JP2975114B2 - Solder deposition composition and mounting method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a composition for solder deposition and a mounting method using the same, and more particularly, to forming a uniform and relatively large film thickness on a conductive portion (pad) of a circuit board. The present invention relates to a solder deposition composition that can form a solder layer in a short period of time and can precoat solder without causing a solder bridge even when the interval between conductive portions is narrow, and a mounting method using the same.

(Prior art) The conventional solder composition (solder paste) used in the surface mounting technology disperses a solder powder, which is an alloy of Sn and Pb, in a flux, and further mixes necessary additives. In the form of a paste.

When mounting an element on a substrate using a conventional solder composition, first, the solder composition is supplied to a pad, which is a joint on the substrate, and the element is mounted so that the terminal of the element is located on the solder composition. By mounting and heating in this state, the solder composition is melted and the element and the pad are electrically connected.

In such a mounting, if the space between the pads is sufficiently ensured, the element and the pad can be electrically connected without any problem. When supplying or melting an object, the solder may be connected to form a solder bridge. When a solder bridge is formed, a short circuit occurs in the circuit, deteriorating the function of the circuit. Also, repairing the solder bridge requires a great deal of cost, which is a major problem.

As a solder deposition composition that solves these problems, US
P5,145,532 (JP-A-1-157796) discloses a solder deposition composition containing a metal Sn powder and an organic acid lead salt.

The solder deposition mechanism of the composition for solder deposition is considered as follows.

1) The organic acid lead salt is dissociated into organic acid ions and lead ions by heating.

2) Pb ions are substituted and reduced to metal Pb due to the coexistence of metal Sn having a large ionization tendency, and metal Sn is oxidized to Sn ions.

3) The reduced metal Pb is diffused into the metal Sn excessively present in the composition, and solder is formed.

It has been found that this solder deposition process behaves significantly differently from the case where a conventional solder composition (solder paste) melts at a temperature below the melting point of the solder. For example, when pre-coating solder on a pad of a printed wiring board, in the conventional solder composition, unless an appropriate amount of solder paste corresponding to the pad area is supplied on the pad, the solder supplied when heat is applied The paste is dripping,
Adjacent solders are connected to form a solder bridge. On the other hand, the solder deposition composition does not need to be supplied by printing using a mask corresponding to the pad pattern, and even if supplied by so-called solid coating, only the conductive pad is pre-coated with solder and the solder bridge is formed. Some features do not occur. In recent years, it has become very difficult to supply solder compositions by printing so that solder bridges do not occur in high-density printed wiring boards accompanying the miniaturization of electronic equipment, and USP 5,145,532 However, it is getting in the spotlight. However, in this composition for solder deposition, the above-described solder deposition mechanism occurs on individual Sn particles.In the case of Sn powder having a certain particle size distribution industrially, the smaller the particle size, the higher the surface area ratio, the smaller the reaction. It has been found that the progress of the reaction is faster, and that the larger the particle size, the slower the progress of the reaction. As a result, USP 5,145,532
In the composition for solder deposition described above, the composition of the final target solder varies, making it difficult to obtain a uniform solder precoat. It is considered that the use of Sn powder having a uniform particle size also makes the progress of the reaction uniform, but preparing such a Sn powder is too uneconomical.

Further, when only the substitution reaction between the metal Sn powder and the Pb ion of the organic acid lead salt is changed to the Sn63% -Pb37% alloy, the metal Sn that is subjected only to the ion exchange reaction without finally becoming a solder alloy is used. There is also a disadvantage that the content of the organic acid lead salt in the composition for solder deposition becomes high, and the amount of the active ingredient in the composition for solder deposition decreases.

