JP2001308127A - Solder bump printing method and electronic component mounting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder bump printing method which can reduce the print quantity shortage of solder bumps. SOLUTION: Solder paste in holes 10a of a screen mask 10 is heated at a lower temperature than the melting point of its solder particles by hot air flow 8 and then the screen mask 10 is peeled off from a CSP 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solder projection printing method for printing a plurality of solder projections on a substrate or an electronic component by a solder paste printing method, and an electronic component mounting method using the same.

[0002]

2. Description of the Related Art Conventionally, semiconductor devices that are electronic components include:
For example, there is known a device such as a QFP (Quad Flat Pack) which has lead terminals extending in a gull wing shape around a package as bonding electrodes.

However, in this type of semiconductor device,
In order to increase the number of lead terminals (the number of I / Os) while maintaining the strength of the lead terminals extending around the package to some extent, the size of the package must be increased.

For this reason, in recent years, for example, LGA (La
nd Grid Array), BGA (Ball G
ride Array), CSP (Chip Size)
Semiconductor devices that include a plurality of microelectrodes provided in an array on the lower surface of a package as bonding electrodes, such as a package, are becoming mainstream. In these semiconductor devices, by providing the bonding electrode on the lower surface of the package, it is not necessary to employ a complicated three-dimensional structure such as a gull wing structure, so that the bonding electrode can be a minute electrode. As a result, the number of I / Os can be increased without increasing the size of the package.

[0005] In a process of mounting a semiconductor device having such minute electrodes on a mother board, a solder paste printing method may be used. For example, in an LGA having flat electrodes as microelectrodes, solder projections are printed on each of the microelectrodes by a solder paste printing method, or a plurality of solder projections are printed on a pad which is an electrode pattern of a mother board. Then, after mounting the LGA on the motherboard so that the solder projections and the pads are overlapped, the solder particles in the solder projections are melted by a reflow furnace method, hot air irradiation, laser irradiation, or the like. Further, the flattened electrode and the pad of the motherboard are connected by soldering by curing the melted solder. Further, for example, each bonding electrode is a protruding electrode (bump electrode) protruding from the lower surface of the package, and the protruding electrode is formed of a solder ball.
For GA and CSP, solder projections corresponding to each protruding electrode are placed on the mother board pads to reduce the positional deviation on the mother board after mounting and to make more reliable solder connection. Sometimes printed.

[0006]

However, in the conventional solder paste printing method, for example, after filling each hole of a stencil mask closely adhered to a mother substrate with a solder paste, the stencil mask is peeled off from the mother substrate. Since a part of the solder paste in the hole is dragged by the inner wall of the hole, untransferred solder paste is left in each hole. As a result, the printed amount of the solder protrusion may be insufficient. Further, as a result of such a shortage of the printing amount, the soldering between the pad of the mother board and the bonding electrode of the semiconductor device may be insufficient, causing a conduction failure.

[0007] These are problems when a stencil mask is used in the solder paste printing method, but the same problem may occur even when an intaglio mask is used. A similar problem may occur not only when the semiconductor device is mounted on the motherboard but also when other electronic components having a bonding electrode on the lower surface of the main body are mounted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a first object of the present invention is to provide a solder projection printing method capable of reducing the shortage of the solder projection printing amount.

A second object of the present invention is to provide an electronic component mounting method capable of reducing a conduction failure between a substrate and an electronic component caused by a shortage of a printed amount of a solder projection. .

[0010]

In order to achieve the first object, a first aspect of the present invention is a solder for printing a plurality of solder projections on a substrate or an electronic component by a solder paste printing method using a stencil. In the projection printing method, a contacting step of bringing the stencil into close contact with the substrate or the electronic component, a filling step of filling each of the holes of the stencil with the solder paste, and filling the filled solder paste with a melting point of the solder particles. A heating step of heating at a low temperature to volatilize a solvent in the solder paste and a peeling step of peeling the stencil from the substrate or the electronic component are performed.

