JP2001105180A - Soldering flux - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a soldering flux, solder paste and wire solder which are excellent in solderability as well as joined assemblies of circuit boards and electronic parts dealing with fine pitching and the diversification of parts. SOLUTION: Rosin having an acid value ranging from 150 to 250 and a softening point ranging from 120 to 200 deg.C is added to the flux.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering flux, and a solder paste, a thread solder,
Liquid flux for flow, and the solder paste,
The present invention relates to a joined product of a circuit board and an electronic component manufactured using a thread solder and a liquid flux.

[0002]

2. Description of the Related Art Solder pastes, thread solders, liquid fluxes for flow, and the like are used in the electronics industry for surface mounting electronic components. In recent years, in order to reduce the size of electronic products, fine pitch of circuit boards has been required. Fine pitch components, for example, 0.3 mm pitch QFP (Quad Flat Package) type LSI, and CSP (Chip Size)
Package) is increasing. For this reason, solder paste, thread solder, and the like are required to respond to fine pitch. In order to respond to such demands of the industry, the average particle size of the solder particles in the solder paste has been reduced, and the thickness of the thread solder has been reduced. The contact area with the flux increases, and the oxidation of the solder powder leaves problems in storage stability, solderability, and the like.
Recently, lead-free Pb-free solder has been recommended due to environmental issues, and development has been promoted to shift to Pb-free solder in response to this. Among them, Sn-Zn based solder, which is attracting attention as a particularly promising one, has even worse solderability than ordinary Sn-Pb based solder. This is because Zn is more easily oxidized than Pb.

[0003]

One of the causes of the decrease in solderability is that the solder metal is oxidized during the preheating stage of the solder paste, at the time of reflow, and at the time of melting of the solder metal. It may remain on the substrate or generate solder balls.

The present invention solves the above-mentioned problems, and provides a solder paste, a thread solder, and a liquid flux for flow which are excellent in solderability, and is adapted to a fine pitch, diversification of parts, etc. And a joint of electronic components.

[0005]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that the method of preventing the oxidation of the solder metal at the preheating stage of the solder paste, at the time of reflow, and at the time of melting of the solder metal. The properties of rosin in the flux are important, and by adding rosin in the flux having an appropriate acid value and softening point to the flux, the solder paste is preheated, reflowed, and melted. The present invention has been found that it is possible to suppress the oxidation reaction with the flux by maintaining the atmosphere in a reducing atmosphere and to suppress the reaction between the oxygen in the atmosphere and the solder metal. That is, the present invention provides [1] a soldering flux characterized by containing a rosin having an acid value in a range of 150 to 250 and a softening point in a range of 120 to 200 ° C., [2] a soldering flux having an acid value of 150 to 250. The soldering flux according to [3], [1] or [2], characterized by containing rosin having a softening point in the range of 120 to 200 ° C. in a range of 30 wt% or more based on the total amount of rosin in the soldering flux. [4] The solder paste according to [3], wherein the solder paste includes the soldering flux described above and a solder powder, [4] the solder paste according to [3], wherein the solder powder does not include lead.
[5] A liquid flux for flow prepared from the soldering flux according to [1] or [2], [6] [1]
Or a thread solder containing tin, comprising the soldering flux according to [2] and a solder alloy; [7]
The solder alloy according to [6], wherein the solder alloy does not contain lead, and the bonding of a circuit board and an electronic component manufactured using the solder paste according to [8], [3] or [4]. [9] A bonded product of a circuit board and an electronic component manufactured using the thread solder according to [9] [6] or [7], [1]
[0] A joined product of a circuit board and an electronic component manufactured using the liquid flux for flow according to [5].

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A soldering flux is obtained by mixing a raw material with a resin component, an organic acid component, an organic halogen compound, a solvent, a thixotropic agent and the like. In the present invention, the soldering flux has an acid value as a resin component in the range of 150 to 250, more preferably 150 to 24.
Rosin having a softening point in the range of 0 to 120 ° C, more preferably in the range of 120 to 140 ° C is added.
The amount of rosin added in the above range is preferably 30% by weight or more, more preferably 40% by weight or more, relative to the total rosin contained in the flux, and 20 to 60% by weight, more preferably 40% by weight, based on the total amount of flux.
５５55 wt%.

The acid value of rosin is defined as potassium hydroxide (K) required to neutralize free fatty acids contained in 1 g of rosin.
OH) in milligrams.

As the type of rosin, for example, natural rosin, disproportionated rosin, polymerized rosin, modified rosin, etc. which satisfy the above-mentioned acid value and softening point can be used.

The measurement of the softening point of rosin is carried out by a softening point measuring apparatus by the ring and ball method (ASTM No. D36 and DIN 1995). Regarding the acid value of rosin, according to DIN 55935, 0.6 g of rosin was dissolved in 50 ml of a mixed solution (1: 1) of neutral ethanol (95%) and benzene, and 0.1 N KOH was used using phenolphthalein as an indicator. Titrate and measure.