In recent years, in soldering of an electronic part, a solder composition is supplied onto a pad of a printed wiring board by printing, an electronic component is mounted on the solder composition, and the solder composition is re-melted (reflowed). In addition to the conventional method of soldering the lead, the pad on the board is pre-coated with solder in advance, the flux is supplied on it, the electronic components are mounted, and the pre-coated solder is re-melted by heating Then, a method of soldering a lead portion of a component is performed.
When mounting LSI electronic components with a large number of leads using this method, for example, QFP (Quad Flat Package), in order to securely solder each lead to each pad on the same plane on the board , The flatness between the leads (Le
It is necessary to perform solder pre-coating so as to have a sufficient height (thickness) to absorb variations in ad coplanality.

However, in USP 5,145,532 solder deposition composition,
When a large amount of solder is pre-coated on a pad of a printed wiring board, it is necessary to use a thick mask for which printing control is difficult in order to supply a solder deposition composition by a printing method which is a general method. In addition, even when the composition for solder deposition is supplied thickly, the composition for solder deposition will drop during heating,
As a result, a large amount of solder is not pre-coated on the pad,
It is necessary to supply the composition for solder deposition repeatedly to cause the substitution reaction.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and enables a solder layer having a uniform and relatively large film thickness to be formed on a pad in a short time, and furthermore, a conductive portion is provided. It is an object of the present invention to provide a solder deposition composition that can perform solder precoating without causing a solder bridge even when the interval is small.

(Means for Solving the Problems) The present invention relates to a Sn—Pb alloy powder 10 having a Sn content of 90 to 65% by weight.
9090% by weight and an organic acid lead salt of 7.5-50% by weight as essential components, wherein Sn of the alloy powder and Pb of the organic acid lead salt are contained.
Provided is a solder depositing composition for depositing solder by a substitution reaction with ions.

In addition, the present invention provides a solder deposition composition containing 10 to 90% by weight of an Sn-Pb alloy powder having a Sn content of 90 to 65% by weight, and 7.5 to 50% by weight of an organic acid lead salt as essential components. The step of supplying to the conductive portion formed on, and heating the solder deposition composition supplied on the conductive portion to a temperature higher than the solidus in the phase diagram of the solder, the Sn-Pb alloy powder A step of depositing solder by a substitution reaction between Sn and Pb ions of the organic acid lead salt to form a solder precoat, a step of mounting an element on the solder precoat, and melting the solder precoat Performing the element on the conductive portion.

(Embodiment of the invention) The composition for solder deposition of the present invention is characterized by containing a Sn-Pb alloy powder and a lead salt of an organic acid.

In the composition for solder deposition, on the surface of the Sn-Pb alloy powder dispersed in the composition, the element having a large ionization tendency (Sn) in the Sn-Pb alloy powder and Pb of the organic acid lead salt are mixed. The ion exchange reaction proceeds. That is, a part of Sn is ionized and Pb ions of the organic acid lead become Pb. The collision between the Pb obtained in this way and the Sn-Pb alloy
Pb is further alloyed with the Sn-Pb alloy. As Pb is alloyed, the amount of Pb contained in the Sn—Pb alloy gradually increases from the Sn-rich state. For this reason, the melting point of the Sn—Pb alloy is lowered and melted from the surface, forming a solder layer on the pad. On the pad surface, the solder deposited by the flux action by the action of the activator in the solder deposition composition wets the pad.

The mechanism of solder deposition in the present invention is based on alloying at the atomic level, and in the composition for solder deposition,
The reaction between the Sn-Pb alloy particles and the organic acid lead salt occurs uniformly.
Therefore, the Sn—Pb alloy particles do not agglomerate at one time to form large agglomerated particles, and gradually adhere to the pad surface while maintaining the dispersed state in the solder deposition composition. As a result, a solder layer can be formed without forming a solder bridge. Since the present invention has such a mechanism, it is considered that even when the pad interval is small, the solder layer is appropriately formed following the pad with the small interval, and the occurrence of the solder bridge is greatly reduced.

