leads to preservation of the global environment.

In the above embodiment, the eutectic solder 13
Although cream solder 13 containing Ag as particles is used for b, cream solder containing other metals as particles for eutectic solder 13b can also be used. The other metal preferably diffuses into the eutectic solder melted at around 220 ° C. For example, it is also possible to use a cream solder in which an eutectic solder contains an Ag alloy or Cu as particles.

FIG. 2 is a diagram showing the number of solder balls generated in a conventional mounted product using cream solder and the generated number of solder balls in a mounted product using cream solder according to the above embodiment.

In FIG. 2, solder type A shows the case of a mounted product using eutectic solder, and solder types B and C use eutectic solder containing 1 to 10 wt% Ag particles. This shows the case of a mounted product. The amount of the Ag particles included in the type B is larger than the amount of the Ag particles included in the type C. The component size is 1005R, 1005C
Is 1.0 mm × 0.5 mm, and 1608R,
1608C is 1.6 mm × 0.8 mm.

The large ball size means a case where a relatively large solder ball remains, and the small ball size means a case where a relatively small solder ball remains. FIG. 2 shows the number of solder balls remaining when components are mounted on a board using the conventional cream solder A,
It is a result of examining the number of remaining solder balls when components are mounted on a board using cream solders B and C according to the present embodiment. From these results, it was confirmed that when the cream solder according to the present embodiment was used, the rate of occurrence of solder balls was lower than when the conventional cream solder was used. This is because there is a difference in the melting behavior of the cream solder as described above.

[0028]

As described above, according to the present invention, it is possible to provide a cream solder capable of suppressing a solder ball from remaining on a substrate when an electronic component is mounted on the substrate, and a mounted product using the same. Can be.

[Brief description of the drawings]

FIGS. 1A to 1C are cross-sectional views illustrating a method of mounting an electronic component on a mounting board using cream solder according to an embodiment of the present invention.

FIG. 2 is a diagram showing the number of solder balls generated in a conventional mounted product using cream solder and the generated number of solder balls in a mounted product using cream solder according to the embodiment.

FIGS. 3A to 3C are cross-sectional views showing a method for mounting an electronic component on a mounting board using a conventional cream solder.

[Explanation of symbols]

11: printed circuit board, 13: cream solder, 13a ...
Ag particles, 13b: eutectic solder, 15: electronic components, 15
a: electrodes, 111: printed circuit board, 113: cream solder, 115: electronic components, 115a: electrodes, 117: solder balls.

Claims (4)

[Claims] 1. A cream solder used for mounting an electronic component on a substrate, comprising: a eutectic solder; and metal particles having a melting point higher than the melting point of the eutectic solder, wherein the metal particles are approximately A cream solder characterized by being completely diffused into the eutectic solder when heated to 220 ° C. 2. The cream solder according to claim 1, wherein the metal particles are contained in an amount of 1 to 10%. 3. The cream solder according to claim 1, wherein the metal particles are contained in an amount of 1 to 10%, and the metal particles are Ag, Cu, Sn or an alloy thereof. 4. A mounting board, an electronic component mounted on the mounting board, and a cream solder for joining the electronic component and the mounting board, wherein the cream solder includes: a eutectic solder; A metal particle having a melting point higher than the melting point of the eutectic solder; wherein the metal particles are all diffused into the eutectic solder when heated to about 220 ° C.