JPS63160367A - Plastic-sealed semiconductor device - Google Patents

Abstract

PURPOSE:To enhance the thermal resistance against a solder material and the reliability against dampproofness by a method wherein an iron-related lead frame is used as a lead frame whose part to be sealed by using a thermosetting epoxy resin molding material is formed by a film containing copper, zinc or the like in the form of a metal and/or its compound. CONSTITUTION:An epoxy resin molding material is normally the epoxy resin molding material for semiconductor-sealing use, e.g., a cresol-novolac epoxy resin, a phenol- novolac epoxy resin or a material which is composed by adding a hardening agent to a brominated substance of each of these epoxy resins. An iron lead frame is composed of an iron/nickel alloy; the part to be sealed is formed by a film composed mainly of at least one out of metals, i.e., copper, zinc, tin, nickel, and/or its compound whose adhesion performance in relation to a sealing resin is good; the surface roughness of the coated film is made to be at least more than 1 mum according to the requirement in order to strengthen the adhesion between this coated film and a sealing resin; in addition, it surface is treated by various chemical processes so that the affinity to the sealing resin can be enhanced. Accordingly, the airtightness is excellent; no crack is caused at the package when the package is treated by heating a solder material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a resin-sealed semiconductor device, and particularly to a resin-sealed semiconductor device that has excellent solder heat resistance.

[Conventional technology]

Metals, ceramics,
There are two types: hermetically sealed products using glass or the like, and resin-sealed products that are mainly made of epoxy resin molding materials. Although the former has excellent airtightness and heat resistance, it has poor productivity and is extremely expensive. On the other hand, although the latter is slightly inferior in airtightness and heat resistance to the former, it is extremely advantageous economically because it can be mass-produced. Moreover, recently, the reliability of various types of resin-sealed semiconductors has been greatly improved, so that more than 80% of all semiconductor products are now resin-sealed. However, in recent years, as the capacitance of semiconductor elements increases, the chip size has significantly increased.

Furthermore, it is desired that the package shape be made smaller and thinner in order to increase the packaging density, and as the chip size increases, the thickness of the sealing resin layer tends to decrease. Therefore, the requirements for thermal shock resistance of the sealing resin have become even more severe. In particular, recently the package shape has changed to DILP (Dual In-Line Pac) to allow high-density mounting of components.
kage ) and Z I P (ZigzagInnin
8Package) to FP
P (Flat Plastic Package)
, S OP (Small Outline Pack
age), 80 J (Small 0utline
Jbendel package), P L CC (
Plastic Leaded Chip Carrier
r) Surface mounting has changed to molded packages, and when conventional DILP and ZIP components are soldered to the board, only the tips of the leads are heated with solder, and the package itself is not directly exposed to high temperatures. , PPP, 80P
, 80J or PLCC, etc., infrared reflow or paper reflow soldering methods have been adopted for soldering of type packages, and the entire package has come to be directly exposed to high temperatures. Therefore, when a package contains more than a certain amount of moisture, the moisture evaporates inside the package, and the vapor pressure causes cracks in the package, which has become a major problem in the package's soldering heat resistance [Part 23] Annual proceedings repairability fixes (25th annual
proceeding5re1.1ability
physics), pp. 192-197 (1985))
.

In addition, when comparing the moisture resistance reliability of sealed products before and after soldering heat treatment, the reliability level decreases due to thermal shock during solder heating, and it is desired to improve the solder heat resistance from the viewpoint other than package cracking. .

In order to solve this problem, the above literature proposes a method of making a hole in a part of the package to make it easier for the vaporized water vapor to scatter inside the package, but this method is not suitable for resin-sealed semiconductor devices. If the air-tightness, which is a drawback of the device, is further deteriorated, there is a risk that the moisture resistance reliability of the device will be deteriorated. However, since this problem is thought to be largely caused by the adhesiveness between the sealing resin and the lead frame, Japanese Patent Application Laid-Open No. 1231.62/1987 discloses a method for making a lead frame with a through hole in the lead part of the lead frame. A method has been proposed in which a large number of recesses are provided on the back surface of a semiconductor element mounting portion (bed portion) of a frame, and an intricate uneven shape is provided at the periphery of the bed portion.