In the above mechanism, solder deposition (alloying reaction)
Is governed by the opportunity for atomic-level collisions of Sn and Pb. Since the alloy powder is used in the composition for solder deposition of the present invention, the reaction time for the solder deposition to reach the final target solder composition is shortened. That is, when an alloy powder is used, the solder precipitation does not depend only on the collision between the metal powder and the metal obtained by the ion exchange reaction. The amount of the substituted metal obtained can be reduced. That is, by using the alloy powder, the amount of the substitution metal obtained by the substitution reaction can be reduced, so that the content of the metal in the solder deposition composition can be increased, and the thickness of the film can be easily increased. A solder layer can be formed. Further, the variation in the composition of the solder can be minimized because the variation in the composition of the used alloy powder is almost reflected.

Further, by using the alloy powder, the ratio of the metal in the composition for solder deposition can be increased, and the amount of the effective component for forming the solder layer on the conductive portion of the substrate can be increased. In the case of the composition for solder deposition disclosed in USP 5,145,532, in order to make the Sn-Pb eutectic composition from only metal Sn, a composition for solder deposition of Sn powder and an organic acid lead salt used only for ion exchange reaction Since the proportion in the product is large, that is, because the amount of the active component that becomes the solder in the solder deposition composition is small, when forming a large amount of solder on the pad, when supplying the solder deposition composition by printing A thick mask is required.

In this case, it is difficult to control the coating thickness of the composition for solder deposition, and the efficiency of cleaning in a post-process is deteriorated. Further, even when the composition for solder deposition is supplied thickly, the composition is dropped due to heating and is not precoated just because it is supplied. That is, there is a limit to the amount of solder pre-coated on the pad. For this reason, when it is desired to precoat thickly, supply of a composition for solder deposition,
It is necessary to repeat the steps of reaction and washing, which is very inefficient.

However, when the composition for solder deposition of the present invention is used, since the amount of the effective component (effective metal content) is large, a relatively thin mask that can easily control the coating film thickness can be used, and the post-process The load of cleaning is small, even if you want to precoat thickly, supply, reaction,
The washing step is only required once.

Here, in the present invention, as the Sn—Pb alloy, when the final target solder composition is Sn—Pb eutectic (Sn / Pb = 63/37),
A Sn-Pb alloy powder whose Sn / Pb content is higher than 63/37 is used. Note that a small amount of metal, for example, Ag or Cu may be contained in the Sn-Pb alloy.

In the present invention, the particle size of the alloy powder, 1 ~ 20μ
m is preferable. This is because the particle size of the alloy powder is 1
If the thickness is less than μm, the amount of solder that oxidizes and precipitates on the alloy surface will be insufficient, and if it exceeds 20 μm, the variation in the amount of solder deposited will increase.

In the present invention, the compounding amount of the alloy powder in the solder deposition composition is preferably from 10 to 90% by weight. this is,
If the amount of the alloy powder is less than 10% by weight, the amount of solder to be deposited becomes insufficient. If the amount exceeds 90% by weight, it becomes difficult for the solder deposition composition to maintain a paste state. A particularly preferred amount is 20 to 70% by weight.

Examples of the organic acid constituting the organic acid lead salt include rosin and derivatives thereof; aliphatic carboxylic acids such as stearic acid, oleic acid, neodecanoic acid, sebacic acid, and fumaric acid; benzoic acid, phthalic acid, isophthalic acid, and tricarboxylic acid. Aromatic carboxylic acids such as melitic acid and pyromellitic acid; naphthenic acid and the like can be used. In addition to monobasic acids,
It is also possible to use dibasic or tribasic or higher polybasic acids.

In the composition for solder deposition of the present invention, as an organic acid,
In particular, it is preferable to use rosin or a derivative thereof or naphthenic acid. As the rosin, it is possible to use pure substances such as gum rosin, tall oil rosin, and wood rosin, as well as abietic acid and pimaric acid, which are the main components of these rosins. In addition, as such rosin derivatives, disproportionated rosin, hydrogenated rosin, maleated or fumarated rosin, and the like can also be used. The type of the organic acid lead salt is appropriately selected according to the solder precoat conditions (temperature, atmosphere, etc.).

