JPH07251290A - Indium based solder paste - Google Patents

Abstract

PURPOSE:To increase the shelf life of the paste by setting the acid value of rosin to form the flux vehicle to the specified value. CONSTITUTION:The solder paste is made by mixing the flux vehicle using rosin whose acid value is <=40 with the metallic powder of indium or indium alloy. Though the halogen activator is added to remove the oxide film, the halogen activator is reacted with the oxide film on the indium powder for removal, and indium becomes very active to react with the carbonic acid to form the carbonic acid indium salt. When the rosin whose acid value is reduced by esterizing the carbonic radical is used, indium is not reacted with carbonic acid, and the shelf life is increased to the same extent as that of the conventional Pb-Sn paste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a shelf life (Shelf-lif
The invention relates to indium (In) solder paste with improved e).

Since semiconductor parts are more susceptible to heat than other circuit parts, various measures have been taken to suppress deterioration due to heating even when mounted on a circuit board. That is, solder is generally used for mounting components and connecting circuits between components, and lead (Pb) and tin (Sn) are used as the materials.
The alloy of Pb-63% Sn (melting point 183 ℃) is often used, but In (melting point 156.
6 ° C.) and In alloys such as In-48% Sn (melting point 117 ° C.) are often used.

The reason why In is used here is that it has a low melting point and does not have a phase transformation, and it may be used as it is as a solder metal, but it is used for the purpose of reflow soldering or the like. For convenience, a solder paste in which a solder powder and a flux vehicle are mixed is used.

[0004]

2. Description of the Related Art A solder paste is formed by kneading a solder metal powder and a flux vehicle in a ratio of about 9: 1. Here, the flux vehicle is a rosin (Rosi).
n), thickener, antioxidant, activator and solvent.

If you use In solder paste,
It is considered to be an effective solder paste because it can perform reflow soldering at a low temperature of 0 ° C or less and can suppress the deterioration of the characteristics of semiconductor parts. However, the shelf life, which is the usable life of the paste (Shelf-life) The problem was that was extremely short.

[0006]

Many semiconductor devices have inferior heat resistance, such as deterioration in characteristics due to heating.
For example, a device including a combination of an image sensor and a photoelectric conversion element corresponds to this, and bumps made of In are used to connect both circuits.

However, as a method of mounting a plurality of semiconductor devices on a circuit board made of alumina or the like, the reflow soldering method in which a solder paste is applied to the bonding surface and passed through a tunnel furnace is most suitable for mass production.

However, the In solder paste has a remarkably short shelf life and cannot be used for such a purpose because the paste begins to harden immediately. Therefore, this improvement is an issue.

[0009]

The above problems can be solved by forming an In solder paste, which is characterized in that a rosin forming a flux vehicle having an acid value of 40 or less is used.

[0010]

[Function] The inventors have studied the cause of the shelf life of the In solder paste being extremely short, and by reacting In with a carboxylic acid in the presence of a halogen-based activator to form an indium carboxylate salt, the paste It was found that curing occurred.

In soldering, halogen is used as a constituent of the paste in order to remove the oxide film existing on the surface of the target metal and to remove the oxide film existing on the surface of the solder powder. Although a system activator such as an amine hydrohalic acid has been added, when this halogen-based activator reacts with the oxide film present on the In powder and is removed, In becomes very active and carboxylic acid is It has been found that when present, it reacts readily to form an indium carboxylic acid salt.

Since the carboxylic acid is present in the rosin, the inventors presumed that the carboxylic acid in the rosin reacts with In. FIG. 1 is a proof of this, in which the behavior of the carboxyl group contained in the rosin was investigated using proton nuclear magnetic resonance (H ⁺ -NMR), and the horizontal axis represents the resonance wavelength (ppm). The vertical axis represents the resonance intensity.

That is, the upper part shows the resonance absorption of rosin, and the arrow shows the resonance peak of the carboxyl group, which exists at the position of 10 to 13 ppm. Next, the middle row is for the flux vehicle, and the resonance peak of the carboxyl group shifts to 6 to 8 ppm, which indicates that the carboxyl group of rosin reacts with the activator. , The lower part is for the cured solder paste, and the resonance peak of the carboxyl group is 5
It has been shifted to 7 ppm, and it is considered that the carboxyl group of rosin reacted with In.