This method has the effect of significantly improving the crack resistance of the package compared to the case where no special processing is applied to the lead frame, but it also addresses the aforementioned trends of larger chips and smaller and thinner packages. [Problems to be solved by the invention] Imposition is a problem in which mold packages have poor solder heat resistance, especially package cracks, which occur when the package absorbs moisture. In order to solve this problem, it is sufficient to prevent the cage from absorbing moisture. However, as long as plastic materials are used as sealing materials, it is extremely difficult to eliminate moisture absorption to varying degrees with current technology. Additionally, package cracks occur because the high-temperature strength of the sealing resin is less resistant to the stress generated by the water vapor pressure generated inside the package, so if the high-temperature strength (heat resistance) of the sealing resin is significantly improved, Although this problem can be solved, for example, polyimide resin, which has excellent heat resistance, has poor adhesion to lead frames, and also has a significantly higher moisture absorption rate than epoxy resin. Another possibility is to use a polyfunctional epoxy or a polyfunctional curing agent as the epoxy resin to increase the density and improve heat resistance by cross-linking the cured resin, but such highly cross-linked resins still have high hygroscopicity as a cured product. This cannot be a sufficient solution to poor solder heat resistance.

The present invention was developed in view of the above-mentioned circumstances, and its purpose is to develop resin-sealed semiconductor devices that are less susceptible to deterioration in solder heat resistance, especially package cracks, even when left in high humidity environments. It is about providing.

[Means for solving problems]

To summarize the present invention, the present invention relates to a resin-sealed semiconductor device, in which a metal lead frame and a semiconductor element mounted on the lead frame are sealed with a thermosetting epoxy resin molding material. In the sealed semiconductor device, the lead frame has a coating containing at least 1 m of a metal and/or compound selected from the group consisting of copper, zinc, tin, and nickel formed on at least the resin-sealed portion thereof. It is characterized by its iron-based lead frame.

As a result of a detailed study of the mechanism of occurrence of poor solder heat resistance, especially package cracks, the present inventors found that in resin-sealed semiconductor devices, the recon board, lead frame, and sealing resin that make up the semiconductor device, etc. Because the thermal expansion coefficients of the semiconductors are significantly different, if the semiconductor is sealed at a high temperature (generally 160 to 190°C) and then the sealed product is cooled to room temperature, or the sealed product is cooled to room temperature after secondary curing, each configuration will be different. Thermal stress occurs in the encapsulating resin due to the difference in the amount of thermal contraction of the materials, and this thermal stress causes peeling at the adhesive interface between the lead frame and the encapsulating resin. Moisture can enter the inside of the package through the grooves, reducing moisture resistance reliability.If the sealed product is heated in this state, the package will deform (bulge) due to the vapor pressure of the moisture vaporized inside the package, causing package cracks. It has been shown that it can be induced. Therefore,
In order to improve the soldering heat resistance of the package, it is necessary to minimize the difference in the coefficient of thermal expansion of each material that makes up the semiconductor device to reduce the occurrence of thermal stress, and at the same time further improve the adhesion between the lead frame and the encapsulating resin. The present invention has been made because it is clear what should be done.

In order to achieve the above objective, as mentioned above, it is necessary to increase the adhesive strength between the lead frame and the encapsulating resin, and in addition, the bonded area can be damaged by the thermal stress generated by the various heat treatments that the encapsulated product undergoes in the post-processing process after encapsulation. In order to prevent peeling, it is important to make the thermal expansion coefficients of the materials constituting the semiconductor element as similar as possible.

