JP2001170792A - Solder paste, and soldering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide solder paste to avoid generation of solder balls, and a soldering method using the solder paste. SOLUTION: The solder paste contains the solder powder, and the solder powder contains flat solder grains.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solder paste and a soldering method.

[0002]

2. Description of the Related Art Solder paste is disclosed in Japanese Patent Application Laid-Open No. 11-121.
No. 915, etc., solder powder,
The composition is a mixture of a flux, a solvent, and the like. As the solder powder, irregular or spherical solder particles are used.

Meanwhile, in order to cope with high-density mounting of various electronic devices, mounted components have been miniaturized, and the pitch between components has been narrowed. Under these conditions, when components are soldered to a mounting board using a conventional solder paste, various problems that have not conventionally been considered arise. One of them is the generation of solder balls and the resulting short circuit.

[0004] As described above, the conventional solder paste contains irregular or spherical solder particles as solder powder. When the component is soldered to the board by reflowing the solder paste, the solder particles that were independent in the solder paste before reflow agglomerate with each other in the reflow process, and a solder ball larger than the solder particles is generated. When the solder ball is generated, the solder ball short-circuits between terminal electrodes of adjacent components or lands on the mounting board at a narrow arrangement interval, thereby causing a failure due to a circuit short circuit.

[0005] Even if a short circuit has not yet occurred due to the solder ball at the time of reflow, the solder ball can be mounted on the mounting board by a slight impact during subsequent handling, transportation, or use by the user. Rolling on the top, resulting in a short circuit.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a solder paste and a soldering method capable of avoiding generation of solder balls.

[0007]

In order to solve the above-mentioned problems, a solder solder paste according to the present invention contains flat solder particles in a solder powder.

As described above, it has been found that the use of the solder powder containing the flat solder particles can avoid the generation of solder balls. The reason is presumed that the flat solder particles are unlikely to aggregate with each other when melted by heating such as reflow. In addition, in the case of application to a general solder paste, when flat solder particles coexist with irregular or spherical solder particles, the flat solder particles bridge between the irregular or spherical solder particles, This is presumed to be because aggregation of the irregular or spherical solder particles is prevented.

The content of the flat solder particles in the solder powder is 25% by weight based on the total weight of the solder powder.
wt% to 100 wt%. If it is less than 25 wt%,
Solder balls occurred. The content of the flat solder particles may be 100 wt%, and the entire solder powder may be occupied by the flat solder particles.

[0010] The solder powder may include spherical solder particles together with the flat solder particles. Also in this case, generation of solder balls can be avoided by satisfying the content of the flat solder particles described above.

In this case, in one embodiment, the flat solder particles can be made to have substantially the same weight as the spherical solder particles. Such conditions can be easily satisfied by flattening the spherical solder particles into flat solder particles. When the spherical solder particles are crushed flat, elliptical flat solder particles are obtained.

The flat solder particles have a maximum diameter Dm and a thickness t.
Is preferably selected such that the ratio (Dm / t) to the range of 2 <(Dm / t) ≦ 13. It has been found that with such an aspect ratio, generation of solder balls can be reliably avoided.

As a specific embodiment, the flat solder particles have a maximum diameter Dm of 30 μm or more and less than 45 μm and a thickness t in the range of 10 to 20 μm, and a maximum diameter Dm of 45 μm.
particles having a thickness t in the range of 7 to 14 μm in a range of m to less than 65 μm, and a maximum diameter Dm of 65 μm to 80 μm.
It can contain at least one kind of particles having a thickness t of 5 μm or less and a thickness of 5 μm to 10 μm.

According to the experimental data, the maximum diameter Dm is 65 μm.
It has been found that the inclusion of particles having a thickness t of at least m and a thickness in the range of 5 μm to 10 μm is extremely useful for avoiding generation of solder balls.

