JPS6072696A - Soft solder flux - Google Patents

Abstract

PURPOSE:To obtain a flux by which good joinability is obtd. when used for soft brazing by consisting the flux principally or rosin or hydrogenated rosin and ammonium acetate without contg. halogen. CONSTITUTION:A soft solder flux consists principally of rosin or hydrogenated rosin and ammonium acetate and contains no halogen. Said flux provides good joinability by preventing generation of voids when used for soft soldering of the electrode parts of a semiconductor element. Such flux as well as a suitable solvent and soft solder powder are intimately mixed to a paste ink state and the mixture composed thereof is coated directly to the metallic part of a diode or the electrode part of the element and is subjected to reflow by heating in a protective or reducing atmosphere, by which direct mounting is accomplished. The above-mentioned flux is easily removed by water or an org. solvent. The similar effect is also exhibited by constituting the above-mentioned flux of zinc chloride or ammonium zinc chloride and ammonium acetate or zinc acetate, ammonium chloride, ammonium acetate, etc.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] This invention relates to a flux used for soft solder joining,
The details relate to slacks with better bonding properties.

[Prior art and its problems]

Fip b e 8 n + I n * for soft filler metal
A material containing a material with a low melting point, such as Zn#Sb, and silver is used. Conventional fluxes are roughly divided into inorganic type fluxes, which are zinc salts, and organic type fluxes, which are mainly composed of rosin.

In order to further activate both materials, a substance that generates a halogen-based element through a heating reaction during bonding is often added. At the same time, the halogen removes the oxide film of the soft soldering material and the object to be joined, and the main component is ZN as a metal salt.
Salt or bath melting in rosin is known to work by weakening the surface tension of soft wax and extending wetting.

In order to increase the effectiveness of these fluxes.

It is desirable that the metal salt produced by the thermal reaction becomes molten at the bonding temperature, dissolves in the main component, and is easily removed by an organic solvent or water after solidification. Among the soft solder components, halides such as Pb, A, and 9 have high melting points (
It is an insoluble component in water or rIi# agent. The melting point is as follows. pbc), [501°C].

PbBrz [:373℃J I A 11 Cl [
455°C), AJBr[:434].

It is easily assumed that when these components are generated during flow, they will be present on the molten surface or at the bonding interface, and will inhibit soft solder bonding since they will not dissolve in water or organic solvents even after reflow. Despite the problems associated with lead and silver-containing solders, halogen activators have been used in conventional softening bonding techniques.

[Purpose of the invention]

The present invention provides a soft solder flux suitable for areas where conventional soft solder joining techniques are problematic.

In the semiconductor field, soft solder mounts are often used, but especially when bonding the metal parts of semiconductor elements to bases and leads, commercially available flux cannot be used, and the required bonding properties cannot be obtained due to the characteristics. Therefore, the bonding is done without the use of flux.

The aim was to develop a flux suitable for this field.

[Summary of the Invention] The bondability of soft filler metals has traditionally been inspected by macroscopic means such as analysis of appearance, bond strength, and bonding surfaces, but in fields that utilize the characteristics of semiconductors, higher bondability is required. is required.

Since the desired bonding properties cannot be obtained with conventional fluxes, a method has been used in which clean soft solder preform pieces are laminated between the objects to be bonded, heated and melted in a reducing atmosphere, and bonded. A problem with this process is that voids are likely to occur in the bonding layer due to oxidation of the soft filler metal and the materials to be bonded.

- In the field of mechanical conductors, a soft solder with a medium-range melting point difference is used in consideration of the mount 1110, and in particular, a surface temperature soft solder is used for soft 9 bonding of semiconductor devices, and it is also heat-resistant that can absorb the difference in thermal expansion. Fatigue properties are also required.

pb-1%Sn to p+)-Sn eutectic Pb-a
Soft solders such as n-based, Pb-8n-Al1-based, and Pb-In-Ag are used.

The flux of the present invention uses ammonium acetate as the main activator, and has a melting point of 114°C, decomposition temperature, and 148°C. The produced Pb salt is as low as Pb (AC) [280°C], and does not cause hemorrhoids in water or organic solvents. Focusing on the fact that it is easy to use, we discovered that it is possible to obtain a flux with good bonding characteristics.

〔Effect of the invention〕

1. The flux of the present invention not only provides good bonding properties for soft solder joints in the electrode portions of semiconductor devices, but also provides good bonding properties for general soft solder joints.

2. To prevent voids that tend to occur in conventional fluxless bonding during soft soldering bonding of electrode portions, bases, and leads of semiconductor elements.

3. Mix the flux of the present invention with a suitable solvent and soft wax powder to form a best ink, apply it directly to the diode metal part or element electrode part, and directly mount it by storing or heating and phosphorizing it in a reducing atmosphere. I can do it.

4. It is a flux that can be easily removed with water or an organic solvent.

5. The flux of the present invention provides effective bonding properties especially with Pb-rich soft solder and silver-containing solder.

[Embodiments of the invention]

First, evaluation samples and methods in the semiconductor field, which are the objects of the present invention, will be explained.

Ni on both sides of 4 and 10 formed by diffusing P and Bi into silicon.
Apply soft wax best ink consisting of soft wax powder and the fluff to the diode (13) chip on which electrodes have been formed, assemble the base (11) and leads (12) as shown in Figure 1, and reflow in forming gas. After cooling directly, the specimen was subjected to ultrasonic cleaning with water or an organic solvent and used as a sample. As electrical properties of this diode, forward direction characteristics were evaluated by VF, heat dissipation characteristics ΔVF, and bonding properties were evaluated using tensile strength.