The metal composition of the solder alloy that can be used in the soldering flux of the present invention is, for example, Sn-Pb
System, Sn-Pb-Ag system, Sn-Pb-Bi system, Sn-
Pb-Bi-Ag system and Sn-Pb-Cd system are mentioned. Also, from the viewpoint of recent Pb elimination, Sn containing no Pb is used.
-In system, Sn-Bi system, In-Ag system, In-Bi
System, Sn-Zn system, Sn-Ag system, Sn-Cu system, Sn
-Sb system, Sn-Au system, Sn-Bi-Ag-Cu system,
Sn-Ge system, Sn-Bi-Cu system, Sn-Cu-Sb
-Ag system, Sn-Ag-Zn system, Sn-Cu-Ag system,
Sn-Bi-Sb system, Sn-Bi-Sb-Zn system, Sn
-Bi-Cu-Zn system, Sn-Ag-Sb system, Sn-A
g-Sb-Zn system, Sn-Ag-Cu-Zn system, Sn-
Zn-Bi system is mentioned.

In the above specific example, Sn is 63 wt.
%, Pb is 37 wt% eutectic solder (hereinafter 63Sn / 3
Expressed as 7Pb. ) And 62Sn / 36Pb /
2Ag, 62.6Sn / 37Pb / 0.4Ag, 60S
n / 40Pb, 50Sn / 50Pb, 30Sn / 70P
b, 25Sn / 75Pb, 10Sn / 88Pb / 2A
g, 46Sn / 8Bi / 46Pb, 57Sn / 3Bi /
40Pb, 42Sn / 42Pb / 14Bi / 2Ag, 4
5Sn / 40Pb / 15Bi, 50Sn / 32Pb / 1
8Cd, 48Sn / 52In, 43Sn / 57Bi, 9
7In / 3Ag, 58Sn / 42In, 95In / 5B
i, 60Sn / 40Bi, 91Sn / 9Zn, 96.5
Sn / 3.5Ag, 99.3Sn / 0.7Cu, 95S
n / 5Sb, 20Sn / 80Au, 90Sn / 10A
g, Sn90 / Bi7.5 / Ag2 / Cu0.5, 97
Sn / 3Cu, 99Sn / 1Ge, 92Sn / 7.5B
i / 0.5Cu, 97Sn / 2Cu / 0.8Sb / 0.
2Ag, 95.5Sn / 3.5Ag / 1Zn, 95.5
Sn / 4Cu / 0.5Ag, 52Sn / 45Bi / 3S
b, 51Sn / 45Bi / 3Sb / 1Zn, 85Sn /
10Bi / 5Sb, 84Sn / 10Bi / 5Sb / 1Z
n, 88.2Sn / 10Bi / 0.8Cu / 1Zn, 8
9Sn / 4Ag / 7Sb / 88Sn / 4Ag / 7Sb /
1Zn, 98Sn / 1Ag / 1Sb, 97Sn / 1Ag
/ 1Sb / 1Zn, 91.2Sn / 2Ag / 0.8Cu
/ 6Zn, 89Sn / 8Zn / 3Bi, 86Sn / 8Z
n / 6Bi, 89.1Sn / 2Ag / 0.9Cu / 8Z
n. In the case of the solder powder, a mixture of two or more kinds of solder powders having different compositions may be used.
Among them, an alloy composition containing Zn is preferably used to suitably use the soldering flux of the present invention.

When the soldering flux of the present invention is used for the thread-containing wire solder, no solvent or thixotropic agent is used for the flux, other materials are mixed at a temperature higher than the softening point of rosin, and solidified at room temperature. use. The soldering flux of the present invention can also be used as a liquid flux for flow. Even in the liquid flux for flow, the molten solder is coated with the rosin of the present invention, so that the occurrence of corners and the dewetting phenomenon of the solder alloy during melting can be suppressed. When the soldering flux of the present invention is used as a liquid flux for flow, it may be diluted to about 40 to 70% by weight using a solvent such as isopropyl alcohol.

The flux, solder paste and thread solder of the present invention are suitably used, for example, when a printed wiring board and an electronic component are joined together to produce a joint. The method of using the flux, the solder paste, the thread solder, and the like of the present invention, and the method of manufacturing an electronic component joint, for example, in the case of a solder paste, apply a solder paste to a desired portion to be soldered by a printing method or the like. The electronic component is joined to the substrate by placing the component and then heating to melt and solidify the solder particles.

The solder wire is joined to a desired portion by setting the soldering iron temperature to about 280 to 340 ° C. for a printed wiring board and about 320 to 370 ° C. for a terminal wiring.

[0015] The liquid flux for flow is applied after components are mounted on the printed wiring board in advance, and after preheating,
It is immersed in a molten solder bath to perform joining.

[0016]

The contents of the present invention will be described more specifically with reference to the following examples.

(Examples 1 and 2, Comparative Examples 1 and 2) As resin components, disproportionated rosin having an acid value of 80 and a softening point of 70 ° C. and polymerized rosin having an acid value of 150 and a softening point of 120 ° C. were used. The ratio with respect to the total rosin was as follows.