The solder paste according to the present invention contains a solder flux as its general composition. The content of the solder flux is preferably in the range of 5 wt% to 45 wt%. In particular, an excellent solder ball suppression effect can be obtained at 10 wt% to 35 wt%. If the solder flux content exceeds 45% by weight, the effect of suppressing solder balls is lost.

In the solder paste according to the present invention, various types of conventionally known fluxes can be used. In addition, adhesive resin,
A flux containing a curing agent (hereinafter referred to as an adhesive flux) can also be used. The present invention also discloses details of the above-mentioned adhesive flux and a soldering method using the above-mentioned solder paste.

[0017]

FIG. 1 is a view schematically showing flat solder particles contained in a solder paste according to the present invention. FIG. 1A is a plan view, and FIG. 1B is a front view.
The external shape of the flat solder particles may be arbitrary. In the drawing, flat solder particles having an elliptical outer shape are shown. Flat solder particles having such a shape are usually
The spherical solder particles supplied from the solder powder maker can be easily obtained by crushing them flat.
When the spherical solder particles are crushed flat, elliptical flat solder particles are obtained. The flat solder particles are
It has an elliptical shape with a maximum diameter of Dm and a thickness of t. The flat solder particles can be selected from Sn, Cu, Ag, Sb, Pb, In and Bi. To obtain a Pb-free solder paste, the solder powder is composed of a solder powder other than Pb. Other solder particles coexisting with the flat solder particles are selected from the same composition.

FIG. 2 is a diagram schematically showing the composition of a solder paste containing the flat solder particles shown in FIG. 1 and solder particles having other shapes. The illustrated solder paste includes flat solder particles 110 and spherical solder particles 12.
0 is included. These solder particles 110, 120
Is mixed with the flux 130.

Next, a description will be given, with reference to examples, of the state of occurrence of solder balls when components are soldered using the above-mentioned solder paste.

Example 1 Solder powder composed of flat solder particles having a maximum diameter Dm (see FIG. 1) of 30 to 80 μm was crushed by using a ball mill to crush solder powder composed of spherical solder particles having a particle diameter of 20 to 30 μm. I got However, the manufacturing method of the flat solder powder is not limited to the above-mentioned ball mill method.

Next, the obtained flat solder powder is classified using a mesh, and the maximum diameter Dm is 30 μm or more and 45 μm or more.
solder powder A1 composed of a group of solder particles less than m, solder powder B1 composed of a group of solder particles having a maximum diameter Dm of 45 μm or more and less than 65 μm, and a maximum diameter Dm of 65 μm
Solder powder C consisting of solder particles having a size of not less than 80 μm
1 was obtained.

In the above three types of solder powders A1 to C1, the degree of flattening of the solder particles is as follows. First, solder particles having a maximum diameter Dm of 30 μm or more and less than 45 μm have a thickness t in the range of 10 μm to 20 μm, and the ratio (Dm / t) between the maximum diameter Dm and the thickness t is 1.5 ≦ (Dm / t ) ≦ 4.5.

The solder particles having a maximum diameter Dm in a range of 45 μm or more and less than 65 μm have a thickness t in a range of 7-14 μm, and a ratio (Dm / t) of 3.2 ≦ (Dm / t) ≦ 9.2. Becomes

The solder particles having a maximum diameter Dm in the range of 65 μm to 80 μm have a thickness t in the range of 5 μm to 10 μm, and the ratio (Dm / t) is 6.5 ≦ (Dm / t) ≦ 16. .

In total, the degree of flattening of the solder powders A1 to C1 as a whole is in the range of 1.5 ≦ (Dm / t) ≦ 16.

Next, a solder paste prepared using the above-mentioned solder powder will be described with reference to examples.

<Embodiment 2> Maximum diameter Dm is 30 μm or more 4
Solder powder A1 consisting of a group of solder particles less than 5 μm
Solder powder composed of spherical solder particles having a particle size in the range of 20 to 30 μm was added and mixed to obtain a mixed solder powder A2.

The content of the flat solder particles with respect to the total weight of the solder powder was selected in four stages of 25 wt%, 50 wt%, 75 wt% and 100 wt%. The remainder is a solder powder containing spherical solder particles.