In the composition for solder deposition of the present invention, by adding a small amount of an organic acid silver salt or an organic acid copper salt in addition to the organic acid lead salt,
Ag and Cu can be added as the third component in addition to Sn and Pb.

In the present invention, the compounding amount of the organic acid lead salt in the composition for solder deposition is 7.5 to 50% by weight (for example, in the case of lead naphthenate containing 20% of Pb, the lead content is 1.5 to 10%). Is preferred. If the amount of the organic acid lead salt is less than 7.5% by weight, the interfacial tension of the deposited solder is small, so that a solder bridge is likely to be formed. Becomes unstable and cannot be supplied accurately on the pad at the time of solder pre-coating.

The amount of Pb in the solder deposition composition that effectively exerts the effect of suppressing the occurrence of solder bridges differs depending on the alloy composition of the alloy powder used and the type of the organic acid lead salt. Further, by adjusting the amount of Pb in the organic acid lead salt, it is possible to cope with a solder precoat in a fine pattern.
For example, if the amount of Pb in the organic acid lead salt is too small, the pattern follow-up property decreases, so it is necessary to secure a certain amount of Pb.

In the composition for solder deposition of the present invention, an adhesive such as gum rosin, an activator such as diethanolamine or triethanolamine, or an activator such as butyl carbitol or mineral spirit may be used, if necessary, similarly to the conventional composition for solder deposition. Additives such as a viscosity modifier such as a solvent, caster wax and cellulose powder may be blended to form a paste. When the above additive is added to the composition for solder deposition, the additive may be added together with the alloy powder and the organic acid lead salt, and an adhesive, an activator, and a solvent are mixed in advance to prepare a flux. And a lead salt of an organic acid.

When solder is deposited using the composition for solder deposition of the present invention, it is necessary to set the heating temperature of the solder deposition reaction to a temperature higher than the solidus in the solder phase diagram. This is because, when the heating temperature at the time of solder deposition is set below the solidus, the diffusion of Pb reduced and precipitated from the organic acid lead salt and the alloy powder in the composition for solder deposition becomes solid-solid diffusion,
This is because the progress of the reaction becomes extremely slow, and it becomes difficult to obtain the final target solder composition. When the heating temperature is set to a temperature higher than the solidus, solid-liquid diffusion occurs, the reaction proceeds quickly, and the final target solder composition can be easily obtained. Specifically, the heating temperature is preferably from 210 to 220 ° C.

When mounting an electronic component on a conductive part of a printed wiring board using the composition for solder deposition of the present invention, first, a Sn-Pb alloy powder and a solder deposit containing an organic acid lead salt as essential components are used. The composition is supplied to the conductive part formed on the substrate, and the solder deposition composition supplied on the conductive part is heated to obtain Sn-Pb.
Solder is precipitated by a substitution reaction between Sn of the alloy powder and Pb ion of the organic acid lead salt to form a solder precoat, the element is placed on this solder precoat, and the solder precoat is melted to conduct the element. Implement on the department. When melting the solder precoat, heating is performed at a temperature equal to or higher than the melting point of the deposited solder precoat.

Hereinafter, Examples of the composition for solder deposition of the present invention will be specifically described.

(Example 1) First, paste flux A was prepared by mixing 60% by weight of gum rosin as an adhesive, 10% by weight of diethanolamine as an activator, 10% by weight of caster wax, and 20% by weight of butyl carbitol as a solvent. .

Next, a solder powder having an average particle size of 10 μm (Sn / Pb = 7
0/30), 20% by weight of lead naphthenate containing 24% by weight of Pb as an organic acid lead salt, and the flux A
Was mixed with 40% by weight to prepare a solder deposition composition of the present invention.

(Reference Example, Comparative Example 1) Alloy powder or Sn with the type and compounding amount shown in Table 1
Except for mixing the powder and the lead naphthenate, compositions for solder deposition of Reference Example and Comparative Example 1 were prepared in the same manner as in Example 1.

