JPH0351782B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is directed to materials for electronic devices having excellent mechanical strength, corrosion resistance, low coefficient of thermal expansion, plating adhesion, etc., especially iron containing chromium or nickel, which is suitable as ceramic for semiconductors or resin-sealed lead frame material. It concerns base alloys. Conventionally, high nickel alloys such as Kovar alloy (Fe-29Ni-16Co) and 42 alloy (Fe-42Ni) and alloys such as phosphor bronze are well known as lead frame materials. The lead frame supports the semiconductor IC circuit chip and is required to stably hold it within the device, so it is extremely important that the lead frame has good mechanical strength. Although the above-mentioned known alloys possess these properties, the former high nickel alloy is hard and has poor ductility, and has the disadvantage that it is difficult to roll it to an accurate thickness when manufacturing lead frame materials. In addition, the latter phosphor bronze has a large thermal expansion, and if it is made into a sealed capsule made of ceramic or the like, there is a risk that the seal between the lead frame and the capsule will break due to thermal stress during manufacturing or use. . Moreover, all of these alloys are extremely expensive, limiting their use in light of the current drive to manufacture semiconductor IC circuits at low cost. For this reason, the present inventor has decided to use an iron-based alloy containing chromium or nickel as the lead frame material, which is inexpensive, has good mechanical properties, good workability, and has a low coefficient of thermal expansion. I devised a. However, lead frame materials are generally plated with gold or silver to provide electrical connection, but the adhesion of the silver plating layer applied to the iron-based alloy containing chromium or nickel is poor, resulting in poor adhesion to semiconductor integrated circuit devices. It has been found that during the assembly process, the plating layer blisters and peels off due to heating during wire bonding, sealing, etc. The cause of this blistering is not necessarily clear, but the area around the chromium carbide formed on the surface of the iron-based alloy lead frame material is susceptible to electrochemical corrosion, resulting in the formation of minute corrosion grooves. It is thought that dirt from the processing of the lead frame remains in the groove, and when the plated lead frame material is added afterwards, the residue in the groove expands and causes blistering of the plated layer. Further, oxygen in iron-based alloys tends to precipitate in large amounts at grain boundaries, and such carbon reduces plating adhesion. In any case, it is not preferable to use the chromium-containing iron-based alloy as a lead frame material as it is, even considering the material's strength, low thermal expansion, and low cost. As a result of intensive research on this point, the inventor of the present invention has found that by controlling the carbon content of the iron-based alloy containing chromium or nickel to 0.05% by weight or less, preferably 0.03% by weight or less, the blistering of the plating layer can be prevented. We were able to significantly reduce the phenomenon. That is, the present invention contains carbon of 0.05% by weight or less, more preferably 0.03% by weight or less, and chromium of more than 10.5% by weight and less than 20% by weight, or 1% by weight thereof.
It has been found that an iron-based alloy for lead frames containing 15% by weight or less of nickel has excellent plating properties. As a result, the iron-based alloy for lead frames of the present invention has the characteristics of having good mechanical strength, corrosion resistance, good workability, low thermal expansion, excellent plating adhesion, and low cost. be. In the iron-based alloy used for the lead frame material of the present invention, the chromium content must be more than 10.5% by weight and less than 20% by weight. This is because if chromium is less than 10.5% by weight, sufficient strength and corrosion resistance cannot be obtained, and if it exceeds 20% by weight, heat-resistant strength cannot be obtained and corrosion resistance is poor. Furthermore, the amount of nickel added is 1
% by weight or more and 15% by weight or less. Nickel is not used alone, but in combination with chromium, for the purpose of improving heat resistance and corrosion resistance. The carbon content is 0.05% by weight or less, preferably 0.03% by weight or less. If the carbon content exceeds 0.05% by weight, blistering of plating occurs frequently and adhesion of plating deteriorates. At 0.03% by weight or less, almost no blisters occur. In addition, magnesium, silicon,
The total amount of additional elements or impurities such as molybdenum, phosphorus, sulfur, aluminum, copper, etc. is 1% by weight or less. Next, an example will be described. Example Sample piece of each component composition shown in Table 1 (25mm x
50 mm x 0.25 mm (thickness)) was processed as follows and subjected to evaluation. Each sample piece was first subjected to acetone ultrasonic degreasing treatment, followed by alkaline degreasing treatment, then alkaline electrolytic degreasing treatment and pickling treatment, followed by silver meshing of 2.5 μm. To evaluate the plating quality, we heated the silver plated surface at 450°C for 5 minutes under conditions similar to the heating conditions used during wire bonding in integrated circuit assembly work, and measured the number of blisters that occurred per 1 cm ² of the silver plated surface. . Sample numbers 3-5, 8-10 and 13 in Table 1
All of Samples 1 to 17 have a carbon content exceeding the range of the present invention, and as the carbon content increases, the number of blisters in the plating layer increases rapidly. On the contrary, sample numbers 1 to 2, 6 to 7, and 11 to 12, which fall within the scope of the alloy of the present invention, had zero or very few blisters and were sufficiently usable as lead flake materials. From the above, it can be seen that the alloy of the present invention is rich in mechanical strength, heat resistance, corrosion resistance, etc., and has excellent plating properties without blistering as described above.

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Claims (1)

[Claims] 1 More than 10.5% by weight of chromium and not more than 20% by weight, carbon
Iron-based alloy for lead frames consisting of 0.05% by weight or less, the balance being iron and unavoidable impurities. 2. The iron-based alloy for lead frames according to claim 1, which contains 0.03% by weight or less of carbon. 3 More than 10.5% by weight and less than 20% by weight of chromium, 1% by weight and less than 15% by weight of nickel, 0.05% by weight of carbon
The following is an iron-based alloy for lead frames consisting of the balance iron and unavoidable impurities. 4. The iron-based alloy for lead frames according to claim 3, which contains 0.03% by weight or less of carbon.