Here, when a solder paste is formed by using an organic acid as an activator in order to eliminate the reaction between the carboxyl group of rosin and the activator, since the organic acid has a carboxyl group, indium carboxylic acid salt is used. Was formed and curing was accelerated.

Therefore, the present invention uses a rosin having a reduced content of carboxyl groups, that is, a rosin having a low acid value, specifically, a rosin having an esterified carboxyl group to form a solder paste. It is a thing. Here, acid value means mg of potassium hydroxide (KOH) necessary to neutralize free fatty acids contained in 1 g of oils and fats.
Is a number.

Next, according to the experiments of the inventors, it was possible to suppress the hardening of the paste by using a rosin having an acid value of 40 or less. However, in order to obtain such rosin, the acid value was specified. Alternatively, after the rosin is purchased, it may be esterified to adjust the acid value and then used.

[0017]

EXAMPLES Example: The composition of the prototype flux vehicle is as follows. Rosin: Esterified rosin (acid value 32.9) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 60g Thickener: Hardened castor oil ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0g Antioxidant: Butylhydroxytoluene ・ ・・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0 g 〃: t-Butylhydroquinone ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0 g Activator ： 2-aminoethyl bromide hydrobromide ・ ・ ・ 0.2 wt% Br Solvent: Diethylene glycol monobutyl ether ··· 36 g After dissolving rosin in the solvent, add the above additives and knead well to make a flux vehicle, then In-48% Sn
The alloy powder (particle size: 20 to 45 μm) and the flux vehicle were kneaded at a weight ratio of 9: 1 to prepare a solder paste.

Next, in order to evaluate shelf life, the solder paste was hermetically sealed at room temperature and allowed to stand, and the state change was examined. The initial state was maintained even after 2 weeks.
It was possible to print. To check the solderability, place the solder paste on a glass substrate on which a gold (Au) vapor deposition film has been formed, and heat it to 155 ° C in an inert gas (carbon fluoride, trade name Galden) atmosphere. Then, the spread state was observed. As a result, the solder was spread uniformly, and no generation of solder balls was observed. Comparative Example: The composition of the prototype flux vehicle is as follows. Rosin: Commercially available rosin (acid value approx. 170) ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 60g Thickener: Hardened castor oil ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0g Antioxidant: Butylhydroxytoluene ・・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0 g 〃: t-butylhydroquinone ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ 1.0 g Activator ： 2-aminoethyl bromide hydrobromide ・ ・ ・ ・0.2wt% Br solvent ： Diethylene glycol monobutyl ether ・ ・ ・ ・ ・ ・ 36g After dissolving rosin in the solvent, add the above additives and knead well to make a flux vehicle, then In-48% Sn
The alloy powder (particle size: 20 to 45 μm) and the flux vehicle were kneaded at a weight ratio of 9: 1 to prepare a solder paste.

Next, in order to evaluate shelf life, the solder paste was sealed at room temperature and allowed to stand still, and the state change was examined. The paste hardened within 2 hours after preparation and printing became impossible. To check the solderability, place the solder paste on a glass substrate on which a gold (Au) vapor deposition film has been formed, and heat it to 155 ° C in an inert gas (carbon fluoride, trade name Galden) atmosphere. Then, the spread state was observed. as a result,
Remarkable solder ball generation was observed.

[0020]

By implementing the present invention, it is possible to make a paste having a long shelf life as the In solder paste as well as the conventional Pb-63% Sn paste, thereby improving the efficiency of the reflow soldering process of the semiconductor device. Can be improved.

[Brief description of drawings]

FIG. 1 is an analysis result of a solder paste by H ⁺ -NMR.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Kitajima Masayuki Kitajima 1015 Kamiodanaka, Nakahara-ku, Kanagawa Prefecture, Fujitsu Limited Fujitsu Limited (72) Inventor Shigekazu Takei 1015, Kamedotachu, Nakahara-ku, Kawasaki, Kanagawa Prefecture Fujitsu Limited

Claims (1)

[Claims] 1. A solder paste prepared by kneading a metal powder made of indium or an indium alloy and a flux vehicle, wherein the rosin forming the flux vehicle has an acid value of
Indium solder paste characterized by using 40 or less.