In this solder projection printing method, unlike the conventional solder paste printing method in which the peeling step is performed immediately after the filling step, prior to performing the peeling step,
The solder paste filled in each hole of the stencil is heated at a temperature lower than the melting point of the solder particles inside the stencil to volatilize the solvent in the solder paste. Then, by this volatilization, at least the outer portion of the solder paste is solidified. The present inventors have intensively studied and, by solidifying the solder paste in this way, improve the removability of the solder paste from inside the hole,
It has been found that the shortage of the printed amount of the solder protrusion on the substrate or the electronic component can be reduced. In addition, a cause that can improve the removability of the solder paste in the present solder projection printing method involves lowering the adhesiveness between the outer portion and the inner wall of the hole by solidifying at least the outer portion of the solder paste. It is thought that it is. According to the inventor's intensive research, the solder paste thus solidified is heated at a temperature exceeding the melting point in the heating step, and is changed from a solder paste to a solder solid. Also,
It has been found that poor conduction between the electronic component and the substrate is unlikely to occur. The cause is considered as follows. That is,
The solder paste solidified in the heating step of the present solder projection printing method does not fuse individual solder particles, unlike the solder paste that is melted to become a solder solid. On the other hand, the solid solder has a more rounded shape than in the solder paste state due to surface tension or the like generated when the solder particles are fused. Therefore, the solidified solder paste and the solder solid material obtained by fusing the solder particles are more rounded, and the contact area between the printed solder projection and the substrate or electronic component is reduced. In other words, the solder protrusions derived from the former have a larger contact area with the substrate or the electronic component. In the mounting step, the solder particles are melted and hardened while being brought into contact with the substrate or the electronic component more reliably than the solder projection derived from the latter in the mounting process, so that the substrate and the electronic component are more securely soldered. It is thought to connect.

According to a second aspect of the present invention, there is provided a solder projection printing method for printing a plurality of solder projections on a substrate or an electronic component by a solder paste printing method using an intaglio, wherein each recess of the intaglio is filled with a solder paste. A step of bringing the intaglio plate into close contact with the substrate or the electronic component so that the opening of each concave portion and the substrate or the electronic component are aligned with each other, and applying a solder paste in each concave portion at a temperature lower than the melting point of the solder particles. A heating step of heating to evaporate the solvent in the solder paste and a peeling step of peeling the intaglio from the substrate or the electronic component are performed.

[0013] In this solder projection printing method, the same effect as the solder projection printing method of the first aspect is used to improve the releasability of the solder paste from inside the concave portion of the intaglio plate, and to print the solder projection on the substrate or electronic component. Reduce shortages.

According to a third aspect of the present invention, in the solder projection printing method of the first or second aspect, the stencil plate or the intaglio plate is made of a resin obtained by ablating a hole or a recess in a resin material. Things.

In this solder projection printing method, a resin stencil or intaglio having holes and recesses formed by ablation processing, such as a so-called plastic mask, is used. In such a stencil or intaglio, for example, a metal mask
The inner wall of the hole and the inner wall of the recess are much more excellent in smoothness than those having the hole and the recess processed by the photolithography method or the etching method. Therefore, the frictional force between the solder paste solidified in the hole or the recess and the inner wall of the hole or the recess becomes smaller than that of a metal mask or the like. As a result, the removability of the solder paste from the inside of the hole or the concave portion is further improved, and the shortage of the printed amount of the solder protrusion is further reduced. However, resin stencils and intaglios are more liable to be deformed by heating than metal stencils, and this deformation may cause a new problem of causing defective printing positions of solder projections.

Therefore, a fourth aspect of the present invention is the solder projection printing method according to the third aspect, wherein a polyimide resin is used as the resin material.

In this solder projection printing method, a stencil or intaglio made of polyimide resin having heat resistance is used. The stencils and intaglios having such a configuration have less deformation due to heating than those made of other resins. In particular, the melting point of solder particles, 200
It is hardly deformed by heating at about [° C]. For this reason, it is possible to reduce the defective printing position of the solder projection due to the deformation of the stencil or the intaglio caused by the heating.