Of all the materials that make up resin-encapsulated semiconductor devices, encapsulation resin has traditionally had the largest coefficient of thermal expansion, but recently, spherical inorganic fillers have become more highly packed, and paste resins have a higher coefficient of thermal expansion than epoxy resins. By using a polyimide resin with a very small coefficient of expansion, it has become extremely easy to lower the coefficient of thermal expansion of the sealing resin to about 1-OXlo-s/°C. On the other hand, the lead frame also has a small thermal expansion coefficient of 4270 mm (17 x 1 a-''/c), and the combination of these materials significantly reduces the thermal stress generated in the sealed product.

However, since iron-based frames generally have poor thermal conductivity, copper-based frames with a large coefficient of thermal expansion are often used from the viewpoint of heat dissipation. This copper-based frame generally has good adhesion to the sealing resin, but has a large coefficient of thermal expansion. Therefore,
The present inventors have proposed that copper, zinc, tin, etc., which have good adhesion to the sealing resin, be used in at least the resin-sealed portion of the iron-based lead frame.
A film containing at least 11a of nickel metal and/or compound as a main component is formed, and the surface roughness of the film is roughened as necessary to further strengthen the adhesion between the film and the sealing resin. Furthermore, it has been found that the adhesive force with the sealing resin can be significantly improved by subjecting the surface to various chemical conversion treatments to increase the affinity with the sealing resin.

The lead frame and the encapsulating resin containing a large amount of inorganic filler have extremely good mutual adhesion and have a coefficient of thermal expansion very close to that of silicon wafers, so semiconductor devices made of these materials cannot be heated through solder heat treatment. Even if such a thermal shock is applied, the thermal stress generated due to the difference in the coefficient of thermal expansion of each material is extremely small.

In other words, the resin-sealed semiconductor device of the present invention has extremely excellent airtightness, and even when left under high temperature and high humidity, there is little moisture intrusion into the package, and the adhesive between the encapsulation resin and the lead frame can be easily maintained. Due to its good quality, package cracks do not occur during solder heat treatment. Furthermore, because the amount of deformation during heating is small, the thermal stress exerted on the joint between the gold wire and the lead aluminum electrode pad, the aluminum wiring, etc. is also small, and the moisture resistance is reliable even when thermal shocks such as those in soldering heat treatment are applied. The epoxy resin molding material in the present invention refers to an epoxy resin molding material usually used for semiconductors and encapsulation, such as cresol novolac type epoxy resin, phenol novolac type epoxy resin, Phenol novolak resin, acid anhydride, amines, etc. are added as a curing agent to bisphenol A type epoxy resin or brominated products of these epoxy resins, and if necessary, a curing accelerator, filler, flame retardant aid is added. , a coupling agent, a mold release agent, a coloring agent, and other various additives. Among the above-mentioned additives, the filler is an extremely important material in relation to the coefficient of thermal expansion and thermal conductivity of the molded article, and powders of silica, alumina, etc. are generally used. In particular, a filler made by melting ore into a spherical shape by thermal spraying into a fine powder can be blended in larger amounts without impairing the fluidity of the molding material, compared to a angular filler made from finely pulverized ore. This is extremely important in achieving low thermal expansion and high thermal conductivity of molded products.

Next, the iron-based lead frame of the present invention refers to an iron/nickel-based alloy (for example, 4270), and at least one of copper, zinc, tin, or nickel metal and/or compound coated on the resin-sealed part. A film containing seeds as a component is formed by an electric or electroless plating method, and the surface roughness of the film can be adjusted by changing plating conditions such as current density and deposition temperature. Further, after plating, the surface can be roughened by chemically etching with a cupric chloride/hydrochloric acid aqueous solution, an ammonium persulfate aqueous solution, or the like. Furthermore, chemical treatments to increase the affinity of the coating for the sealing resin include application of a coupling agent, chromate treatment, heated aqueous solution of 3-sodium phosphate/sodium hydroxide/sodium chlorite, and ammonium acetate/sodium chlorite.
A chemical conversion treatment using a heated aqueous solution of copper acetate/copper sulfate/ammonium chloride/ammonia aqueous system or the like can be used.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The invention is not limited to these examples.

