JPH0521343B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a resin-sealed semiconductor device, and particularly to a resin-sealed semiconductor device with excellent solder heat resistance. [Prior Art] There are two types of packaging for semiconductor devices: hermetic sealing products using metals, ceramics, glass, etc., and resin sealing products mainly using 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 has slightly lower airtightness and heat resistance than 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 devices 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 shape of the package has become DILP due to the high density mounting of components.
(Dual In-Line Package) and ZIP (Zigzag
From pin insertion type such as Inline Package) to FPP
(Flat Plastic Package), SOP (Small Outline)
Package), SOJ (Small Outline Jbended)
package), PLCC (Plastic Leaded Chip)
Carrier) has changed to an imposition type package cage,
When conventional DILP and ZIP components are soldered to a board, only the tip of the lead is heated with solder, and the package itself is not directly exposed to high temperatures, but surface-mounted packages such as FPP, SOP, SOJ, or PLCC Infrared reflow and paper reflow methods have been adopted for soldering, and the entire package has come to be directly exposed to high temperatures.
Therefore, if the package contains more than a certain amount of moisture, the moisture will evaporate inside the package.
The soldering heat resistance of the package has become a major problem as the vapor pressure causes cracks in the package [23rd Annual Proceedings, Reliability Physics (23rd Annual Proceedings, Reliability Physics)
annual proceedings reliability physics) No. 192
~197 pages (1985)]. In addition, when comparing the moisture resistance reliability of sealed products before and after soldering heat treatment, it was found that the reliability level decreased due to thermal shock during solder heating, and it is desirable to improve solder heat resistance from a perspective other than package cracks. It is rare. 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. This will further reduce the airtightness, which is considered a drawback, and in particular, there is a risk that the moisture resistance reliability of the device will deteriorate. In addition, since this problem is thought to be caused by the adhesiveness between the sealing resin and the lead frame, Japanese Patent Application Laid-Open No. 123162/1983 proposes that a hole be made in the lead part of the lead frame, and that a semiconductor element be mounted on the lead frame. A method has been proposed in which a large number of recesses are provided on the back surface of the bed portion or a complicated uneven shape is provided on 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. Therefore, more drastic measures were needed. [Problems to be solved by the invention] Poor solder heat resistance of surface-mounted packages, especially package cracks, is a problem that occurs when the package absorbs moisture.In order to solve this problem, it is necessary to prevent the package from absorbing moisture. good. 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. In addition, package cracks occur because the high-temperature strength of the sealing resin is lower than the stress generated by the water vapor pressure generated inside the package, and the high-temperature strength (heat resistance) of the sealing resin has been significantly improved. However, 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 cross-linking density of the cured resin and improve its heat resistance, 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 has been made in view of the above-mentioned circumstances, and its purpose is to provide a resin-sealed semiconductor device that is less susceptible to deterioration in solder heat resistance, especially package cracking, even when left in high humidity. Our goal is to provide the following. [Means for Solving the Problems] To summarize the present invention, the present invention relates to a surface-mounted resin-sealed semiconductor device, and includes a metal lead frame and a semiconductor element mounted on the lead frame. In a surface-mount resin-sealed semiconductor device sealed with a curable epoxy resin molding material, the lead frame has at least one resin selected from the group consisting of copper, zinc, tin, and nickel in at least the resin-sealed portion thereof. A lead frame made of an iron-nickel based alloy in which a coating made of a metal and its compound, or a coating made of a compound of the metal is formed with a surface roughness of 1 μm or more, and the sealing resin and the coating are formed. The thermal expansion coefficient of each of the lead frames is in the range from the thermal expansion coefficient of the semiconductor silicon element chip to 1.4×10 ^-5 /°C or less. As a result of a detailed study of the mechanism by which poor solder heat resistance occurs, particularly package cracks, the inventors found that:
In resin-encapsulated semiconductor devices, the silicon substrate, lead frame, encapsulation resin, etc. that make up the semiconductor device have significantly different coefficients of thermal expansion, so the semiconductor is encapsulated at a high temperature (generally 160 to 190°C). When the post-sealed product is cooled to room temperature or the sealed product is cooled to room temperature after secondary curing, thermal stress is generated in the sealing resin due to the difference in the amount of thermal contraction of each constituent material, and this thermal stress causes the lead frame to Peeling occurs at the adhesive interface between the sealing resin and the sealing resin, and if such a sealed product is left in high humidity, moisture will infiltrate into the package through the peeled part, lowering the moisture resistance reliability, and the sealing in such a state When a frozen product is heated, the package deforms (bulges) due to the vapor pressure of the moisture vaporized inside the package.
It has been shown that this can induce package cracks. 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 to improve the adhesion between the lead frame and the encapsulating resin. It became clear that further improvements could be made, leading to the present invention. 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 also to reduce the thermal stress generated by the various heat treatments that the encapsulated product undergoes in the post-processing process after encapsulation. Therefore, in order to prevent peeling from occurring at the bonded portion, it is important to make the coefficients of thermal expansion of the materials constituting the semiconductor element as similar as possible. Of all the materials that make up resin-sealed semiconductor devices, the sealing resin has traditionally had the largest coefficient of thermal expansion, but recently, spherical inorganic fillers have become highly filling, and base resins with higher thermal expansion coefficients than epoxy resins have been used. By using a polyimide resin with a fairly small coefficient of expansion, the coefficient of thermal expansion of the sealing resin is 1.0×10 ^-5 /
It has become extremely easy to lower the temperature to about ℃. On the other hand, the thermal expansion coefficient of 42 alloy for the lead frame is small (0.7×10 ^-5 /°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 used at least one metal selected from the group consisting of copper, zinc, tin, and nickel and a compound thereof, which has good adhesion with the sealing resin, at least in the resin-sealed portion of the iron-based lead frame. In order to strengthen the adhesion between the coating and the sealing resin, the surface roughness of the coating is roughened as necessary, and various coatings are added to the surface. It has been discovered that the adhesive strength with the sealing resin can be significantly improved by applying a chemical conversion treatment to increase the affinity with the sealing resin. That is, in the present invention, the lead frame is an iron-based lead frame on which the coating is formed with a surface roughness of 1 μm or more, and the coefficient of thermal expansion of the sealing resin and the lead frame on which the coating is formed are such that The desired effect could be achieved by setting the thermal expansion coefficient to be extremely close to that of the semiconductor chip, in the range from the thermal expansion coefficient of the semiconductor chip to 1.4×10 ^-5 /°C or less. 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 can be processed using soldering heat treatment. Even if 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 there is good adhesion between the sealing resin and the lead frame. Therefore, 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 joints of gold wires and leads or aluminum electrode pads, aluminum wiring, etc. is also small, and even when thermal shocks such as those in soldering heat treatment are applied, moisture resistance and reliability are maintained. There is little deterioration or variation in device characteristics. The epoxy resin molding material in the present invention refers to an epoxy resin molding material that is normally used for semiconductor encapsulation, such as cresol novolac type epoxy resin, phenol novolak type epoxy resin, bisphenol A type epoxy resin, or any of these. Phenol novolac resin, acid anhydride, amines, etc. are added as a curing agent to the brominated epoxy resin, and if necessary, a curing accelerator, filler, flame retardant aid, coupling agent, mold release agent, etc. are added. , and various additives such as colorants. Among the above additives, fillers are extremely important materials in relation to the thermal expansion coefficient and thermal conductivity of molded products.