According to a fifth aspect of the present invention, there is provided a printing step of printing a plurality of solder projections on a substrate or an electronic component by a solder projection printing method, a mounting step of mounting the electronic component on the substrate, A melting step of melting the projections by heating,
An electronic component mounting method for mounting the electronic component on the substrate by performing a hardening step of hardening the melted solder protrusion by cooling and solder-connecting the electrode pattern of the substrate and the joining electrode of the electronic component by soldering; Wherein the method of claim 1, 2, 3 or 4 is used as the solder projection printing method.

In this electronic component mounting method, by using the solder projection printing method of the first, second, third, or fourth aspect in the printing process, the shortage of the printed amount of the solder projection on the substrate or the electronic component is reduced. Therefore, it is possible to reduce the conduction failure between the substrate and the electronic component caused by the insufficient printing amount in the curing step.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment to which the present invention is applied, an electronic circuit mounting method for mounting a CSP on a motherboard (hereinafter referred to as a mounting method) will be described.

In this mounting method, first, a contact step of bringing a screen mask as a stencil into close contact with the CSP, a filling step of filling each hole of the contacted screen mask with a solder paste, and a heating step of heating the filled solder paste. A solder paste printing step of performing a step and a peeling step of peeling the screen mask from the CSP is performed. Next, a mounting step of placing the CSP that has passed through the solder paste printing step on the motherboard, and a reflow step of melting the solder protrusions obtained by the solder paste printing step by heating. And a hardening step of hardening the melted solder protrusion by cooling.

FIGS. 1A to 1C and FIG. 2A
(C) is an explanatory diagram showing a work flow of the solder paste printing step. In FIG. 1A, reference numeral 4 denotes a CSP 4. On the lower surface of the CSP, projecting electrodes (bump electrodes) as bonding electrodes composed of a pad 4a and a solder ball 4c welded thereto are arranged in an array. It is arranged. In the solder paste printing step,
First, such a CSP 4 is set on the positioning jig 9 such that its lower surface faces upward. And FIG.
As shown in (b), the screen mask 10 is
After that, the squeegee 11 as shown in FIG.
Is filled with the solder paste 12 in each hole 10a of the screen mask 10 (filling step). This solder paste 1
2 contains a myriad of solder particles and a flux that removes an oxide film of the solder particles when the solder is melted, and further contains a resin component and a solvent in the flux.

According to the experiments of the present inventors, prior to bringing the screen mask 10 into close contact with the CSP 4 in the above-mentioned contact step, a flux is applied to the solder balls 4c of the CSP 4 in advance, so that the solder is applied. The short circuit between the electrodes caused by the oozing of the paste 12 was significantly reduced. Therefore, solder bar 4 of CSP4
It is desirable that the screen mask 10 be brought into close contact with the CSP 4 after applying a flux on the upper surface in advance.

After completing the operation shown in FIG. 1C, next, FIG.
As shown in (a), a hot air nozzle 7 is provided on the upper side of the screen mask 10, and hot air 8 is blown toward the screen mask 10 to heat the solder paste 12.
The solvent in the solder paste 12 is volatilized (heating step).
At this time, care should be taken not to heat the solder paste 12 higher than the melting point of the solder fine particles therein. Then, at least the outer portion (the portion exposed from the opening of the hole 10a and the contact portion with the inner wall of the hole) of the solder paste 12 is solidified by volatilization of the solvent. Further, as shown in FIG. 2B, after removing the hot air nozzle 7, air is blown toward the screen mask 10 by a blowing means (not shown) to cool the solder paste 12. Then, as shown in FIG. 2C, the screen mask 10 is removed from the CSP 4
The solder projections made of the solder paste 12 whose outer portion is solidified are transferred and printed on the solder balls 4c of the SP4.

As a method of heating the solder paste 12, a method of placing the CSP 4 in a furnace, a method of irradiating a laser, or the like may be used. As for the cooling of the solder paste 12, natural cooling may be performed without using the above-mentioned blowing means or the like, or may be omitted.

