JPS6049636A - Mounting method of chip - Google Patents

Abstract

PURPOSE:To facilitate mounting of chips by a method wherein after an adhesive consisting of soluble and fusible solid epoxy resin, silver powder and a solvent is applied to a wafer, the wafer is divided into chips, and the individual chips are fixed by pressure to heated lead frames. CONSTITUTION:Silver paste formed by kneading a solution consisting of ethyl cellosolve acetate of glycidyl ether type epoxy resin of solid cresol novolak and silver powder is coated on the back of a silicon wafer. Then it is dried to make the resin coated surface tack freely. Then the wafer is divided into individual pieces to form chips. Then the chips thereof are fixed by pressure to heated lead frames.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for mounting a semiconductor chip on a lead frame.

Conventionally, the chip mounting method involves applying a required amount of paste-like conductive adhesive onto a lead frame using a dispenser, stamping, screen printing, etc. at a predetermined position, and then mounting the chip on top of it. The conventional method was to mount the chip by heating and curing it on a hot plate or in an oven. In contrast, conductive paste is applied to silicone wafers before dividing them into chips.
Another method has been proposed in which the chip is mounted by semi-curing it by heating appropriately, dividing it into chips, pressing the chips onto a lead frame, and heating and curing them. The latter method is clearly superior to the former method in terms of reducing man-hours and preventing chip contamination due to resin build-up. However, the drawback is that it is difficult to adjust the conditions for heating and semi-curing the paste resin. In other words, if the semi-curing is insufficient, the surface to which the resin is applied will not become tack-free, and if the semi-curing progresses too much, the surface to which the resin will be applied will not stick sufficiently even when heated, and the so-called reactivation will not be sufficient. Both are undesirable because the adhesive strength of the chip mount is significantly reduced.

As a result of various studies on these points, the present inventors decided to use a soluble and fusible thermosetting resin composition so that a tack-free resin-coated surface could be obtained immediately by simply volatilizing the solvent after coating. The present inventors have discovered that it is advantageous to use a solid resin and have accomplished the present invention. That is, the method of the present invention does not require any semi-curing process to make the resin-coated surface tack-free.

The present invention is characterized by using a conductive adhesive made of a soluble solid epoxy resin composition, silver powder, and a solvent, and the conductive adhesive is applied to silicone sea urchins before dividing. After coating, the solvent is evaporated and the adhesive is dried until it is no longer sticky, then it is divided into chips, and the resin-coated surface of each chip is pressed onto a heated lead frame and cured. This is the mounting method.

The feature of the chip mounting method of the present invention is that simply volatilizing the solvent is enough to dry the coated surface, and there is no need for semi-curing that requires adjustment of the resin reaction. No consideration is required, and a resin-coated surface that is easy to reactivate and is tack-free can be easily obtained. Moreover, it has the advantage that it is easy to adjust the thickness of the resin-coated surface, making it easy to obtain a uniform thickness, and there is no risk of the resin layer protruding and causing chip contamination. As described above, the chip mounting method of the present invention has many advantages and is extremely useful in the semiconductor component manufacturing industry.

In addition, the conductive paste for chip mounting of the present invention not only contains ionic impurities such as chlorine ions and alkali metal ions, but also contains hydrolyzable chloride groups that are hydrolyzed and released during the pressure courier test. It is essential to avoid including as much of it as possible in order to improve the reliability of semiconductor components, especially to avoid performance deterioration in humidity resistance current tests.

Therefore, the epoxy resin composition used must contain ionic impurities such as chlorine ions and alkali metal ions of 10 ppm or less, and have a hydrolyzability of 0. A/
It is preferred that the group is present at less than 500 ppm, preferably 300 ppm. For the purpose of the present invention, it is known that the high reliability thereof deteriorates in proportion to the amount of impurities contained, so it is desirable to use a highly pure epoxy resin composition.

The silver powder used in the present invention has a content of ionic impurities such as halogen ions and alkali ions of 10% each.
ppm or less, and the particle size is in the range of 0.1 to 50 μm, and if necessary, it is an appropriate mixture of slightly coarse flaky or dendritic particles and slightly fine granular particles.