Next, a thermoplastic rosin flux was added to the mixed solder powder A2 to obtain a solder paste A3.

<Embodiment 3> The maximum diameter Dm is 45 μm or more and 6
Solder powder B consisting of solder particles in a range of less than 5 μm
1 and a solder powder composed of spherical solder particles having a particle size in the range of 20 to 30 μm was added and mixed to obtain a mixed solder powder B2.

The content of the flat solder particles with respect to the total weight of the solder powder was selected in four stages of 25 wt%, 50 wt%, 75 wt% and 100 wt%. The remainder is a solder powder containing spherical solder particles.

Next, a thermoplastic rosin flux was added to the mixed solder powder B2 to obtain a solder paste B3.

<Embodiment 4> The maximum diameter Dm is 65 μm or more and 8
Solder powder C1 consisting of solder particles of 0 μm or less,
Solder powder composed of spherical solder particles having a particle diameter in the range of 20 to 30 μm was added and mixed to obtain a mixed solder powder C2.

The content of the flat solder particles with respect to the total weight of the solder powder was selected in four stages of 25 wt%, 50 wt%, 75 wt% and 100 wt%. The remainder is a solder powder containing spherical solder particles.

Next, a thermoplastic rosin flux was added to the mixed solder powder C2 to obtain a solder paste C3.

<Comparative Example 1> For comparison, a particle size of 20 to 30 was used.
Solder powder consisting of only μm spherical solder particles was used, and a thermoplastic rosin flux was added to the solder powder to obtain a solder paste D3. The content of the flux was fixed at 10 wt% with respect to the weight of the solder powder.

The occurrence of solder balls was determined for Examples 2 to 4 and Comparative Example 1 described above. In the determination, as shown in FIG. 3A, the solder pastes A3 to C3 of Examples 2 to 4 and the solder paste D3 of Comparative Example 1 were
It was applied onto the land by printing or the like, and was passed through a reflow furnace. Then, after passing the furnace, it was visually observed whether or not a solder ball was generated on the Cu land around the solder as shown in FIG. 3B.

FIG. 4 is a diagram showing the solder ball generation rates (%) of Examples 2 to 4 and Comparative Example 1. In the figure, the horizontal axis represents the flat solder content (wt%), and the vertical axis represents the solder ball generation rate (%). The plot points of the flat solder particle content (wt%) on the horizontal axis are 25 wt%, 50 wt%, 75 wt%, and 100 w
4% of t%. The solder ball generation rate is obtained by preparing 100 samples for each content of the flat solder particles in each of the solder pastes A3 to B3, and expressing the number of solder balls generated by%.

The curve L11 has a maximum diameter Dm of 30 μm or more and 4
Solder powder A consisting of flat solder particles less than 5 μm
1, the curve L12 represents the solder ball generation rate when using the solder powder B1 composed of the flat solder particles having a maximum diameter Dm of 45 μm or more and less than 65 μm, and the curve L13 represents the maximum diameter. This is the solder ball generation rate when the solder powder C1 composed of the flat solder particles having a Dm of 65 μm or more and 80 μm or less is used.

As shown in FIG. 4, only spherical solder particles having a particle diameter of 20 to 30 μm (spherical solder particles of 100 wt.
%), And the solder ball generation probability is 100% in Comparative Example 1 using the solder paste D3 in which a thermoplastic rosin flux is added to the solder powder.
It is.

On the other hand, in the case of the solder paste A3 of Example 2 using the solder powder A1 composed of the flat solder particles having a maximum diameter Dm of 30 μm or more and less than 45 μm,
As shown by the curve L11, the flat solder particle content (w
t%) is 25 wt%, 50 wt%, 75 wt% and 1 wt%
As the content increases, such as 00 wt%, the solder ball generation rate decreases. Flat solder particle content (wt%) is 7
In the range of 5 to 100 wt%, the solder ball generation rate decreases to about 80%.

