JPH0567670B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a conductive resin paste used for die bonding semiconductor elements to lead frames or ceramic substrates. This invention relates to a conductive resin paste that allows for electrical contact (electrical contact according to Ohm's law). More specifically, the present invention relates to a conductive resin paste that has a high thixotropy and is highly workable with very little sag or stringiness during application with a dispenser. [Prior Art] Conventionally, methods for die bonding semiconductor elements to lead frames, etc. include the gold-silicon eutectic method, in which gold and silicon are bonded by forming a eutectic, and the solder bonding method, in which they are bonded using solder paste. Legal has been mainly used. The gold-silicon eutectic method has drawbacks such as extremely high costs due to the use of gold, and high working temperatures of 400 to 450 degrees Celsius, which can lead to deterioration of semiconductor devices and parts. On the other hand, although the solder bonding method is relatively low cost, it has drawbacks such as poor heat resistance and deterioration of semiconductor elements due to solder ball scattering. Under these circumstances, a resin bonding method using a conductive resin paste in which silver powder is dispersed in an epoxy resin has recently come into widespread use. This resin bonding method has the advantage of being able to significantly reduce costs and curing at a low temperature of 200°C or less. However, since it is in the form of a semi-paste, when the paste is applied with a dispenser, unnecessary dripping occurs and thread breakage is difficult, which tends to cause problems such as the paste adhering to the stitching portion of the lead frame. In addition, since silver powder is dispersed in epoxy resin, which is originally an insulator, gold
It was inferior in terms of conductivity compared to the silicon eutectic method. Furthermore, in the initial process of curing the resin paste, the reaction does not progress much and only the temperature rises, so the viscosity of the paste decreases significantly and silver powder tends to settle. Therefore, there were also disadvantages such as the silver powder being diluted directly under the semiconductor element, resulting in a decrease in conductivity. For the reasons mentioned above, conductive resin pastes cannot be used in devices that particularly require ohmic contact. [Purpose of the Invention] The present invention has been made as a result of intensive studies aimed at solving the above-mentioned drawbacks of the prior art and obtaining a conductive resin paste with excellent conductivity and workability. Contrary to expectations, adding a small amount of ultrafine silica particles of 0.005 μm to 0.02 μm improves conductivity, prevents sagging and stringiness, significantly improves workability, and further improves flaky silver powder. It was discovered that adding a small amount of finer spherical silver powder increases the probability of silver powder bonding and also improves conductivity, thereby achieving the present invention. [Structure of the Invention] The present invention provides: (A) 70 to 95% by weight of flaky silver powder with a particle size of 1 to 50 μm and 30 to 5% of spherical silver powder with a particle size of 0.1 to 0.5 μm;
(B) Ultrafine silica powder with an average particle size of 0.005 to 0.02 μm, (C) A phenol novolac compound and a latent amine compound, (D) Hydrolyzable chlorine that is liquid at room temperature. The content is
Epoxy resin with a content of 500 ppm or less, (A), (B), (C) and (D) as essential components, 65 to 80% by weight of silver powder mixture (A), and ultrafine silica powder (B).