[Example 1] 40% by weight of disproportionated rosin, 60% by weight of polymerized rosin [Example 2] 100% by weight of polymerized rosin [Comparative example 1] 100% by weight of disproportionated rosin [Comparative example 2] 90% by weight of disproportionated rosin , Polymerized rosin 10
6 wt% of hydrogenated castor oil as a thixotropic agent, 0.5 wt% of n-propyl paratoluenesulfonate, 2 wt% of triethylamine, and 0.01 wt% of diphenylguanidine HBr as a ratio to the total amount of the flux. %, Hexabromostearic acid 0.34
A flux for solder paste was prepared by adding propylene glycol monophenyl ether as a solvent to 100 wt% by weight.

The flux prepared in each of the examples and the comparative examples was blended at 10 wt% and 86 Sn / 8 Zn / 6 Bi Pb-free solder powder at 90 wt% to prepare a solder paste. Each of the solder pastes of the compositions of Examples 1 and 2 and Comparative Examples 1 and 2 was printed on one circuit board, and LSI,
After placing the chip resistor and the chip capacitor on the solder paste, they were heated by a reflow heat source and soldered. A hot blast stove was used as the reflow heat source.

The reflow conditions are as follows:
The preheating time was set to 80 ° C. or 170 ° C., and the reflow was performed at a peak temperature of 220 ° C. and a reflow time of 200 ° C. or more for 50 seconds.

The solderability of the printed wiring board and the solder paste used were evaluated. The evaluation method was based on the presence of unmelted particles after solder paste reflow and the occurrence of solder balls. A specific measuring method will be described below. Table 1 shows the measurement results.

(1) Unmelted particles Until the solder after the reflow hardens, it is left horizontally, and then the pattern on the substrate and the generation state of the unmelted particles around the electronic component were examined with a magnifying glass of 40 times magnification. . A case where at least one unmelted particle was found was rejected.

(2) Solder Ball Measurement was performed in accordance with JIS Z-3284. A solder paste was printed on an alumina test plate using a metal mask, and four circular patterns having a diameter of 6.5 mm and a thickness of 0.2 mm were formed. The test plate is placed at 130 ° C. or 170
After drying at 1 ° C. for 1 minute (preheating), the solder was heated to 235 ° C. to dissolve the solder, and the board was taken out horizontally within 5 seconds after melting. The solder was left horizontally until the solder on the substrate was hardened, and then the appearance of the solder was examined with a magnifying glass of 20 magnifications, and the occurrence of solder balls around it was examined with a magnifying glass of 50 magnifications. The solder ball generation status was judged as 1 or 2 according to JIS criteria.

[0024]

[Table 1]

In Examples 1 and 2, when the flux shown in the present invention was used, generation of unmelted particles and solder balls could be largely prevented.

Further, similarly, 91Sn / 9Zn, 63Sn
A similar experiment was performed using the / 37Pb solder powder, but exactly the same results were obtained.

Further, when the structure of the solder alloy after reflow of Examples 1 and 2 was compared with the structure of the conventional Sn—Pb solder paste, the crystal structure of the Sn—Pb solder under a high temperature environment was determined. While the coarsening is remarkable, the Sn-Zn-based alloy using the flux of the present invention has a small tendency to coarsen, thereby improving the mechanical properties of the solder and improving the life characteristics of the mounting wiring board using the same. Was confirmed.

[0028]

By using the soldering flux of the present invention, generation of unmelted particles and solder balls after reflow and melting can be prevented, and extremely excellent solderability can be obtained. In particular, the present invention has remarkably improved the solderability even in the case of Pb-free solder which is considered to have poor reflowability and meltability, and its effectiveness has been confirmed.

Further, according to the present invention, it has become possible to provide a bonded product of a circuit board and an electronic component corresponding to a fine pitch of a mounting wiring board and diversification of components.

Continuation of the front page (72) Inventor Noriko Murase 1-1-1 Onodai, Midori-ku, Chiba-shi, Chiba F-term (reference) in the Research Institute, Showa Denko KK 5E319 BB05 CD21

Claims (10)

[Claims] 1. A soldering flux comprising a rosin having an acid value in the range of 150 to 250 and a softening point in the range of 120 to 200 ° C. 2. A soldering flux comprising rosin having an acid value in the range of 150 to 250 and a softening point in the range of 120 to 200 ° C. in an amount of 30% by weight or more based on the total amount of rosin in the soldering flux. . 3. A solder paste comprising the soldering flux according to claim 1 and a solder powder. 4. The solder paste according to claim 3, wherein the solder powder does not contain lead. 5. A liquid flux for flow produced from the soldering flux according to claim 1. 6. A thread-containing solder containing the soldering flux according to claim 1 and a solder alloy. 7. The thread-containing solder according to claim 6, wherein the solder alloy does not contain lead. 8. A joined product of a circuit board and an electronic component produced by using the solder paste according to claim 3 or 4. 9. A joined product of a circuit board and an electronic component produced by using the thread solder according to claim 6. 10. A bonded product of a circuit board and an electronic component produced by using the liquid flux for flow according to claim 5.