Metal soap or the like may be added as a lubricant when producing silver powder, but in that case it is preferable to remove it by washing with hot water or the like. Washing is also effective in removing contamination from the surface of silver particles and in activating it, but care must be taken as it may drastically change the particle size distribution.

The mixing ratio of silver powder in the present invention is preferably 70 to 95% by weight based on composition 5-. If the amount is less than this, it becomes easy to settle and separate, and if the conductivity becomes low, it is undesirable at times, and even if it is used in excess, the conductivity does not improve much, but the cost increases significantly and the adhesive strength etc. decreases. Therefore, it is undesirable.

The epoxy resin composition used in the present invention needs to be a soluble solid and have a softening point of 60°C or higher. Even if it is liquid or solid, if the softening point is 60° C. or lower, simply evaporating the solvent is not preferable because a tack-free coated surface is not obtained. In order to meet the above requirements, the hardening agent must be solid with a slightly high softening point even if the epoxy resin is liquid, or the epoxy resin must be solid with a slightly high softening point even if the hardening agent is liquid. It is sufficient that the composition is a mixture of the two, which does not react and forms a non-tacky solid. However, for the purpose of the present invention, both the epoxy resin and the curing agent have a softening point of 6.
It is more preferable that it is solid at a temperature of 0°C or higher. Furthermore, in the EVO 6-oxy resin composition of the present invention, it is preferable to contain a curing accelerator in order to appropriately adjust the curing characteristics.
Since the amount of curing accelerator used is small, even if a liquid one is used, there is no risk of significantly lowering the softening point of the solid resin composition. It should be noted that in conventional conductive adhesives, it was desired that no solvent be used, or that the solvent be used as little as possible, and that the viscosity be as low as possible. have been used.

Further, the epoxy resin used in the present invention has a hydrolyzable halogen group content of 600 ppm or less, preferably 300 ppm or less.
It is desirable that the amount is less than ppm. For this purpose, it is preferable that the halogen content be reduced by performing purification such as alkaline washing in advance. Also, chlor ion,
10 pp of ionic impurities such as alkali metal ions
It is desirable that it be less than m. If these conditions are met and a material containing a large amount of the above-mentioned impurities is used, it is not preferable because it will cause a significant deterioration in reliability in tests such as humidity resistance current testing. Further, the epoxy resin used in the present invention preferably contains an average of 2.5 or more epoxy groups per molecule. If the polyfunctionality is lower than this, the curability deteriorates and the heat resistance of the cured product decreases significantly, which is not preferable.

Any epoxy resin that satisfies the above requirements can be used in the present invention. Typical examples are as follows. Phloroglucicyl triglycidyl ether, triglycyl ether of trihydroxybiphenyl, tetraglycyl ether of tetrahydroxybisphenol F, tetraglycyl ether of tetrahydroxybenzophenone, tetraglycyl ether of tetraphenol, epoxidized novolac, epoxidized Tri- or more polyfunctional ones such as polyvinylphenol, triglycidyl isocyanurate, triglycidyl S-1 riazine, tetraglycidyl biromellitic acid ester, triglycidyl trimellitic acid ester, diglycidyl resorcin, diglycidyl Bifunctional ones such as Diglycidyl bisphenol A1 Diglycidyl bisphenol F1 Diglycidyl bisphenol, diglycidyl ether of 51 dihydroxybenzophenone, diglycidyloxybenzoic acid, diglycidyl phthalates, diglycidyl hydantoin In order to improve heat resistance, it is desirable to appropriately mix and use these so that the functionality is 2.5 or more. In addition, special types of allylated polyphenols, such as epoxidized products of meta-allylated polyphenols made with peracid, which have a glycysyl ether group and a nuclear-substituted glycysyl group, are also similar if they meet the above conditions. It can be used for.

Among these, solid epoxidized novolacs having a softening point of 60'C or higher, particularly orthocresol novolacs, are preferred.