Next, the maximum diameter Dm is not less than 45 μm and not more than 65 μm.
Powder B comprising a group of flat solder particles in a range of less than
In the case of the solder paste B3 of Example 3 using No. 1, as shown by the curve L12, a more excellent solder ball suppressing action can be obtained than in the case of the curve L11. In particular,
In the vicinity of the flat solder particle content of 25 wt%, the solder ball generation rate already drops to about 80%. When the flat solder particle content exceeds 25 wt%, the solder ball generation rate further decreases, and when the content is 50 wt% or more, about 70%
It drops to around.

In the case of the solder paste C3 of Example 4 using the solder powder C1 composed of a group of flat solder particles having a maximum diameter Dm of not less than 65 μm and not more than 80 μm, as shown by a curve L13, the solder powders A1 and B1 are used. Curve L11,
An even better solder ball suppressing effect can be obtained than in the case of L12. Specifically, the flat solder particle content 25
In the vicinity of wt%, the solder ball generation rate decreases to about 70%, and when the content is 50 wt% or more, it decreases to about 35 to 50%. In particular, the flat solder particle content is 75 wt.
% And the spherical solder particles 25 wt%, the solder ball generation rate shows the lowest value of about 35%.

It is presumed that the use of solder powder containing flat solder particles avoids the generation of solder balls because the flat solder particles are less likely to aggregate together when melted by heating such as reflow. In addition, when the flat solder particles coexist with the amorphous or spherical solder particles, the flat solder particles bridge between the amorphous or spherical solder particles and cause the agglomeration of the amorphous or spherical solder particles. It is presumed that it will prevent.

Referring to FIG. 4, the curves L11 to L13
In any case, the content of the flat solder particles in the solder powder is 2% by weight based on the total weight of the solder powder.
It turns out that 5 wt% or more is preferable. If it is less than 25 wt%, the solder ball generation rate will be 80% or more. Further, when the content of the flat solder particles is set to 100 wt% and the entire solder powder is occupied by the flat solder particles, extremely good results can be obtained.

<Example 5> In Example 1, the solder powder having the lowest solder ball generation rate and the compounding ratio, that is, the solder powder C1 composed of flat solder particles having a maximum diameter Dm of 65 μm to 80 μm were used. In the case of a flat solder particle content of 75 wt% and a spherical solder particle content of 25 wt%, a solder paste was prepared for each flux content, and the relationship between the flux content and the solder ball generation rate was determined. Examined.

FIG. 5 is data showing the relationship between the flux content and the solder ball generation rate. A curve L21 indicates the solder ball generation rate when the conventional solder paste is used, and a curve L21 indicates the solder ball generation rate when the solder paste according to the present invention is used. Referring to FIG. 5, it is understood that the content of the solder flux is preferably in a range of 5 wt% to 45 wt%. In particular, an excellent solder ball suppression effect can be obtained at 10 wt% to 35 wt%. If the solder flux content exceeds 45% by weight, the effect of suppressing solder balls is lost.

In soldering the components, the solder paste according to the present invention is applied on one surface of the component mounting board, and then the components are placed on the solder paste and heat-treated. Thereby, components can be soldered while avoiding generation of solder balls.

In the solder paste according to the present invention, various types of conventionally known fluxes can be used. The main function of the flux is to remove the oxide film on the surface of the metal conductor provided on the component mounting board and the metal for soldering the component, thereby improving the wettability of the solder. As the flux, those containing rosin as a main component are best known. Rosin contains a carboxylic acid such as abietic acid and levobimaric acid, and the function of a carboxyl group removes an oxide film on a metal surface to be soldered. In the solder paste according to the present invention, such a rosin-based flux can be used.

The flux generally contains a solvent, in addition to the rosin described above, for the purpose of improving printability and obtaining temporary fixing strength.
Various additives such as a plasticizer or a thixotropic agent are blended.
For example, Japanese Patent Application Laid-Open No. 11-121915 discloses that
A type of flux that is adjusted by adding alcohol is disclosed. Such a technique can be applied to the solder paste according to the present invention.