The present invention relates to a conductive resin paste for semiconductors characterized by containing 0.3 to 3% by weight. The silver powder used in the present invention is a mixture of flaky silver powder with a particle size of 1 to 50 μm and spherical silver powder with a particle size of 0.1 to 0.5 μm, and is a silver powder containing 5 to 30% by weight of spherical silver powder. . Particle size of flaky silver powder is 1μm
If it is less than 50 μm, the conductivity will be significantly reduced, and if it is more than 50 μm, the workability will be extremely poor, which is not preferable. In addition, spherical silver powder is added to help the flakes contact each other by dispersing them between them and to stabilize the conductivity, but the particle size
If it is less than 0.1 μm, the conductivity will not be stabilized, and if it is more than 0.5 μm, the conductivity will decrease, which is not preferable. If the blending ratio of spherical silver powder is less than 5%, the conductivity will not be stabilized,
If it exceeds 30%, the conductivity decreases, which is not preferable. Further, in the present invention, 0.3 to 3% by weight of ultrafine silica having a particle size of 0.005 to 0.02 μm is added, but although this ultrafine silica is originally an insulator, when added, the conductivity improves. This is because when curing a conductive paste, in the initial stage of curing, the reaction does not progress much and only the temperature rises, causing the viscosity to drop rapidly and the silver powder particles to settle. However, when a small amount of ultrafine silica is added, this happens. It is thought that conductivity is improved because silver powder is prevented from settling. Additionally, when a small amount of ultrafine silica is added, the thixotropy of the paste increases significantly, causing the paste to drip unnecessarily from the tip of the syringe needle when applied with a dispenser, or cause the paste to become stringy due to poor thread breakage. Furthermore, problems such as the tip sticking to the stitched portion of the lead frame are completely eliminated, and workability is extremely improved. Further, the present invention is characterized in that a phenol novolak and a latent amine compound are used together as a curing agent. Non-latent amine compounds tend to react even at room temperature and have extremely poor storage stability, making them unusable.If a latent amine compound is used, the curing temperature is high; it does not react below 150℃, but the reaction proceeds rapidly when the temperature exceeds 150℃, so it must be stored. Although it has excellent properties, the viscosity decreases rapidly during the initial curing process, and the silver powder particles tend to settle, resulting in a large amount of resin immediately below the back surface of the pellet, reducing conductivity. On the other hand, phenol novolak has a high melt viscosity and cures even at relatively low temperatures, so when it is used as a curing agent, the viscosity decreases little even during the initial curing process.
It is possible to obtain a cured product with excellent conductivity and less precipitation of silver powder. However, since phenol novolac is solid and has a large equivalent of hydroxyl groups that react with epoxy groups, it is necessary to blend a large amount of it, and when used alone, the viscosity of the paste increases significantly, making it unsuitable for practical use. By using a latent amine compound having a smaller equivalent than that of phenol novolak, it is possible to obtain a paste whose viscosity is not so high that it can be used practically. In this way, the present invention uses a combination of phenol novolac and a latent amine compound as a hardening agent, adds a small amount of the ultrafine particle silica mentioned above, and uses flaky silver powder and finer spherical silver powder as silver powder. Due to the synergistic effect of using silver powder in combination, the silver powder does not settle at all during the initial curing process, and it is also excellent in establishing bonds between silver powders, allowing for ohmic contact that has not been seen with conventional conductive resin pastes. This makes it possible to obtain a paste with very good conductivity. The phenol novolak used in the present invention is a novolak resin mainly composed of trinuclear to heptanuclear bodies obtained by reacting phenol with formaldehyde. Examples of latent amine compounds include carboxylic acid hydrazides such as adipic acid hydrazide, dodecanoic acid dihydrazide, isophthalic acid hydrazide, and p-oxybenzoic acid dihydrazide, and dicyandiamide. The epoxy resin used in the present invention is limited to one that is liquid at room temperature, but if it is not liquid at room temperature, a solvent will be required for kneading with silver powder. Solvents cause bubble generation and significantly reduce the conductivity of the cured product, making them unusable. Additionally, the amount of hydrolyzable chlorine contained in the epoxy resin is limited to 500 ppm or less, but by using such an epoxy resin, the amount of chlorine extracted from the conductive paste can be significantly reduced. I can do it. Extracted chlorine causes corrosion of aluminum wiring on the surface of semiconductor elements, so the smaller the amount extracted, the higher the reliability. The hydrolyzable chlorine content is measured as follows. That is, 0.5g of epoxy resin is mixed with dioxane.