The curing agent used in the present invention is preferably a polyfunctional one having 2.5 or more active hydrogen groups per molecule that react with epoxy groups and participate in crosslinking. As such a compound having active hydrogen, polyvalent 9-phenols are particularly suitable. The polyhydric phenols are preferably condensates of phenols and aldehydes such as formalin, and the free phenols preferably have a weight ratio of 5 or less, preferably IM weight ratio or less. Among the phenols, those using orthocresol are particularly preferred because they have a high softening point and a low melt viscosity.

Finely divided dicyandiamide powder may still be used as a curing agent. Regardless of which curing agent is used, it is preferable to use a tertiary amine organic acid or phenol salt as the curing accelerator. The content of ionic impurities such as chloride ions and alkali metal ions in each of these curing agents and curing accelerators is preferably 10 ppm or less.

The solvent used in the present invention has a boiling point of 120°C to 150°C.
C. non-aromatic ones are preferred, such as lower alkyl monoethers, diethers, and ether acetates of glycols, such as cellosolves and carpitol. Aromatic materials 10- are not preferred because they may contaminate lead wires and the like. Further, if the boiling point is lower than this, it is undesirable because it tends to volatilize excessively during use and the viscosity and fluidity tend to fluctuate. On the other hand, if it is too high, it will not completely volatilize during the curing process and will remain, deteriorating the physical properties of the cured product, which is not preferable. Further, it is preferable that the content of ionic impurities such as chloride ions and sodium ions in the solvent used in the present invention is 10 ppm or less. Furthermore, it is preferable to select a solvent that essentially does not contain hydrolyzable halogen groups as impurities, such as epoxy resins. The amount of solvent used can be adjusted as appropriate so as to obtain the desired fluidity and facilitate the application of the desired thickness.

In the present invention, a defoaming agent may be appropriately used if necessary.

As defoamers, silicone-based, fluorine-based, and other defoaming agents can be used in almost the same way.

However, it is preferable that it is not contained in aromatic low boiling point solvents. Also, it is better not to use silicone-based materials to prevent contact failure.

The test method for ionic impurities is as follows.

For the chlorine ion, dissolve sample 15S+ in 30mQ of toluene and add 100ml of pure water! Shake for 2 hours, centrifuge the condensate layer, and use it as a test solution. Next, 15 cc of the test solution was collected with a whole pipette, and 4. mQ,
Mercury thiocyanate 0.3% by weight ethanol solution 2me
Add and dilute with pure water until the temperature reaches 25mC. The obtained test solution is used for spectrophotometry to measure the absorbance at a wavelength of 460 nm, and in comparison with a blank test, the concentration of chlorine ions contained as impurities is determined using a calibration curve prepared in advance.

Sodium ions were determined by measuring the absorbance of the above test solution at a wavelength of 330.2 nm using a flameless atomic absorption spectrometer.
In comparison with a blank test, the concentration of sodium ions contained as impurities is determined using a calibration curve prepared in advance.

The method for quantifying hydrolyzable chlorine groups in epoxy resins is as follows: Resin 1
Dissolve 0f in dioxane 3Qmu and add 0. INKO
Heat to reflux for 30 minutes with 50mc of H-x ethanol solution, then measure the amount of chlorine ions generated as 001NAgNO
3. Set the amount of hydrolyzable chlorine.

The method for measuring thermally decomposable chlorine ions using the pressure Kutzker test is as follows. Conductive paste at 200℃
, harden for 30 minutes, and then crush the cured product. 2 g of the obtained powder sample is thoroughly immersed in a decomposition crucible with 3 mC of ethanol added.

Next, after adding 40 mQ of pure water, completely seal and heat at 125℃.
Process for 20 hours. After treatment, if necessary, centrifuge and use the supernatant as the test solution.

The method for measuring ionic impurities in a test solution is the same as described above.

The method for manufacturing the conductive paste of the present invention is as follows.

First, predetermined amounts of epoxy resin, curing agent, curing accelerator, and solvent are each weighed out and kneaded to form a uniform solution or dispersion.

In this case, for kneading, a conventional stirring tank, crusher, three rolls such as an ink mill, etc. may be used alone or in an appropriate combination.