Further, as another flux, an RMA (halogen-free) flux defined by the mill standard is also known. In the case of this flux, after reflow
The step of cleaning flux and the like is omitted. In the present invention, such a flux can also be used.

Further, as a special example, an adhesive flux containing an adhesive resin and a curing agent can be used. Since this adhesive flux contains an adhesive resin and a curing agent, after soldering, the adhesive resin can function as an adhesive for fixing the component mounting board and the component. For this reason, it is possible to prevent the components from peeling or falling off due to impact or thermal stress, and to improve the reliability of the solder joint. This point is significantly different from the conventional rosin flux having no bonding function after soldering.

Further, according to the adhesive flux, a sufficient fixing strength can be ensured even without a fillet portion. For this reason, it is not necessary to provide a region for generating a fillet portion in the component connection conductor (land) formed on the component mounting board, so that the mounting density can be improved.

As the adhesive resin contained in the adhesive flux, a resin having a high adhesive strength can be selected from a large number of resin materials in accordance with the temperature, and can be used as the adhesive resin. Therefore, after the components are soldered on the first side of the component mounting board of the double-sided mounting type using a solder paste containing an adhesive flux, the component mounting board 2
Even when a normal eutectic solder is used for the surface and the reflow furnace is used, the components mounted on the first surface do not cause problems such as shifting, Manhattan phenomenon (part standing phenomenon) or falling off. Of course, in both the first and second soldering processes, a solder paste containing an adhesive flux can be used.

In the adhesive flux, a preferred adhesive resin is a thermosetting resin. Specific examples of the thermosetting resin include at least one selected from an epoxy resin, a phenol resin, a polyimide resin, a silicone resin, a modified resin, and an acrylic resin.
The types and amounts of the exemplified resin materials can be selected according to the bonding temperature range, the target film hardness, and the like.

The curing agent contained in the adhesive flux may be any as long as it cures the adhesive resin. Preferably,
Contains carboxylic acids. The curing agent containing a carboxylic acid has not only a hardening action on the thermosetting resin but also a flux action for removing an oxide film on the surface of the metal to be soldered.

The adhesive flux may contain a solvent, a plasticizer, a thixotropic agent and the like. The solvent is added to adjust the curing temperature and the curing speed of the adhesive resin and to adjust the viscosity according to the application form. Plasticizers and thixotropic agents are also added to adjust the viscosity depending on the form of application. The amounts of the solvent, plasticizer, thixotropic agent and the like are selected according to the purpose of use.

Next, solder pastes using the above-mentioned adhesive flux were used in Examples 6 to 9 and Comparative Example 2,
3 will be described. Throughout Examples 6 to 9, as the solder powder, the solder powder having the lowest solder ball generation rate and the compounding ratio, that is, the maximum diameter Dm was 65 μm or more and 8 or more.
A solder powder composed of a group of flat solder particles having a particle size of 0 μm or less was used, and the compounding ratio of the flat solder particles was 75 wt% and the spherical solder particles was 25 wt%. However, it goes without saying that the solder powder shown in the first embodiment may be used.

Example 6 Bisphenol A was used as a thermosetting resin, and a carboxylic acid anhydride was used as a curing agent. The mixing ratio of the thermosetting resin and the curing agent is 1: 1:
It was set to 1. In addition, a small amount of a solvent and a thixotropic agent were blended to ensure viscosity.

The adhesive flux and the solder powder were mixed to prepare a solder paste. The mixing amount of the flux with respect to the solder powder was 10 wt%.

Using this solder paste, a chip component was soldered on a component mounting board. FIG.
(C) is a partial sectional view showing details of the component mounting board and a step of soldering the chip component to the component mounting board.
The component mounting board 1 includes a Cu film 51 (52) and a Ni film 61.
(62) and two lands formed by sequentially laminating the Au film 71 (72).