When the solvent in the solder paste 12 is volatilized in the heating step, the solder paste 12 slightly shrinks as shown in FIG. When the screen mask 10 is peeled from the CSP 4 in such a contracted state, FIG.
As shown in (b), the solder paste 12 can be smoothly separated from the holes 10a and transferred and printed on the solder balls 4c. Therefore, in the solder paste printing step of this mounting method, unlike the conventional solder paste printing method in which the solder paste 12 in the hole 10a is transferred and printed as it is, the removability of the solder paste 12 from the hole 10a is improved. At the very least, it is possible to reduce the shortage of the printed amount of the solder protrusion on the solder ball 4c. The cause that can improve the removability of the solder paste 12 as described above is considered as follows.
That is, it is considered that the solidification of at least the outer portion of the solder paste 12 reduces the adhesiveness between the outer portion and the inner wall of the hole.

For reference, the behavior of the solder paste 12 in the conventional solder paste printing method is shown in FIG. As shown in FIG. 4, in the conventional solder paste printing method, the screen mask in which the hole 10a is filled with the highly viscous solder paste 12 is peeled off from the CSP 4 as it is, so that the solder paste 12 is dragged on the inner wall of the hole. A large amount of the solder paste 12 remains in the hole 10a.

When solder projections are printed on the solder balls 4c as shown in FIG. 3 in the present mounting method, a solder paste 12 containing solder fine particles having a lower melting point than the solder balls 4c must be used. Is desirable. By using such a solder paste 12, it is possible to prevent the solder balls from being erroneously melted in the heating step.

FIG. 5 is a sectional view showing a state in which the solder fine particles of the solder paste 12 are erroneously melted due to excessive heating in the heating step. As shown,
Excessive heating that melts the solder particles causes the solder paste 12 to be transformed into the solder 5. The solder 5 volatilizes almost all the solvent and shrinks greatly compared to the state of the solder paste 12, and the tip portion is rounded due to the surface tension generated when the individual solder fine particles are fused. The solder protrusion made of the solder 5 having a round shape as described above comes into point contact with the substrate electrode 1a of the mother substrate 1 in a mounting step described later, as shown in FIG. On the other hand, as shown in FIG. 6B, the solder projection made of the solidified solder paste 12a which does not melt the solder fine particles and can exhibit good elasticity is brought into surface contact with the substrate electrode 1a. Become. For this reason, in a reflow process and a curing process described later, the substrate electrode 1a is more reliably melted and cured while being in contact with the substrate electrode 1a, so that poor solder connection (defective conduction) between the substrate electrode 1a and the pad 4b can be favorably suppressed. .

FIGS. 7A to 7C and FIG. 8 are explanatory diagrams showing the work flow of the mounting step. In this mounting step, first, as shown in FIG. 7A, another positioning jig 16 is placed on the positioning jig 9.
Then, the jigs are turned upside down, with the openings facing downward. Then, as shown in FIG. 7B, the CSP 4 is set on this other positioning jig 16 with the lower surface (solder ball surface) facing downward. After the CSP 4 is set on another positioning jig 16 in this way, as shown in FIG.
7 is brought up against the upper surface of the CSP 4. And
Thus, the CSP is set on the suction nozzle 17. Next, as shown in FIG. 8, on the X table 20 which slides in the left and right direction in the figure, and on the Y table 21 which slides in the depth direction in the figure, the mother substrate 1 which has been subjected to the above-mentioned removal step is completed. Is fixed. Then, an optical monitoring device 18 is interposed between the CSP 4 set on the component suction nozzle 17 and the mother board 1, and the optical monitoring device 1
8 while watching the image projected on the monitor 19 of the X.
By sliding the table 20 and the Y table 21,
Each board electrode 1a of the mother board 1 is positioned just below each solder ball 4c of the CSP 4 so as to be positioned. The optical monitoring device 18 combines the two-dimensional image of the CSP 4 on the upper side and the two-dimensional image of the mother board 1 directly below the CSP 4 so that their planar relative positions are the same as the real ones. The image is displayed on the monitor 19. After the positioning is performed while viewing the image projected in this manner, the optical monitoring device 18 is removed, the component suction nozzle 17 is slowly lowered vertically, and the CSP 4 is soft-touched to the mother substrate 1. When the vacuum function is stopped, the component suction nozzle 1 is stopped.
The CSP 4 is separated from 7 and mounted on the motherboard 1.