Generally, powders of silica, alumina, etc. are used. In particular, fillers made by finely pulverizing raw stones and then melting them into spheroidal shapes by thermal spraying can be blended in large amounts without impairing the fluidity of the molding material, compared to angular fillers made from finely pulverized raw stones. , is extremely important in achieving low thermal expansion and high thermal conductivity of molded products. Next, referring to the iron-based lead frame and iron/nickel-based alloy (for example, 42 alloy) of the present invention, a coating containing at least one metal of copper, zinc, tin, or nickel is coated on the resin-sealed part. is formed by electric or electroless plating method,
The surface roughness of the coating of 1 μm or more can be adjusted by changing the 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 coupling agent application, chromate treatment, and 3-sodium phosphate/sodium phosphate treatment.
A chemical conversion treatment using a heated aqueous solution of sodium hydroxide/sodium chlorite, a heated aqueous solution of ammonium acetate/copper acetate/copper sulfate/ammonium chloride/ammonia, etc. can be used. [Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Examples 1 to 6 Copper, brass, tin/nickel alloy is applied to the resin-sealed part of a lead frame made of 42 alloy (Ni: 42% by weight, remaining Fe) with a thickness of 10-15 μm and a surface roughness of 2-2.
Electroplating was performed to fall within the range of 5 μm. 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 of 6 types of lead frames. prepared. A semiconductor element having aluminum zigzag wiring was mounted on the lead frame, bonded with gold wire, and then sealed with an epoxy resin molding material. The following molding materials are used: o-Guzol novolac type epoxy resin 90 parts by weight Brominated bisphenol type A
10 Epoxy-modified silicone resin 15 Phenol novolac resin 54 Tetrabutylphosphonium tetraphenylborate 1.5 Antimony trioxide 8 Fused silica (spherical, average particle size 6 μm) 830 parts by weight r-glycidoxypropylmethoxysilane
2 montanic acid ester 2 carbon black 2 were kneaded for about 10 minutes with a twin-screw roll heated to about 80°C, cooled, and then ground into tablets. A transfer molding machine was used for molding, mold temperature 180℃, molding pressure 75Kgf/cm ² , curing time 1.5
I was there in minutes. The molded product was then subjected to secondary curing at 180°C for 6 hours and then subjected to testing. Note that the linear thermal expansion coefficient of the molded article of the above molding material was 1.0×10 ⁻⁵ /°C. Comparative Examples 1 and 2 A semiconductor element was mounted on a 42 alloy lead frame without plating, and gold wire was bonded in the same manner as in the above example, and then linear thermal expansion was achieved by reducing the amount of the epoxy molding material and filler blended. It was sealed with a molding material with a large coefficient. 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, and a semiconductor element was mounted on the lead frame and gold wire was bonded to the lead frame. was sealed with a large molding material. Next, each resin-sealed semiconductor device obtained above was left at 65°C and 95% RH for 168 hours to absorb moisture, and then the temperature at which cracks occur in the package when each device was heated with an infrared lamp was determined. It was measured. Separately, we also investigated the standing time and aluminum wiring when each resin-sealed semiconductor device obtained above was immersed for 30 seconds in a solder bath heated to 260°C and then left at 121°C and 100% RH. We investigated the relationship between corrosion and disconnection failure rate. The results of the above study are shown in Table 1.

【table】

〔Effect of the invention〕

As mentioned above, 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 constituent material are close to each other. Even when soldering is applied, the thermal stress generated due to the difference in thermal expansion coefficient is small, so peeling of the adhesive interface and damage to the gold wire joint are unlikely to occur, and the soldering heat resistance and moisture resistance reliability are extremely good. .

Claims (1)

[Claims] 1. A surface-mount 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 which the lead frame is At least on the resin-sealed portion, a coating made of at least one metal selected from the group consisting of copper, zinc, tin, and nickel and a compound thereof, or a coating made of a compound of the metal is formed with a surface roughness of 1 μm or more. The lead frame is made of an iron-nickel based alloy, and the coefficient of thermal expansion of the sealing resin and the lead frame on which the film is formed are both 1.4× higher than the coefficient of thermal expansion of the semiconductor silicon chip.
A surface-mounted resin-sealed semiconductor device characterized by a temperature range of 10 ^-5 /℃ or less. 2. The surface-mounted resin-sealed semiconductor device according to claim 1, wherein the coating has a surface roughness of 1 to 5 μm. 3. The surface-mounted resin-sealed semiconductor device according to claim 1, wherein the surface of the coating is chemically treated to impart affinity with the resin.