On the land of the component mounting board 1 described above,
The solder paste 81 (82) according to the present invention was applied (see FIG. 6A). When applying the solder paste 81 (82), printing was performed using a metal mask having a thickness of 100 μm. The opening size of the metal mask is 0.5mm x
0.3 mm, which is the same as the land size on which the electronic component 4 is mounted.

Then, the electronic component 4 having a length of 1 mm and a width of 0.5 mm is mounted on the solder paste 81 (82) (see FIG. 6B), and is passed through a reflow furnace.
The electronic component 4 was soldered on the component mounting board 1 (FIG. 6).
(C)). Thereafter, the lateral pressing strength was measured. FIG.
In (c), reference numeral 3 denotes a solder paste 81.
The flux according to the present invention included in (82) is shown, and becomes a fillet shape outside the end electrodes 41 and 42.

Comparative Example 2 For comparison, a chip component was soldered to a component mounting board using a conventional solder paste containing a rosin-based flux. The blending amount of the rosin flux with respect to the solder powder was 10 wt%.

FIGS. 7A to 7C are partial cross-sectional views showing details of the component mounting board and a step of soldering the chip component to the component mounting board. As illustrated, the component mounting board 1 has two lands in which a Cu film 51 (52), a Ni film 61 (62), and an Au film 71 (72) are sequentially stacked. A solder paste 91 (92) containing a rosin-based flux was applied onto the lands of the component mounting board 1 (see FIG. 7A).

Then, on the solder paste 91 (92) containing the rosin-based flux, a length of 1 mm and a width of 0.1 mm were applied.
The electronic component 4 of 5 mm was mounted (see FIG. 7B) and passed through a reflow furnace to solder the electronic component 4 onto the component mounting board 1 (see FIG. 7C). After this,
The lateral pressing strength of the part was measured.

FIG. 8 is a view showing the results of a lateral pressing strength test of the components of Example 6 and Comparative Example 2. As shown in the figure, the average value of the lateral pressing strength of Comparative Example 2 was about 600 g,
In Example 6, an average strength of about 1500 g could be obtained.

Example 7 The adhesive flux prepared in Example 6 was mixed with a solder powder to prepare a solder paste. The amount of the adhesive flux to the solder powder was increased to 20 to 35 wt%.

Using this solder paste, the electronic component 4 was mounted on the component mounting board 1 and soldered according to FIG. More specifically, referring to FIG. 9, the component mounting board 1 includes a Cu film 51 (52), a Ni film 61 (62),
It has two lands formed by sequentially laminating u films 71 (72) (see FIG. 9A).

On the land of the component mounting board 1 described above,
The solder paste 81 (82) according to the present invention was applied (see FIG. 9A). When applying the solder paste 81 (82), printing was performed using a metal mask having a thickness of 100 μm. The opening size of the metal mask is 0.5mm x
0.3 mm, which is the same as the land size on which the electronic component 4 is mounted.

Then, the electronic component 4 having a length of 1 mm and a width of 0.5 mm is mounted on the solder paste 81 (82) (see FIG. 9B), and is passed through a reflow furnace.
The electronic component 4 was soldered onto the component mounting board 1 (FIG. 9).
(C)).

The appearance after soldering is as shown in FIG. FIG. 10 is a sectional view taken along line 10-10 of FIG. 9C. In the seventh embodiment, a solder paste whose flux content is intentionally increased is used. However, the solder amount is substantially small, and the electronic component 4 is inclined as shown in FIG. No, it was soldered in normal condition. In FIG. 9 (c) and FIG.
Indicates an adhesive flux contained in the solder paste 81 (82), and becomes a fillet shape outside the end electrodes 41 and 42.

Further, by using the solder paste containing the adhesive flux, the periphery of the electronic component 4 after soldering was covered with the adhesive flux, and the improvement of the lateral pressing strength of the component was also recognized. In this way, by intentionally increasing the adhesive flux content in the solder paste, the thickness of the solder can be controlled by the solder paste. Particularly, the content of the adhesive flux is 35 wt%.
In the above region, oblique soldering was avoided, and a bonding strength equal to or higher than that of the conventional product was obtained.