In this mounting step, it is desirable to apply a flux to at least one of the solder protrusions and the substrate electrode 1a by a brush, a nozzle, or the like before mounting (the same applies to a modified example described later). By applying the flux in this manner, the solder protrusions and the substrate electrodes 1 are formed.
This is because it is possible to increase the frictional force with respect to “a” and reduce the positional deviation between the two after mounting. In addition, it is better to avoid applying the solder paste 12 instead of the flux because an undesired short circuit may occur.

After the CSP 4 is mounted on the motherboard 1 in this manner, the above-described reflow step is performed.
Solder ball 4c and solder paste 12a interposed between board electrode 1a of mother board 1 and pad 4b of CSP 4
Is melted and fused. Next, the molten solder is cured by performing a curing step, and the board electrode 1a of the mother board 1 and the pad 4b of the CSP 4 are connected by soldering. By this solder connection, the CSP 4 is electrically and mechanically connected to the mother board 1 and mounted. The operation in the reflow step is the same as the operation shown in FIG. 2A, and the operation in the curing step is the same as the operation shown in FIG.

In the solder paste printing step of this mounting method, it is desirable to use a so-called plastic mask having holes 10a formed by ablation using an excimer laser or the like. In such a plastic mask, the smoothness of the inner wall of the hole is far superior to that of a metal mask having the hole 10a processed by the photolithography method or the etching method, and the removability of the solder 5 from the inside of the hole 10a is further improved. This is because it can be done.

As the resin material used for the plastic mask, it is desirable to use a polyimide resin. This is because a plastic mask made of a heat-resistant polyimide resin has less deformation due to heating than a resin mask made of another resin, and can reduce defective printing positions of solder protrusions due to deformation due to heating.

Next, a modification of the mounting method of the first embodiment will be described. FIGS. 9A to 9C are cross-sectional views each showing a part of a work flow in the mounting method of this modified example. In this mounting method, the solder protrusion is printed not on the solder ball 4c of the CSP 4 but on the electrode pattern (board electrode 1a) of the mother board 1. Specifically, FIG.
As shown in (a), after the screen mask 10 is brought into close contact with the mother substrate 1 (adhesion step), a solder paste 12 is filled into each hole 10a of the screen mask 10 with a squeegee 11 (filling step). Then, each hole 10a is formed by the same operation as that shown in FIGS. 2 (a) and 2 (b).
After subjecting the solder paste 12 inside to heat treatment and cooling treatment, the screen mask 10 is peeled off from the mother substrate 1 and a solidified solder paste 12a as shown in FIG.
Are printed with solder protrusions made of In such printing as well, the substrate electrode 1 is formed by transferring and printing the solidified and modified solder paste 12a instead of the uncured solder paste 12.
It is possible to reduce the shortage of the print amount of the solder protrusion on the “a”.

According to the experiments performed by the present inventors, even in the mounting method of the present modification, the substrate electrode 1a of the mother substrate 1 is preceded by bringing the screen mask 10 into close contact with the mother substrate 1 in the above-mentioned contact step. By applying the flux on the upper surface in advance, a short circuit between the electrodes caused by seepage of the solder paste 12 could be significantly reduced. Therefore, it is desirable that the screen mask 10 be brought into close contact with the mother substrate 1 after applying a flux on the substrate electrode 1a of the mother substrate 1 in advance.

After printing the solder protrusions, as shown in FIG. 9C, after mounting the CSP 4 on the mother substrate 1, the reflow step and the curing step may be performed.

As described above, in the embodiment and the modification, the CS
Although the mounting method for mounting P4 on the motherboard 1 has been described, it is needless to say that the present invention can be applied to a mounting method for mounting other electronic components such as BGA, LGA, QFP, LSI, and bare chip.

Although the mounting method using a screen mask in the printing process has been described, the present invention is also applied to a mounting method in which a printing process is performed in which an intaglio in which each recess is filled with a solder paste is closely attached to a mother board or an electronic component. Is possible.

According to the first, second, third or fourth aspect of the present invention, there is an excellent effect that it is possible to reduce the shortage of the printed amount of the solder projection on the substrate or the electronic component.