Examples 1 to 6 Copper, brass, and tin/nickel alloy were applied to the resin-sealed part of the lead frame made of 42 alloy (Ni: 42% by weight, balance: 9Fe) with a thickness of 10 to 15 μm and a surface roughness of 2 to 5 μm.
Electroplated to fall within the range of . The copper-plated lead frame is further treated with an aluminum chelate coupling agent, chromate treatment, and oxidized with a heated aqueous solution of ammonium acetate/copper acetate/copper sulfate/ammonium chloride/ammonia, resulting in a total Afil type lead frame. prepared.

After mounting a semiconductor element having aluminum zigzag wiring on the above lead frame and bonding a gold wire, the molding material was sealed with an epoxy resin molding material. Partially brominated bisphenol type A 10
l Epoxy modified silicone resin 15
1 Phenol novolac resin 54
I Antimony trioxide 81 Montanic acid ester 21 Carbon black 21 were kneaded for about 10 minutes with a twin-screw roll heated to about 80°C, cooled, and then ground and tableted. A transfer molding machine was used for molding, the mold temperature was 180°C, and the molding pressure cuff 5 was gf/
crn", and the curing time was 1.5 minutes. The molded product was then subjected to secondary curing at 180°C for 6 hours and then subjected to the test. The molded product made of the above molding material had a linear thermal expansion coefficient of 1.OX.
The temperature was 10″S/°C.

Comparative Examples 1 and 2 A semiconductor element was mounted on a 4270I lead frame without plating, and a gold wire was bonded in the same manner as in the above example, and then the linear thermal expansion coefficient was reduced by reducing the amount of the epoxy molding material and filling row. It was sealed with a molding material made larger.

Comparative Examples 3 to 6 The copper-plated lead frame used in the above examples was further treated with an aluminum chelate coupling agent, chromate treatment, and oxidation treatment. A semiconductor element was mounted on a lead frame and a gold wire was bonded to the lead frame, which was thermally expanded. It was sealed with a molding material with a large coefficient.

Next, each resin-sealed semiconductor device obtained above was heated to 65°C.
The temperature at which cracks occur in the package was measured when each device was heated with an infrared lamp after being left under 95% RH for 168 hours to absorb moisture.

Separately, we also investigated the standing time when each resin-sealed semiconductor device obtained above was immersed for 30 seconds in a smoldering bath heated to 260°C, and then left at 121°C and 100 sRH, and the aluminum wiring. We investigated the relationship with the corrosion breakage failure rate.

The results of the above study are shown in Table 1.

From Table 1, it can be seen that the resin-sealed semiconductor device of the present invention has excellent solder heat resistance (cracking resistance) after moisture absorption and moisture resistance reliability after solder heat treatment. As shown, the resin-sealed semiconductor device of the present invention has excellent adhesion between the lead frame and the encapsulating resin, and the thermal expansion coefficients of each component material are close to each other, so it is difficult to apply thermal shock such as solder heating. In this case, the thermal stress generated due to the difference in thermal expansion coefficients is small, so that peeling of the adhesive interface and damage to the gold wire joints will not occur.Soldering heat resistance and moisture resistance reliability are extremely good.

Claims (1)

[Claims] 1. In a resin-sealed semiconductor device in which a metal lead frame and a semiconductor element mounted on the lead frame are sealed with a thermosetting epoxy resin molding material, the lead frame has at least A resin characterized in that it is an iron-based lead frame in which a coating containing at least one member selected from the group consisting of copper, zinc, tin, and nickel in the form of a metal and/or a compound is formed on the resin-sealed part. Sealed semiconductor device. 2. The resin-sealed semiconductor device according to claim 1, wherein the coating has a surface roughness of at least 1 μm or more. 3. The resin-sealed semiconductor device according to claim 1, wherein the surface of the coating is chemically treated to impart affinity with the resin. 4. The resin-sealed mold according to claim 1, wherein the sealing resin and the lead frame on which the coating is formed have thermal expansion coefficients of 1.4 x 10^-^3/°C or less. Semiconductor equipment.