Comparative Example 3 For comparison, an electronic component 4 was mounted on the component mounting board 1 and soldered according to FIG. 11 using a conventional rosin-based flux-containing solder paste. Specifically, referring to FIG. 11, the component mounting board 1 includes two lands formed by sequentially laminating a Cu film 51 (52), a Ni film 61 (62), and an Au film 71 (72). (See FIG. 11A).

On the land of the component mounting board 1 described above,
Rosin flux-containing solder paste 91 (92)
Was applied (see FIG. 11A). Solder paste 91
In the application of (92), printing was performed using a metal mask having a thickness of 100 μm. The opening size of the metal mask was 0.5 mm × 0.3 mm, and was the same as the land size on which the electronic component 4 was mounted.

Then, the electronic component 4 having a length of 1 mm and a width of 0.5 mm is mounted on the solder paste 91 (92) (see FIG. 11 (b)) and passed through a reflow furnace to obtain the electronic component. 4 was soldered onto the component mounting board 1 (see FIG. 11C).

The appearance after reflow soldering is as shown in FIG. FIG. 12 is a partial cross-sectional view taken along line 12-12 of FIG. As shown in FIG. 12, in the case of soldering with the conventional rosin-based flux-containing solder paste, the amount of solder was too large, and the electronic component 4 was obliquely soldered. 11C and FIG. 12, reference numeral 93 indicates a rosin-based flux contained in the solder paste 91 (92).

Example 8 A solder paste was prepared by mixing the adhesive flux prepared in Example 6 with a solder powder. As the solder powder, Sn (96.5) Ag
(3.5) was used. Adhesive flux content is 25
wt%. This is Example 8.

FIG. 13 shows the reflow temperature and the lateral pressing strength of the case where the chip parts were soldered using the solder paste of Example 8 and the case where the chip parts were soldered using the conventional rosin-based solder paste. FIG. In the drawing, a curve L1 shows the characteristics when the solder paste of Example 8 is used, and a curve L2 shows the characteristics when the conventional rosin-based solder paste is used.

As shown in FIG. 13, the solder paste containing the adhesive flux has a higher bonding strength than the conventional rosin-based solder paste in the reflow temperature range of 220 to 260 ° C. Especially, the reflow temperature is 230 ℃
As described above, a high bonding strength could be secured.

<Embodiment 9> Using the solder paste shown in Embodiment 8, a chip component was soldered to a component mounting board, and the bondability between the component mounting board and the terminal electrode of the chip component was observed. The solder paste containing the flux had the same bonding properties as the rosin-based solder paste. By the way, when the conventional conductive adhesive and anisotropic conductive paste were evaluated in the same manner as the above-mentioned flux, joining of the component mounting board and the terminal of the component was not obtained.

In the above embodiment, the electronic component 4 is mounted on one surface of the component mounting board 1, but the electronic component 4 can be mounted on both surfaces of the component mounting board 1. in this case,
After performing a soldering process using the solder paste according to the present invention on one surface of the component mounting board 1, the component mounting board 1
On the other side, the electronic component 4 can be soldered using a solder different from the solder paste according to the present invention, for example, a conventional rosin-based solder paste. Alternatively, the electronic component 4 can be soldered on both sides of the component mounting board 1 using the solder paste according to the present invention. In any case, the electronic component 4 does not cause a problem such as shifting, a Manhattan phenomenon (component standing phenomenon), or falling off.

[0083]

As described above, according to the present invention, it is possible to provide a solder paste and a soldering method capable of avoiding generation of solder balls.

[Brief description of the drawings]

FIG. 1 is a view schematically showing flat solder particles contained in a solder paste according to the present invention.

FIG. 2 is a diagram schematically showing a composition of a solder paste containing the flat solder particles shown in FIG. 1 and solder particles having other shapes.

FIG. 3 is a diagram showing a method for determining the occurrence of solder balls.