The composition for solder deposition of Example 1, Reference Example and Comparative Example 1 was applied at a thickness of 250 μm on a QFP pattern having a pitch of 0.3 mm and 160 pins formed on a substrate, and this was applied on a hot plate at a temperature of 250 ° C. And the composition was placed for 120 seconds to heat the solder deposition composition to deposit solder. As the QFP pattern, a pattern obtained by performing flash gold plating on Ni was used. After the substrate was washed with toluene, it was dissolved in the acid of the solder to form a sample solution, and the sample solution was subjected to atomic absorption analysis. Table 2 shows the results.

As can be seen from Table 2, in the solder deposition compositions of Example 1, Reference Example and Comparative Example 1, a solder having a composition close to the theoretical composition can be obtained by heat treatment at 250 ° C. This means that an ion exchange reaction (substitution reaction) has occurred in the composition for solder deposition, which is a mechanism of the present invention. In Table 2, the theoretical composition is the target composition of the solder to be deposited.

Next, for the solder deposition compositions of Example 1, Reference Example and Comparative Example 1, variations in the solder composition during solder precoating were examined. This variation in the solder composition is obtained by forming a solder layer on each of the 20 QFP patterns for each composition as described above,
The content of Sn was measured by atomic absorption analysis of each sample solution, and the difference between the maximum value and the minimum value of the measured values was calculated. Table 3 shows the results. Further, the number of bridges in 160 pins when the solder layer was formed on the QFP pattern was visually examined. The results are shown in Table 3.

Next, for the compositions for solder deposition of Example 1, Reference Example and Comparative Example 1, the time until the solder was deposited (processing time)
Was examined. The time until the solder is deposited is as follows: for each composition, a composition layer for solder deposition is formed on each of the four QFP patterns, and the heating time is 30 seconds.
60 seconds, 90 seconds, 120 seconds to form a solder layer, 20 sample solutions obtained from these solders were subjected to atomic absorption analysis to measure the Sn content, respectively, Sn content in the target composition The heating time was defined as the heating time when the amount became 90% or more based on the amount.
The results are shown in Table 3.

Next, with respect to the solder deposition compositions of Example 1, Reference Example and Comparative Example 1, the thickness of the formed solder was examined. For the thickness of the solder layer, a solder composition layer was formed with a thickness of 20 μm on the QFP pattern for each formation, and heated at 250 ° C. for 120 seconds to form a solder layer. It was determined by measuring with a surface roughness meter. The results are shown in Table 3.

As can be seen from Table 3, the compositions for solder deposition of Examples 1 and Reference Examples all have a small variation in the solder composition at the time of solder precoating, and the time until the solder is deposited is short.
The thickness of the solder layer that can be formed is large, and the number of solder bridges at the time of solder precoating is small. On the other hand, although the composition for solder deposition of Comparative Example 1 has a small number of solder bridges at the time of solder pre-coating, the variation in solder composition is large, and the time until solder deposition is long,
The thickness of the solder layer that can be formed was small.

(Examples 3 to 5, Comparative Example 2) Next, in order to clarify the effects of the present invention, the dispersion of the solder composition at the time of solder pre-coating, the time until the solder is deposited, and the thickness of the solder film are further described. I examined it in detail.

First, alloy powder or Sn powder and an organic acid metal salt were blended in the types and blending amounts shown in Table 4, and the flux A used in Example 1 was blended in the blending amounts shown in Table 4 to obtain the respective components. Was prepared.

With respect to each of the solder deposition compositions, the variation in the solder composition at the time of solder pre-coating, the time until the solder was deposited, and the thickness of the formed solder were examined. Table 5 shows the results of the variation in the solder composition, FIG. 6 shows the results of the time until the solder was deposited, and Table 6 shows the thickness of the formed solder. In addition, the variation of the solder composition at the time of solder pre-coating was examined in the same manner as in Example 1, and the time until the solder was deposited was examined by atomic absorption analysis for the Sn content when heated for several seconds each. Regarding the thickness of the solder film, 200 μm, 300 μm, 400 μm,
When the composition layer for solder deposition was formed at each thickness of 500 μm, the thickness of the formed solder layer was examined. The other points in these evaluations were the same as in Example 1.

