JPH04370184A - Electrically conductive paste - Google Patents

Abstract

PURPOSE:To obtain a paste, containing a benzophenone group-containing urethane prepolymer, a polyhydric alcoholic compound, a bisphenol and electrically conductive powder, excellent in moisture and hydrolytic resistance and adhesion and responsive to large-sized semiconductor chips. CONSTITUTION:The objective paste containing (A) a urethane prepolymer, preferably composed of a blocked isocyanate prepolymer prepared by blocking terminal active isocyanate groups with an active hydrogen compound and having benzophenone groups in the molecule, (B) a polyhydric alcoholic compound such as a compound having a long-chain alkyl group or a polyester-based, a polybutadiene-based or silicone-based compound, (C) a bisphenol such as bisphenol A or bisphenol F and (D) electrically conductive powder such as silver, copper or Ni as essential components.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used for assembling semiconductor devices and adhering various parts, and particularly to a conductive paste suitable for increasing the size of semiconductor chips and surface mounting.

0002

[Prior art] ICs and L
The process of connecting semiconductor chips such as SI is one of the important processes that affects the long-term reliability of the device. Conventionally, this connection method involves bonding the silicon surface of the semiconductor chip to the gold-plated surface of the lead frame under pressure.
The Si eutectic method was the mainstream. However, in recent years precious metals,
In particular, with the soaring price of gold as an opportunity, resin-sealed semiconductor devices are becoming more expensive.
There is a rapid transition from the u-Si eutectic method to methods using solder, methods using conductive paste, etc.

However, although some methods using solder have been put into practical use, it has been pointed out that the solder and solder balls scatter and adhere to electrodes and the like, causing corrosion and disconnection. On the other hand, in the method using a conductive paste, an epoxy resin mixed with silver powder is usually used, but in terms of reliability, it is not as satisfactory as the Au-Si eutectic method. When using a conductive paste, it has advantages such as superior heat resistance compared to the soldering method, but since the resin and curing agent are not made for bonding semiconductor devices, it may cause voids or It was inferior in moisture resistance and hydrolysis resistance, promoted corrosion of the aluminum electrode, and often caused disconnection defects, and the reliability of the device was inferior to that of the Au-Si eutectic method. Furthermore, as semiconductor chips such as ICs, LSIs, and LEDs become larger and various types of frames, such as those made of copper, are introduced, chip cracks and a decrease in adhesive strength occur, which has become a problem.

0004

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances. The present invention aims to provide a highly reliable conductive paste that is free from warpage and compatible with larger semiconductor chips.

[0005]

[Means for Solving the Problems] As a result of intensive research aimed at achieving the above object, the present inventor discovered that a paste having the composition described below can achieve the above object,
This completes the present invention.

That is, the present invention is characterized in that (A) a urethane prepolymer having benzophenone groups in the molecule, (B) a polyhydric alcohol compound, (C) bisphenol, and (D) conductive powder as essential components. It is a conductive paste with

The present invention will be explained in detail below.

As the urethane prepolymer (A) having a benzophenone group in the molecule used in the present invention, all urethane-forming prepolymers and oligomers can be used, but desirably a terminal active isocyanate group is used. This is a blocked isocyanate prepolymer blocked with an active hydrogen compound. To introduce a benzophenone group, a polyester or polybutadiene having a terminal active isocyanate is blocked with a blocking agent such as acetoacetate oxime or phenol, and benzophenone tetracarboxylic dianhydride, etc. is heated to react with the polyester or polybutadiene. can do. These can be used alone or in combination of two or more. These blocked urethane polymers and oligomers are stable at room temperature, but at 120°C
It has the property of dissociating isocyanate groups when heated to a higher temperature.

The polyhydric alcohol compound (B) used in the present invention includes those having a long chain alkyl group in consideration of flexibility and pliability, as well as polyester-based, polybutadiene-based and silicone-based polyhydric alcohol compounds. is available. Specifically, R- manufactured by Idemitsu Petrochemical Co., Ltd.
45HT, polyethylene glycol and polypropylene glycol manufactured by Sanyo Chemical Co., Ltd., alcohol-modified silicone BY series manufactured by Toray Silicone Co., Ltd., etc., and these can be used alone or in combination of two or more. The hydroxyl groups of these polyhydric alcohol compounds react with the isocyanate groups dissociated from the urethane polymers and oligomers having benzophenone groups in their molecules. The blending ratio of this urethane polymer or oligomer and polyhydric alcohol is determined by the ratio of dissociated isocyanate groups (NCO) to hydroxyl groups (OH) of the polyhydric alcohol compound (NCO/OH).
is preferably in the range of 1.0 to 1.2 equivalents. If this blending ratio is less than 1.0 equivalent or more than 1.2 equivalent, the desired characteristics cannot be obtained, which is not preferable. Further, as a catalyst for promoting this reaction system, dialkyltin dilaurate or the like is generally used.