The value of VF is the voltage (V
), △VF is set as al to measure VF at 100 mA, and a surge current of 170 A and 0.1 sec is applied, and after this current is cut off, the VF value of 100 mA at 500 μs is measured again. (a)-
(b) is the value (unit: mV).

This method takes advantage of the property that the electrical resistance of a semiconductor decreases as the temperature rises, and measures the V F (b) after a certain period of time to measure the heat generated by overcurrent in the semiconductor chip, indicating the degree of heat dissipation. , ΔVF is large, indicating poor heat dissipation, which is a result of the presence of an oxide film or voids.

On the other hand, when ΔVF is small, it indicates that a bond with good heat dissipation is created, which is preferable from the viewpoint of product characteristics.

Comparative Example 1 Two commercially available solder fluxes were selected according to the above-mentioned evaluation sample preparation procedure, and a soft solder composition of P p -1w/o8n was selected and made into a best ink form using a specified diluent.

The results are shown in Table 1 after coating and reflowing at 360°C in forming gas. Soft solder set fN, Pb-5In-2, 5AJ
The temperature of the Toshiro flow was 390°C, and the results are shown in Table 2.

Comparative Example 2 P b -1w/ which was created using a lamination method using only soft solder 3φ x 0.15t without using flux and evaluated.

Sn is shown in Table 1. Similarly, Pb-5In-2,5A is shown in Table 2.

Comparative Example 3 (NH4) in 10 cc of a solvent of methyl alcohol, ethylene glycol, diquexyethanol 1:1:1
2 Melt 4.8 g of Zncl as flux,
Table 1 shows a sample prepared by adding 10% to Pb-18n powder to form a best ink according to the sample procedure described above. Similarly Pb-
The results for 5In-2,5Ag are shown in Table 2.

Example 1 Methyl alcohol, ethylene glycol, diphenoxyethanol 1:1:1, WW rosin 5 in 10cc
g or hydrogenated rosin 5g and ammonium acetate IJ 7%
It was dissolved in a heating bath, left to cool, and then used as a flux. 250fV1e
10% of the above flux was mixed with sh pb-1w10sn to form a best ink, and the same treatment as in Comparison 1 was performed, and the results obtained were similar to ww and hydrogenated rosin. The results of Soit et al. are shown in Table 1.

Similarly, 250MeshP b -5I n -2,
, 5A9 are shown in Table 2.

Example 2 Using Example 1 flux, 250Mesh 50
Table 1 shows the bonding evaluation in which w10Pb-50w10 Sn was mixed with 10% flank and the best ink was used in the same manner as in Comparative Example 1, with only the linoleum temperature being 240°C.

Comparative Example 4 was made by Comparative Example 1, Company A, Franks, as a comparative sample.

Example 3 Zinc chloride (Zncl2) 19 was added to 10 cc of the solvent of Example 1.
and ammonium acetate (NH4A c ) 1.21% as a flux %P b -1w/oS
Table 1 shows the results obtained at a temperature of 360° C. when adding 10% to N powder. Similarly, Table 2 shows the results obtained by adding 10% to Pb-5In-2,5A# powder at a temperature of 390°C.

Example 4 Ammonium zinc chloride (NH4) 2Z was used as the solvent in Example 1.
nc144.8g and ammonium acetate (NH4A e
)1g to m1! ”￥, Pb-1w10sn 10
% added.

21. Obtained at a reflow temperature of 360°C. The results are shown in Table 1. Similarly, Table 2 shows the results obtained with 10% added to Pb-5In-2,5A, 9 powder at a reflow temperature of 390°C.
Shown below.

Example 5 1 g of zinc acetate and 0 ammonium chloride were added to the solvent of Example 1.
．． 5 g and 0.55' of ammonium acetate were bathed to flux. 250'Mesb Pb-5In-2,5A
10% of this flux was added to J to form a best ink, which was mounted in the same manner as described above, and the evaluation results are shown in Table 2.

Combining the results of the Examples, (1) In the Pb-an system, it is clear from Table 1 (Comparative Examples 1a, 1b).

Comparative Example 3 shows worse bonding properties than Comparative Example 2. Example 1
．． ．． A value of 3.4 is close to that of Comparative Example 2, and good bonding characteristics can be obtained with the addition of ammonium acetate in both rosin and ZnCl2 systems. ■p b -5I Ll -2,
As for 5Ag, Table 2 shows that Comparative Example 1b and Comparative Example 3゜Example 1 have worse bonding properties than Comparative Example 2.

Chastity Examples 3, 4.5 obtained values similar to Comparative Example 2, and Z
Good bonding properties can be obtained by adding ammonium acetate only to the n-salt type. (2) Regarding Pb50%5n50%, the same value was obtained for Comparison 114 and Example 2. This result indicates that ammonium acetate has an effective effect on lead-rich compositions.

Under me Table 2 pb-5In-2,5Ag refrigeration mouth temperature 390℃

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention in detail. 11...Base, 12...Lead, 13...Diode chip, 14...Solder. Representative Patent Attorney Noriyuki Chika (and 1 other person) Figure 1

Claims (3)

[Claims] (1) Soft soft 9 which is mainly composed of rosin or hydrogenated rosin and anthonium vinegar and does not contain halogen.
Flux. (2) A soft wax flux characterized by mainly containing zinc chloride or ammonium chloride, and ammonium acetate. (3) A soft wax flux characterized by mainly containing zinc acetate, ammonium chloride, and ammonium acetate.