As is clear from Table 5, the composition for solder deposition of the present invention containing the alloy powder can form a solder layer having a small variation in composition. In particular, those containing solder powder closer to the target composition had smaller composition variations. On the other hand, the composition for solder deposition containing a single metal powder had a large variation in the composition of the solder layer to be formed. Further, as is clear from the figure, it was found that the composition for solder deposition of the present invention including the alloy powder approaches the target composition in a short heating time. In particular, those containing solder powder closer to the target composition took shorter time. In contrast, the composition for solder deposition containing a single metal powder took a long time to approach the target composition.

Furthermore, as is clear from Table 6, the solder deposition composition of the present invention containing the alloy powder had a large thickness of the formed solder layer. In particular, the thickness containing solder powder closer to the target composition became larger. On the other hand, the composition for solder deposition containing a single metal powder had a small thickness of the formed solder layer. As can be seen from Table 6, in the composition for solder deposition of the present invention, as the thickness of the composition layer for solder deposition increases, the thickness of the solder layer increases. In the composition for solder deposition containing, even if the thickness of the composition layer for solder deposition is increased, the thickness of the solder layer does not increase so much. That is, it has been found that the solder deposition composition containing a single metal powder has a limit in the thickness of the formed solder layer.

Such an effect is that in the solder deposition composition of the present invention containing the alloy powder, the amount of the replacement metal obtained by the substitution reaction can be reduced, and the content of the metal in the solder deposition composition is increased. Can be done.

(Example 6) Next, a test was performed to clarify the range of the optimal lead content in the composition for solder deposition of the present invention.

First, 40.0% by weight of solder powder (Sn / Pb = 65/35) having an average particle size of 10 μm as alloy powder, 7.5% by weight of lead naphthenate as an organic acid lead salt, 25.0% by weight of rosin as an adhesive, 8.0% by weight of triethanolamine as activator and 19.5% by weight of mineral spirit as solvent
Was mixed to prepare a composition for solder deposition of the present invention.

(Examples 7, 8 and Comparative Examples 3 and 4) Except that lead naphthenate was blended in the amounts shown in Table 7, the solder deposition of Examples 7 and 8 and Comparative Examples 3 and 4 was performed in the same manner as in Example 6. A composition for use was prepared.

(Example 9) The same procedure as in Example 6 was carried out except that the blending amount of the solder powder (Sn / Pb = 65/35) was 20.0% by weight and lead naphthenate was blended in the blending amount shown in Table 4. The composition for solder deposition of Example 9 was produced.

Each of the compositions for solder deposition of Examples 6 to 9 and Comparative Examples 3 and 4 was screen-printed with a thickness of 300 μm on a substrate having a QFP pattern of 0.3 mm pitch and 150 pins, and subjected to a heat treatment at a temperature of 220 ° C. To deposit solder. These substrates were washed with toluene and dried to form a solder layer on the QFP pattern of the substrate.

Next, the occurrence of solder bridges between the QFP patterns was visually observed for the solder layers formed on the substrate using the respective solder deposition compositions. The results are shown in Table 7. In addition, the observation result of the solder layer
It is shown in the table.

As can be seen from Tables 7 and 8, when lead naphthenate was used as the organic acid lead salt, the lead content was 1.5%.
When the content is not less than% by weight, it is possible to prevent the occurrence of a solder bridge at the time of solder precoating of a fine pattern. Thus, depending on the alloy composition of the alloy powder to be used and the type of the organic acid lead salt, there is a range of the lead content that effectively exerts the effect of preventing the occurrence of solder blitch at the time of solder precoating of a fine pattern. I do.

Next, for the solder deposition compositions of Examples 6 to 9,
Variations in the solder composition at the time of solder pre-coating, the time until the solder was precipitated (processing time), the thickness of the solder formed, and the number of solder bridges at the time of solder pre-coating were examined in the same manner as described above. As a result, each of the solder deposition compositions of Examples 6 to 9 has a small variation in the solder composition at the time of solder pre-coating, a short time until the solder is deposited, and a thick solder layer that can be formed. Was something.