Next, a predetermined amount of silver powder is weighed out and kneaded with the resin solution to form a completely uniform paste. In this case as well, a stirring tank, extractor, three rolls, etc. are used as appropriate.

13- Defoaming the obtained pasty resin composition in a vacuum chamber. In this case, if the liquid layer of the resin composition is thick, sufficient defoaming will not be possible, so the thickness should be 100 mm, preferably 50 mm.
It is preferable to spread the mixture into a thin layer and then vacuum defoaming.

The conductive paste thus obtained needs to be stored and transported at a temperature of -15°C or lower.

Temperatures slightly higher than this are not preferred because the shelf life is significantly reduced.

The conductive paste of the present invention has the following features compared to conventional products.

(2) It has high purity, that is, it has extremely low amount of hydrolyzable chlorine groups as well as ionic impurities. As a result, the amount of ionic impurities eluted in the pressure courier test is small, and the reliability in practical use is extremely high.

(2) Excellent workability, that is, a tack-free coating surface is immediately obtained by volatilizing the bath agent after coating the silicon wafer before dividing into chips. Furthermore, this coated surface is stable even when stored at room temperature for several months, and when heated to 14-120°C to 200°C, it melts into a sticky viscous liquid and is easy to activate. Moreover, in the oven 200℃, 40 minutes; 180℃, 60 minutes; 150℃, 1
Both can be cured within 20 minutes at 350°C on a hot platen within 30 seconds.

■All other characteristics are almost the same as conventional products.

The chip mounting method using the conductive paste of the present invention is as follows.

The conductive paste of the present invention is applied to a uniform thickness on the surface of the silicone wafer that is to be bonded before being divided into chips. Coating can be performed automatically and accurately using various methods such as a roll coater, spinner, and screen printing.

Next, the solvent is evaporated from the coating film thus obtained to make it dust-free. Drying conditions vary somewhat depending on the boiling point, type, amount, etc. of the solvent used, but drying can be done quickly by applying dry air or hot air. In this case, in the resin composition of the present invention, the reaction progresses quickly even after initiation, and the properties of the resin hardly change. One of the major features is that it is easy to reactivate just by volatilization, and a resin coating film with the desired tack-free properties can be easily, stably, and immediately obtained.
It is one.

That is, it is not necessary to make the υ resin coating film tack-free by so-called semi-curing during this period.

Generally, in the case of thermosetting resins, it is common practice to semi-cure the liquid resin in state A to make it reactivable, and then heat it to a high temperature to make it insoluble and harden it to state C. It is toto. However, with conventional products, it is extremely difficult to adjust the degree of semi-curing. A major drawback was that there was a risk that the adhesiveness would be insufficient, making it difficult to obtain stable adhesion.

The present invention attempts to significantly improve this point in the process.

Room temperature is sufficient for drying the coating film of the present invention, and the drying may be accelerated by raising the temperature as appropriate.

After forming a tack-free resin coating film on the surface of the silicone wafer in this manner, the silicone wafer is divided into chips of a predetermined size. The divided chips are preheated to 120℃ to 1
By pressing the chip into a predetermined position on a lead frame heated to 80° C., the resin-coated surface of the chip is reactivated and becomes adhesive. Furthermore, it is heated to 200° C. to 350° C. to cure and bond. At this time, since the reactivation is stable and excellent, the adhesion is also extremely stable and excellent.

As described above, the chip mounting method of the present invention has great advantages over conventional methods in that the workability is particularly stable and excellent, and the reliability of the obtained semiconductor components is extremely high.

Examples will be explained below.