In particular, according to the third aspect of the present invention, there is an excellent effect that the releasability of the solder paste from the inside of the hole or the concave portion can be further improved, and the shortage of the printed amount of the solder protrusion can be further reduced. .

In particular, according to the fourth aspect of the present invention, there is an excellent effect that it is possible to reduce a printing position defect of a solder projection due to deformation of a stencil or an intaglio caused by heating.

According to the fifth aspect of the present invention, there is provided an excellent effect that it is possible to reduce poor conduction between the substrate and the electronic component due to insufficient printing of the solder projection on the substrate or the electronic component. is there.

[Brief description of the drawings]

FIGS. 1A to 1C are explanatory diagrams each showing a work flow of a solder paste printing step of a mounting method according to an embodiment.

FIGS. 2A to 2C are explanatory diagrams each showing a continuation of the same work flow.

FIGS. 3A and 3B are cross-sectional views showing the behavior of a solder paste 12 in the solder paste printing step.

FIG. 4 is a cross-sectional view showing the behavior of a solder paste in a conventional solder paste printing method.

FIG. 5 shows a heating step in the solder paste printing step.
FIG. 6 is a cross-sectional view showing a state in which solder particles of the solder paste 12 are erroneously melted by excessive heating.

FIG. 6A is a cross-sectional view showing a contact state between a solder projection and a substrate electrode obtained after such melting. (B)
FIG. 4 is a cross-sectional view showing a contact state between a solder protrusion and a substrate electrode obtained without melting solder fine particles.

FIGS. 7A to 7C are explanatory diagrams each showing a work flow of a mounting step of the mounting method.

FIG. 8 is an explanatory diagram showing a continuation of the work flow.

FIGS. 9A to 9C are cross-sectional views each showing a part of a work flow in a mounting method according to a modified example of the embodiment.

[Explanation of symbols]

 Reference Signs List 1 mother board 1a substrate electrode 4 CSP 4a package 4b pad 4c solder ball 5 solder 6 stage 7 hot air nozzle 8 hot air 9 positioning jig 10 screen mask 11 squeegee 12 solder paste 12a solder paste (solidified) 16 positioning jig 17 component suction nozzle 18 Optical monitoring device 19 Monitor 20 X table 21 Y table

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H05K 3/34 505 H01L 21/92 604H

Claims (5)

[Claims] 1. A solder projection printing method for printing a plurality of solder projections on a substrate or an electronic component by a solder paste printing method using a stencil, comprising: a step of bringing the stencil into close contact with the substrate or the electronic component; A filling step of filling each hole of the stencil with a solder paste, a heating step of heating the filled solder paste at a temperature lower than the melting point of the solder particles to volatilize a solvent in the solder paste, And a peeling step of peeling off from the substrate or the electronic component. 2. A solder projection printing method for printing a plurality of solder projections on a substrate or an electronic component by a solder paste printing method using an intaglio, wherein a filling step of filling each recess of the intaglio with a solder paste; A step of bringing the intaglio plate into close contact with the substrate or the electronic component so that the opening of the substrate or the electronic component is brought into contact with the substrate, and heating the solder paste in each concave portion at a temperature lower than the melting point of the solder particles to form the solder. A solder projection printing method, comprising: a heating step of volatilizing a solvent in a paste; and a peeling step of peeling the intaglio from the substrate or the electronic component. 3. A solder projection printing method according to claim 1, wherein said stencil or intaglio is made of resin obtained by ablating said holes or recesses in a resin material. 4. The solder projection printing method according to claim 3, wherein a polyimide resin is used as the resin material. 5. A printing step of printing a plurality of solder projections on a substrate or an electronic component by a solder projection printing method, a mounting step of mounting the electronic component on the substrate, and melting the solder projections by heating. Mounting the electronic component on the substrate by performing a melting step of causing the electronic component to be solder-bonded to the electrode pattern of the substrate and a bonding electrode of the electronic component by hardening the molten solder protrusion by cooling. The electronic component mounting method according to claim 1, wherein the solder protrusion printing method is used.
An electronic component mounting method, characterized in that a method of mounting an electronic component is used.