Examples 10 and 11 Example 10 was repeated in the same manner as in Example 6 except that lead stearate (Example 10) and lead acetate (Example 11) were used instead of lead naphthenate as the organic acid lead salt. , 11 solder deposition compositions were prepared. The amount of lead stearate and lead acetate was such that the Pb content in the solder deposition composition was 2.0% by weight.
It was adjusted to become.

Each of Examples 10 and 11 was screen-printed at a thickness of 300 μm on a substrate having a QFP pattern of 0.3 mm pitch and 160 pins, and was subjected to a heat treatment at a temperature of 220 ° C. to deposit solder. These substrates were washed with toluene and dried to form a solder layer on the pads of the substrate.

Next, for the solder layer formed on the substrate using each of the solder deposition compositions, the dispersion of the solder composition at the time of solder pre-coating, the time until the solder is deposited (processing time), the solder formation The film thickness and the number of solder bridges at the time of solder pre-coating were examined. As a result, the compositions for solder deposition of Examples 10 and 11 have a small variation in the solder composition at the time of solder pre-coating, a short time until the solder is deposited, and a thick solder layer that can be formed, Moreover, no solder bridge was generated.

(Effects of the Invention) As described above, the composition for solder deposition of the present invention is composed of Sn-
Since the Pb alloy powder and the organic acid lead salt are contained as essential components, a solder layer having a uniform and relatively large film thickness can be formed on the conductive portion in a short time, and when the pad interval is narrow, Can be pre-coated with solder without causing a solder bridge.

BRIEF DESCRIPTION OF THE DRAWINGS The drawing is a graph showing the relationship between the heating time and the amount of Sn in the deposited solder.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seishi Kumamoto 258 Hachigaike, Miyoshi-cho, Nishikamo-gun, Aichi Prefecture Kobayashi Heights 202 (72) Inventor Takahiro Fujiwara 17-35, Furukawa Electric Works 14-101 (72) Inventor Noriko Katayama 1-2-14 Aioimachi, Akashi City, Hyogo Prefecture (56) References JP-A-4-300088 (JP, A) JP-A-1-157796 (JP, A) Hei 2-310991 (JP, A) JP 2-56197 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 35/34 310 H05K 3/34 B23K 35/26 310 C22C 13/00

Claims (5)

(57) [Claims] 1. A Sn—Pb alloy powder 10 having a Sn content of 90 to 65% by weight.
9090% by weight and an organic acid lead salt of 7.5-50% by weight as essential components, wherein Sn of the alloy powder and Pb of the organic acid lead salt are contained.
A solder depositing composition for depositing solder by a substitution reaction with ions. 2. The composition for solder deposition according to claim 1, further comprising a solvent and a viscosity maintaining agent. 3. The solder deposition composition according to claim 1, wherein the content of the Sn—Pb alloy powder is 20 to 70% by weight. 4. A Sn—Pb alloy powder 10 having a Sn content of 90 to 65% by weight.
Supplying a composition for solder deposition containing, as essential components, 90 to 90% by weight and an organic acid lead salt of 7.5 to 50% by weight; A step of heating to a high temperature to deposit solder by a substitution reaction between Sn of the Sn-Pb alloy powder and Pb ions of the organic acid lead salt. 5. A Sn—Pb alloy powder 10 having a Sn content of 90 to 65% by weight.
Supplying a solder depositing composition containing, as essential components, 90 to 90% by weight and an organic acid lead salt 7.5 to 50% by weight to a conductive portion formed on a substrate; Heating the solder deposition composition to a temperature higher than the solidus in the solder phase diagram,
A step of depositing solder by a substitution reaction between Sn of Pb alloy powder and Pb ions of the organic acid lead salt to form a solder precoat; a step of mounting an element on the solder precoat; and Melting the element and mounting the element on the conductive portion.