JPS6333196A - Flux for cream solder - Google Patents

Abstract

PURPOSE:To improve the reliability in soldering and to prevent the generation of defective products by adding at least >=1 kinds of respectively specific arom. alcohols or chain alcohols to a flux as a solvent thereof. CONSTITUTION:>=1 kinds of the solvents which are >=1 kinds of only either of the arom. alcohols expressed by the formula I and the chain alcohol expressed by the formula II or are mixed with both thereof are used as the solvent of the flux for cream solder which consists essentially of a rosin resin and is added with an activator. All these alcohols have no hygroscopicity and have adequate b.p. Satisfactory insulation resistance, is therefore, assured and the generation of solder balls is suppressed at about 210 deg.C soldering temp. The reliability is soldering is improved and the generation of the solder balls is suppressed by the above-mentioned method; therefore, the generation of the defective products is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a cream solder flux used when soldering, for example, thousand-knob type components to a printed circuit board by a single reflow method. The present invention relates to improvements in the solvent contained in this type of flux.

[Summary of the invention]

The present invention aims to lower the reflow temperature by using an aromatic alcohol or a chain alcohol having 5 or more carbon atoms as a solvent for cream solder flux, and at the same time achieves insulation by the solvent contained in the residual flux. This is intended to suppress the decrease in resistance and reduce the occurrence of so-called solder poles.

[Conventional technology]

Traditionally, for example, solder particles and rosin have been used to make chip-type electronic components on printed circuit boards.

A widely used method is to use a cream solder mixed with a flux consisting of an activator, an agent, a solvent, etc., and perform reflow soldering.

In this case, the solvent contained in the above flux includes (al
It is required to dissolve the rosin resin and activator, which are the main components of the flux, (bl) For soldering, it must have an appropriate boiling point for the temperature, and FC+: It must absorb as little moisture as possible.

For example, if the above-mentioned solvent has poor solubility in the rosin resin, activator, etc., the activator separates, creating a locally high 4 degree area, which causes corrosion.

In addition, if the boiling point of the solvent is too high, the solvent will remain after soldering and the insulation resistance will decrease.On the other hand, if the boiling point of the solvent is too low, the solvent will sometimes boil during soldering and be included in the cream solder. This causes problems such as scattering of solder powder and the inability to obtain a proper solder joint.

Usually, the lower limit of the boiling point of the selected solvent is the melting point of the solder used.

Alternatively, if the moisture absorption of the 8 agents (used) is high, the solder surface will oxidize due to this absorption and moisture, and after soldering, the formation of solder balls (powdered solder that is not integrated and is in an isolated state) can be seen, resulting in short circuits. There is a risk that it may cause defects such as

Therefore, many studies have been made in various fields regarding the solvents used in this type of flux.
5-114497 discloses the use of ethylene glycol monophenyl ether as a solvent, and JP-A-56-154297 discloses the use of 2-methyl-2,4-
It is proposed to use pencundiol.

However, the ethylene glycol monophenyl ether has a high boiling point of approximately 245°C, and in the current situation where the number of electronic components with poor heat resistance is increasing, and the soldering temperature is often set at around 210°C, the solvent may be used even after soldering. It remains in the interior and causes a decrease in insulation resistance. In fact, when the inventor measured the insulation resistance using a comb-shaped electrode, it was 40°C.

The value after 72 hours at a relative humidity of 90% showed a fairly low value of 1XIO3Ω. (The value of this insulation resistance is at least about 1×10 IQΩ.) On the other hand, the above 2-methyl-2,4-bentanediol is
The boiling point is as low as 195°C, and although soldering does not cause problems in terms of insulation resistance even at low temperatures, cream solder is hygroscopic and if reflow is not performed immediately after printing, the powdered solder will oxidize and the solder will oxidize. The occurrence of poles becomes extremely frequent.

In the current production line, it takes a considerable amount of time for cream solder to print and flow, so it is difficult to suppress the occurrence of the solder poles described above.

[Problem that the invention seeks to solve]

As described above, currently no solvent has been provided that satisfies all of the above-mentioned requirements, and there is a need for further improvements in flux.

Therefore, the present invention was proposed in view of the conventional situation, and provides an optimal solvent for flux in terms of insulation resistance and hygroscopicity. The purpose of the present invention is to provide a flux for ream soldering that can secure resistance and suppress the generation of solder balls after soldering.

[Means for solving problems]

The inventors of the present invention have conducted extensive research to achieve this objective, and have come to the conclusion that aromatic alcohols or chain alcohols having 5 or more carbon atoms are optimal as solvents for this type of flux.

The present invention has been completed based on this knowledge, and uses the general formula % formula % (1) as a solvent in a cream solder flux made of a rosin resin as a main component and an activator added. , m in the formula represents an integer of 0 to 2) Aromatic alcohol represented by ゛ or general formula C11■2,14
10H...(rI) (where n in the formula represents an integer of 5 to 14) is characterized by the addition of at least one type of chain alcohol.

Here, the above-mentioned aromatic alcohol is one having a hydroxyl group at the end of an alkylene chain bonded to a phenyl group, and specifically benzyl alcohol, phenylethanol, and phenylpropanol can be used.