FIG. 4 is a view showing a solder ball generation rate (%) of Examples 2 to 4 and Comparative Example 1.

FIG. 5 is data showing a relationship between a flux content and a solder ball generation rate.

FIG. 6 is a partial cross-sectional view showing details of a component mounting board and a step of soldering a chip component to the component mounting board when a solder paste containing a flux according to the present invention is used.

FIG. 7 shows details of a component mounting board when a conventional solder paste containing a rosin-based flux is used;
It is a fragmentary sectional view showing the soldering process of a chip part to a parts mounting board.

FIG. 8 is a diagram showing the results of a component lateral pressing strength test for the soldering method according to the present invention shown in FIG. 4 and the conventional soldering method shown in FIG.

FIG. 9 is a partial cross-sectional view showing a soldering method using a solder paste containing a flux according to the present invention.

FIG. 10 is a view showing an appearance when a chip component is soldered on a component mounting board by the soldering method according to the present invention shown in FIG. 9, and a portion along a line 10-10 in FIG. 9; It is sectional drawing.

FIG. 11 is a partial cross-sectional view illustrating a conventional soldering method using a rosin-based flux-containing solder paste.

12 is a view showing an appearance when a chip component is soldered on a component mounting board by the conventional soldering method shown in FIG. 11, and is a partial cross-sectional view along line 12-12 in FIG. 11; It is.

FIG. 13 is a graph showing the relationship between the reflow temperature and the component lateral pressing strength when a chip component is soldered using the solder paste according to the present invention and when a chip component is soldered using a conventional rosin-based flux-containing solder paste. It is a figure showing a relation.

[Explanation of symbols]

 110 Flat solder particles 120 Irregular or spherical solder particles 130 Flux 1 Component mounting board 3 Flux 4 Chip components 81, 82 Solder paste

Claims (15)

[Claims] 1. A solder paste containing solder powder, wherein the solder powder contains flat solder particles. 2. The solder paste according to claim 1, wherein the content of the flat solder particles is 25% by weight to 100% by weight based on the total weight of the solder powder. 3. The solder paste according to claim 1, wherein the solder powder contains spherical solder particles. 4. The solder paste according to claim 3, wherein the flat solder particles and the spherical solder particles have substantially the same weight. 5. The solder paste according to claim 1, wherein a ratio (Dm / t) of a maximum diameter Dm to a thickness t of the flat solder particles is 1.5 ≦ 1.5. Solder paste in the range of (Dm / t) ≦ 16. 6. The solder paste according to claim 1, wherein the flat solder particles have a maximum diameter Dm of 30 μm to 45 μm.
m, and the thickness t is in the range of 10 to 20 μm, and the maximum diameter Dm is 45 μm or more and less than 65 μm.
Are in the range of 7 to 14 μm, and the maximum diameter Dm is 65 μm to 80 μm and the thickness t is 5 μm to 10 μm.
Solder paste containing at least one kind of particles in the range. 7. The solder paste according to claim 1, wherein the solder paste contains a solder flux. 8. The solder paste according to claim 7, wherein the content of the solder flux is 5 wt% to 45 wt%.
% Solder paste in the range of%. 9. The solder paste according to claim 7, wherein the solder flux contains an adhesive resin and a curing agent. 10. The flux according to claim 9, wherein the adhesive resin includes a thermosetting resin. 11. The solder paste according to claim 10, wherein the thermosetting resin is an epoxy resin, a phenol resin,
A solder paste containing at least one selected from a polyimide resin, a silicon resin, a modified resin, and an acrylic resin. 12. The flux according to claim 9, wherein the curing agent contains a carboxylic acid. 13. The solder paste according to claim 1, wherein the solder powder is composed of Sn, Cu, Ag, Sb, Pb, and I.
a solder paste containing at least one selected from n and Bi. 14. A soldering method using the solder paste according to claim 1. 15. The method according to claim 14, wherein the electronic component is soldered on the component mounting board.