Examples of the bisphenol (C) used in the present invention include bisphenol A and bisphenol F, and these can be used alone or in combination of two or more.

[0011] Examples of the conductive powder (D) used in the present invention include silver powder, copper powder, nickel powder, and silver powder having a metal layer on the surface, and these may be used alone or in a mixture of two or more. be able to. These conductive powders are
In both cases, it is desirable that the average particle diameter is 10 μm or less. If the average particle size exceeds 10 μm, the composition will not become paste-like and the coating performance will deteriorate, which is not preferable. The mixing ratio of the conductive powder and the resin component is 70/30 to 70/30 by weight.
A ratio of 90/10 is desirable. The conductive powder is 70
If it is less than 90 parts by weight, satisfactory conductivity cannot be obtained;
If it exceeds 1 part by weight, workability and adhesion will deteriorate, which is undesirable.

The conductive paste of the present invention comprises (A) a urethane prepolymer having benzophenone groups in the molecule;
B) polyhydric alcohol compound, (C) bisphenol, and (D) conductive powder are essential components, but antifoaming agents, coupling agents, and others may be added as necessary and within the scope of the purpose of the present invention. Additives can be added.

The method for producing a conductive paste of the present invention involves reacting a urethane prepolymer having a benzophenone group in its molecule with a polyhydric alcohol compound, adding bisphenol and conductive powder, and then, for example, using a three-roll process. It can be produced by kneading and then defoaming under reduced pressure. The conductive paste produced in this way is filled into a syringe, discharged onto a lead frame using a dispenser, and after bonding semiconductor elements, wire bonding is performed, and the conductive paste is sealed with a resin sealing material to form a resin-sealed semiconductor. The device can be manufactured. This semiconductor device is heated to 280℃
It was confirmed that even when heated at a temperature of It was done.

[0014]

EXAMPLES Next, the present invention will be explained by examples, but the present invention is not limited by these examples. In the examples, "parts" means "parts by weight" unless otherwise specified.

[Example of synthesis of urethane prepolymers having benzophenone groups in the molecule] Urethane prepolymers A and B were produced by heating and reacting each composition shown in Table 1.

[0016]

[Table 1] *: Trade name of a 50% butyl carbitol solution of polybutadiene-based phenol-blocked urethane prepolymer manufactured by Idemitsu Petrochemical Co., Ltd.

Examples 1 to 4 The components shown in Table 2 were mixed and further mixed with three rolls.
Each conductive paste was manufactured by kneading three times.

Comparative Example A commercially available epoxy resin-based solvent-based conductive paste was obtained.

Using the conductive pastes of Examples 1 to 4 and Comparative Example, a semiconductor chip and a lead frame were connected and fixed under the semiconductor chip bonding conditions shown in Table 3 to manufacture semiconductor devices. For these semiconductor devices, adhesive strength,
Semiconductor chip warpage and hydrolyzable chlorine tests were conducted. The conductive paste was also tested for moisture absorption properties. The results are shown in Table 3, and the effects of the present invention could be confirmed.

[0020] The adhesive strength was measured by adhering a 4 x 12 mm silicon chip onto a 200 μm thick lead frame (copper-based) and using a push-pull gauge at a temperature of 350°C. The warpage of the chip was measured by measuring the surface of the chip after curing using a surface roughness meter, and was expressed as the distance between the center of the chip and the edge. Hydrolyzable chlorine is extracted from CI by curing the conductive paste under semiconductor chip adhesion conditions, pulverizing it to 100 mesh, and heating and extracting it at 180°C for 2 hours.
The amount of ions was measured by ion chromatography. In the moisture absorption property test, the amount of moisture absorbed in water vapor at a temperature of 121° C. and a pressure of 2 atmospheres was measured.

[0021]

[Table 2] *: Manufactured by Idemitsu Petrochemical Co., Ltd., product name: Acid group compound

[0022]

[Table 3] (Unit)

[0023]

Effects of the Invention As is clear from the above explanation and Table 3, the conductive paste of the present invention has moisture resistance, hydrolysis resistance,
It is a highly reliable conductive paste that has excellent adhesive properties and is free from voids and breakage and warping due to corrosion of aluminum electrodes, making it compatible with larger semiconductor chips.

Claims (1)

[Claims] Claim 1: A conductive material comprising (A) a urethane prepolymer having a benzophenone group in the molecule, (B) a polyhydric alcohol compound, (C) bisphenol, and (D) conductive powder as essential components. paste.