In maximum (1) above, if m exceeds 2, the melting point of the corresponding alcohol will become too high, making it difficult to mix with rosin resins, activators, etc., and making it impractical as a solvent.

In addition, both linear and branched chain alcohols can be used, and the position of the hydroxyl group is not limited to the terminal, but isomers in which the hydroxyl group is bonded to the side chain can also be used.

However, if the number of carbon atoms n in -C formula (II) is less than 5, a problem will occur in terms of hygroscopicity, and conversely, if the number of carbon atoms exceeds 14, the melting point of the corresponding alcohol will be lowered as with the aromatic alcohol above. It becomes too fragile and is no longer practical as a solvent.

In the present invention, one or more of these aromatic alcohols or chain alcohols is used as a flux solvent. In this case, one or more of aromatic alcohols and chain alcohols may be selected and used, or a mixture of the two may be used.

Furthermore, it is also possible to use it in combination with other solvents.

On the other hand, i-cosine resin, which is the main component of cream solder flux, contains natural rosin extracted from pine trees,
Water white rosin (ww rosin), which is obtained by refining this natural rosin, and chemically synthesized resins are also used. The content of this rosin resin in the flux is set in the range of 55 to 75%.

In addition to the above-mentioned rosin-based resin, an activator is added to the flux in order to actively remove oxides, dirt, etc. from the surfaces of the metals to be soldered. As an activator, a compound is used that reacts with heat and decomposes at high temperatures to liberate acid and decompose surface oxides and stains, such as organic amine hydrochloride such as aniline hydrochloride and cycloamine hydrochloride, and organic amine bromic acid. Salt etc. are used. The amount of this activator added is usually about 1 to 3 t% by weight.

The flux made of the above-mentioned solvent, rosin resin, and activator is a solder powder made of a tin-containing low-melting metal such as a tin-lead alloy, a tin-lead-silver alloy, a tin-lead-bismuth alloy, a tin-indium alloy, etc. In this case, a thixotropic agent may be added to adjust the viscosity of the resulting cream solder.

As such a chicken agent, hydrogenated castor oil, solid wax, etc. can be used, and the amount added is 2 to 10% by weight.
That's about it.

[Effect]

The aromatic alcohol or chain alcohol used as a flux solvent in the present invention is not hygroscopic and has an appropriate boiling point.

Therefore, insulation resistance is ensured even at a soldering temperature of about 210° C., and the generation of solder balls can be suppressed.

〔Example〕

Hereinafter, the present invention will be explained using specific examples, but the present invention is not limited to these examples.

First, the types of rosin resins shown in Table 1.

A flux was prepared by mixing the activator, chicken agent, and solvent.

(Left below) Next, powdered solder (63% Sn, balance Pb, melting point 183°C) was produced by the atomization method and had a particle size of 50 μm or less.
88% by weight and 12ffiffi% of various fluxes shown in Table 1 (Examples 1 to 6 and Comparative Examples 1 to 2) were mixed to create cream solder. In addition, since the boiling point of hexanol is as low as about 158°C, in Example 4, Sn
B'r solder (melting point 138°C) was used.

The resulting cream solder was evaluated for solder ball formation and insulation resistance using the following methods.

First, prepare a comb-shaped electrode printed circuit board (glass-epoxy resin board, thickness 0.8 mm) specified by Shiraki Industrial Standard Jl5-Z-3197, and apply each of the cream solders described above to the comb-shaped electrode of the board. It was printed in a comb-shaped pattern perpendicular to the .

After leaving this at room temperature for 4 hours, it was reflowed at 210° C., and the number of solder balls generated between the electrodes was counted. Here, the case where there were 10 or less solder balls with a particle size of 50 μm or more was defined as "small j".

Next, this printed circuit board was placed in a constant temperature and constant temperature bath at 40° C. and relative humidity of 90%, and after being left for 72 hours, the insulation resistance was measured in the constant temperature and constant humidity bath.

Table 2 shows the measurement results using the above measurement method.

Table 2 From this Table 2, it can be seen that in each example in which aromatic alcohol or chain alcohol having 5 or more carbon atoms was used as a solvent for cream solder FLA 2X, insulation resistance was ensured and solder poles were generated. It can be seen that this has been suppressed.

[Effects of the Invention] As is clear from the above explanation, in the present invention, aromatic alcohol or chain alcohol having 5 to 14 carbon atoms is used to condition the flux for cream solder. Even when soldering is performed at temperatures as low as ℃, the insulation resistance between the conductor patterns is maintained.
Highly reliable soldering becomes possible.

By making it possible to lower the soldering temperature in this way, it is now possible to solder electronic components with poor heat resistance all at once using the reflow method, which is practical in terms of productivity and workability. It can be said that the quality is high.

Furthermore, since the solvent used in the flux of the present invention has almost no hygroscopicity, the generation of solder poles due to oxidation of the solder is suppressed, and the occurrence of defects such as short circuits is also suppressed.

Claims (1)

[Claims] In the cream solder flux made of rosin resin as the main component and an activator added, there are general formulas, mathematical formulas, chemical formulas, tables, etc. as solvents (however, m in the formula is 0). ) or a chain alcohol represented by the general formula C_nH_2_n_+_tOH (where n represents an integer from 5 to 14). Flux for cream solder.