Completely dissolve in 30 ml, add 5 ml of 1N KOH solution (ethanol solution), and boil and reflux for 30 minutes. Add 100ml of 80% acetone water to this, and
Add 2 ml of Conc.HNO ₃ and perform potentiometric titration with a 0.01N-AgNO ₃ aqueous solution. Epoxy resins used in the present invention include, for example, bisphenol A, bisphenol F, diglycidyl ether obtained by the reaction of phenol novolak and epichlorohydrin, which is liquid at room temperature, vinyl cyclohexene dioxide, dicyclopentadiene dioxide, aryl Cycloaliphatic epoxies such as cyclic diepoxy-adipate, and even n
-Butyl glycidyl ether, glycidyl persate acid ester, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether, and dicyclopentadiene diepoxide are commonly used as diluents for epoxy resins. Furthermore, among the above epoxy resins, those having a boiling point of 250°C or higher are very useful. This is because the resin pastes used have low volatility of the resin, so the viscosity does not change much even when used continuously. The reason why the silver powder content in the conductive resin paste is set to 65 to 80% by weight in the present invention is that if it is less than 65% by weight, the conductivity of the cured product will be significantly reduced. On the other hand, if it exceeds 80% by weight, the viscosity of the paste becomes too high and it becomes practically unusable. Similarly, the amount of ultrafine silica powder was set at 0.3 to 3% by weight, because if it is less than 0.3% by weight, it is too small and the desired effect of the present invention cannot be obtained sufficiently, and if it is more than 3% by weight, it is inherently insulating. This is because, since it is a substance, adding it causes problems such as a decrease in conductivity and an excessively high thixotropy of the paste, making it difficult to dispense the paste and making it difficult to work with. Furthermore, in the present invention, a curing accelerator,
A coupling agent, an antifoaming agent, etc. can also be added. [Effects of the Invention] As described above, the conductive resin paste for semiconductors according to the present invention has extremely excellent conductivity of the cured product and enables ohmic contact. It can also be applied to semiconductor devices, ie, memory devices, transistors, diodes, etc. In addition, assembly productivity is improved because no paste dripping or stringiness occurs during application with a dispenser. Furthermore, since the amount of hydrolyzable chlorine contained is extremely small, corrosion of the aluminum wiring on the surface of the semiconductor element is unlikely to occur, and reliability can be improved. [Example] Examples 1 to 4 A flaky silver powder (hereinafter referred to as silver powder a) with a particle size of 1 to 50 μm and an average particle size of 3 μm, and a spherical silver powder (hereinafter referred to as silver powder a) with a particle size of 0.1 to 0.5 μm and an average particle size of 0.2 μm Diglydyl ether (hydrolyzable chlorine content 300 ppm, epoxy equivalent 180, liquid at room temperature, The epoxy resin A), the phenol novolac and the latent amine compound were blended in the proportions shown in Table 1 and kneaded using a triple roll to obtain a conductive resin paste. After degassing this conductive resin paste in a vacuum chamber at 2 mmHg for 30 minutes, various performances were evaluated by the following methods. Stringability A pin with a diameter of 1 mmφ was sunk into the conductive resin paste to a depth of 5 mm, and the pin was pulled up at a speed of 300 mm/min to measure the height when the paste broke. Paste dripping 5 ml of paste was put into a syringe fitted with a needle with an inner diameter of 0.6 mm, placed vertically on a test tube stand with the needle facing down, and after 30 minutes, the weight of the paste dripping at the tip of the needle was measured. Volume resistivity Paste on a glass slide with a width of 4 mm and a thickness of 4 mm.
After coating to a thickness of 30 μm and curing in an oven at 200° C. for 1 hour, the volume resistivity of the cured product was measured. Ohmic contact property A diode was assembled using the paste as a die bonding material, and the ohmic contact property was evaluated. Amount of chlorine Finely grind the hardened paste and add it to distilled water.
The sample was treated at 125°C for 20 hours, and the amount of chlorine extracted was measured. The evaluation results are shown in Table 1. Comparative Examples 1 to 3 Conductive resin pastes were obtained in exactly the same manner as in the examples using the blending ratios shown in Table 1. The evaluation results are shown in Table 1. Comparative Example 4 Same as Example 1 except that diglycidyl ether obtained by the reaction of bisphenol A and epichlorohydrin (hydrolyzable chlorine content 950 ppm, epoxy equivalent weight 180, liquid at room temperature, hereinafter referred to as epoxy resin B) was used as the epoxy resin. A conductive resin paste was obtained in exactly the same manner. The evaluation results are shown in Table 1. 【table】

Claims (1)

[Scope of Claims] 1 (A) Flake-like silver powder with a particle size of 1 to 50 μm 70 to
95% by weight and 30% spherical silver powder with particle size 0.1~0.5μm
A silver powder mixture consisting of ~5% by weight, (B) ultrafine silica powder with an average particle size of 0.005 to 0.02 μm, (C) a phenol novolac compound and a latent amine compound, (D) liquid at room temperature and hydrolyzable. chlorine content is
Epoxy resin with a content of 500 ppm or less, (A), (B), (C) and (D) as essential components, 65 to 80% by weight of silver powder mixture (A), and ultrafine silica powder (B).
A conductive resin paste for semiconductors characterized by containing 0.3 to 3% by weight.