Example Solid cresol novolac glycysyl ether type epoxy resin 50% by ethyl cellosolve acetate
A solution of an epoxy resin composition consisting of 30 parts by weight of a chlorinated acid solution, 25 parts by weight of a 50 part by weight solution of solid cresol-based novolak in ethyl cellosolve acetate, and 0.02 parts by weight of a resorcinol salt of triethylenediamine. A silver paste is obtained by kneading 78 parts by weight of silver powder using three rolls. The epoxy resin used in this case had a softening point of 70°C, an epoxy equivalent of 205, a number average molecular weight of 580, and a hydrolyzable chloro group of 400 ppm, and the novolak used had a number average molecular weight of 4101 and a softening point of 60°C.
belongs to. Furthermore, the solvent, resin, curing agent, and curing accelerator all contain 5 chloride ions and 5 sodium ions.
ppm or less. The resulting silver paste is coated on the back side of a 3 inch diameter silicone wafer using a Niscreen printer. After drying at 80° C. for 30 minutes to evaporate the solvent, the resin-coated surface becomes tack-free. Once the resin becomes tack-free, it remains stable for several months at room temperature and can be reactivated by heating. Next, using a scriber, this silicone wafer is diced into 2 m square pieces to form chips. The coated surface of this chip was pressed for about 10 seconds on a lead frame heated to 200°C, and
- Mount the chip on a lead frame by heating and curing at 200° C. for 40 minutes. The performance of the cured silver paste is shown in Table 1, and the shelf life of the tank-free resin coated surface is shown in Figure 1.

Comparative Example: 20 parts by weight of liquid glycysyl ether type epoxy resin of bisphenol A, 1 part by weight of dicyandiamide, 00 parts by weight of resorcinol salt of trisdimethylaminomethylphenol.
A silver paste is obtained by kneading 2 parts by weight of a resin composition and 79 parts by weight of silver powder using three rolls. The epoxy resin used in this case had an epoxy equivalent of 195 and a number average molecular weight of 400.
, 800 ppm of hydrolyzable chloro groups. The obtained silver paste was coated on the back side of a 3-inch diameter silicone wafer using a screen printing machine in the same manner as in the example.
Next, the coating was heated at 80° C. for 30 minutes, but the coated surface remained sticky and no stain-free surface was obtained. If a tack-free surface is not obtained, they may stick to each other when stacked, or they may be contaminated with foreign matter, making them unsuitable for subsequent steps.

Furthermore, the heating conditions were increased to 150° C. for 15 minutes, and the resin was semi-cured and a tack-free coated surface was obtained. However, once the resin becomes tack-free, it is unstable and difficult to reactivate even after being stored at room temperature for three weeks. Next, this silicone wafer is divided into two pieces using a scriber to form chips. The coated surface of this chip is pressed onto a lead frame heated to 200°C for about 10 seconds to melt and stick the paste, and then heated at 200°C for 940 minutes to harden it, and then the chip is placed on the lead frame. mount it.

The performance of the cured silver paste is shown in Table 1, and the shelf life of the semi-cured resin coated surface is shown in Figure 1.

Table 1: Performance of cured silver paste Pressure tester test The amount of chlorine ions eluted during treatment at 125°C for 48 hours was extremely large, which indicates that IC
This means that the aluminum electrodes on the chip are likely to corrode, which significantly reduces practical reliability. Furthermore, once the resin coated surface has become tack-free, it has poor stability at room temperature, and related to this, the mounting strength rapidly decreases with the storage period, so the period of storage at room temperature is short.

21-

[Brief explanation of drawings]

FIG. 1 shows the change in chip mounting strength/350°C with respect to the storage period at 25°C of the resin layer coated on the chip and dried to make it tack-free. The solid line is an example, and the broken line is a comparative example. Patent applicant Sumitomo Bakelite Co., Ltd. 22-

Claims (3)

[Claims] (1) (A) Soluble and fusible solid epoxy resin composition 5-
30 parts by weight, [F]) 70 to 95 parts by weight of silver powder, and (C
) After applying a conductive adhesive using a solvent to silicone wafers before dividing, the solvent is volatilized and dried until the tackiness disappears, then the conductive adhesive is divided into chips, and the resulting individual chips are separated. A semiconductor chip mounting method characterized by pressing a resin-coated surface onto a heated lead frame and curing it. (2) All solid epoxy resin compositions have a softening point of 60°C.
Claim (1) consists of the solid epoxidized novolak, solid novolak, and curing accelerator as described above.
Mounting method described in section. (3) The mounting method according to claim (1) or (2), wherein the solid epoxy resin composition has a hydrolyzable chlorine group of 500 ppm or less.