JPH0375346A - Production of high strength and high conductivity type metallic sheet for lead frame - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a metal for lead frames that has an excellent balance of strength and heat dissipation (heat dissipation is almost equivalent to conductivity, therefore, hereinafter abbreviated as conductivity). Metal plates for lead frames for low-cost ICs and LSIs, other high-strength transistors, capacitors, etc. that enable wire bonding of gold and copper wires without plate or gold or silver plating (hereinafter referred to as bare bond). -Relating to a method of manufacturing a metal plate for a highly conductive lead frame.

[Conventional technology]

Metals for high-strength, high-conductivity type lead frames such as IC and LSI are Cu-0.15% by weight Cr-0.35% by weight Zr; Cu-0.60% by weight Fe-0.20% by weight P. -0.05% by weight Mg system; Cu-0.12% by weight5
n-O, SO wt% Cr system; Cu-0,12 wt% 5n
-0.80 wt% Cr system; Cu-0.55 wt% Cr-
0.25% by weight Zr-based; Cu-0.02% by weight 5n-0
, 80% by weight Cr system; Cu-^1□03 internal oxidation alloy etc. have high strength and high conductivity, especially Cu-Cr-
Zr-based materials have also been developed for bare bonding, but there are problems such as increased costs due to the addition of alloying elements and increased manufacturing processes, and restrictions on adding alloying elements that are difficult to melt and refine. Today's surface-mount QFs have a large anisotropy due to the high secondary processing rate.
There are problems in that it cannot be used in P (frames with leads on all sides) packages, and no copper-plated metal has been developed that satisfies both price and characteristics.

[Problem to be solved by the invention]

The present invention solves the problems of these prior art techniques by combining a rapid solidification casting method and trace additive elements to create a Cu-plated metal that achieves an excellent balance between strength and high conductivity, as well as reliability with excellent bare bonding properties and low cost. A method of manufacturing a metal plate for lead frames is provided.

[Means to solve the problem]

That is, the feature of the present invention is that O is 0% by weight.
．． 005 to 0.05%, Zr 0.1 to 0.3%, and further contains at least one of Ti or Cr,
Surface cooling rate of 100° C./second or more until the molten metal completely solidifies, with the total of Zr, Ti, and Cr being regulated to a range of 0.5 to 1.0% and the remainder being Cu and inevitable impurities. A metal plate for a high-strength, high-conductivity type lead frame can be obtained by casting, then performing the steps of cold rolling and heat treatment one or more times, and further applying Cu plating after the final cold rolling or heat treatment. It's in the manufacturing method.

[For production]

The reasons for limiting the constituent elements of the present invention will be explained below.

The reason for limiting the chemical composition of the alloy is as follows.

In the present invention, first, micro oxides of Zr, which are most likely to form oxides, are subjected to matching strain to the matrix during rapid solidification and cooling (if oxides, precipitates, etc. are present in the matrix, the continuous crystal lattice is slightly shifted). The solid solution Zr that remains after bonding with oxygen in the subsequent treatment equivalent to aging is strengthened by making it exist in a state with an interfacial strain that occurs at the interface when the Zr is in a state of
Ti and Cr are finely precipitated to give consistent strain, and the total volume of oxides and precipitates used for strengthening is minimized to obtain strength, making it possible to simultaneously achieve high strength and high conductivity.

The reason why the total zero content is limited to 0.005 to 0.05% by weight is that if it is less than 0.005% by weight, the effect of Zr oxide on primary strengthening is insufficient, so the lower limit is set to 0.005% by weight. If the content exceeds 0.05% by weight, the Zr oxide becomes coarse and deteriorates workability and bare bonding properties, so the upper limit was set at 0.05% by weight.

Next, adjust the amount of Zr, Ti, and Cr from 0.5 to 1.
The reason why the content is in the range of 0% by weight is as follows.

Figure 1 shows the relationship between the total content of Zr, Ti, and Cr and the strength (kg/mm2) and total elongation (%) of the metal plate.
As shown in the figure, strength and total elongation exhibit completely opposite properties, and the optimum range for both properties is 0.5 to 1.0% by weight of the total amount of the above components.
is within the range of

In addition, Figure 2 shows the total amount of the above components and the electrical conductivity (%) of the metal plate.
IACS) and bare bond ratings, and the optimum range for both properties is within the range of 0.5 to 1.0% by weight of the total amount of the above components.

That is, if the total amount of the above components is less than 0.5% by weight, the total volume of oxides and precipitates formed on the metal plate will be insufficient and the necessary strength will not be obtained, and if it exceeds 1.0% by weight. This is because if the amount is too much, workability, bare bonding properties, and electrical conductivity will be significantly deteriorated. Furthermore, the above Zr is a main constituent element of the present invention, and if its content is 0.1% by weight or less, it is insufficient for reinforcement by Zr oxide and reinforcement by a compound of Cu and Zr. If it exceeds 0.1%, the cost will increase due to the price of Zr.
It was limited to a range of 3% by weight.

The rest are raw materials and impurities that are inevitably mixed in during melting.

The surface cooling rate until the molten metal completely solidifies is 100%.
The reason for setting the cooling rate to ℃/sec or higher is that if the oxide cooling rate is less than 100℃/sec, it will not be possible to obtain the fine size and consistent strain needed to obtain the desired strength, and the uniform distribution of the oxide will not be achieved. This is because it becomes difficult to obtain.

In the present invention, casting is performed by a rapid solidification method such as a twin roll method, and in addition to the above-mentioned effects, this method also improves the strength after aging by making the structure finer and improving the supersaturated solid solubility of Zr, Ti, and Cr. It is possible to obtain the effect of
There are also significant cost benefits such as improved yield.

In addition, after casting, cold rolling and heat treatment are performed.The main purpose of cold rolling is to obtain the necessary plate thickness for the lead frame.
- The rolling rate of the next cold rolling is selected based on the combination of chemical composition, casting thickness, and secondary cold rolling reduction rate so that the desired plate thickness, strength, and workability can be obtained. The effective rolling reduction range is 30-95%.

The purpose of heat treatment for annealing is to improve workability, but if necessary, it can also serve as heat treatment for aging by controlling cooling to near room temperature after annealing test. Further, the heat treatment temperature at this time is classified into recovery type annealing and recrystallization type annealing, and a temperature range of 300 to 700°C is appropriate as a temperature range that includes both. Furthermore, aging treatment may be performed to further improve thermal and electrical conductivity, and the appropriate treatment temperature should be selected depending on the chemical composition and pre-process conditions. That is, if the above-mentioned temperature is too low, a large strain is generated around the precipitate, deteriorating the conductivity, and the heating time becomes longer, which limits the equipment and manufacturing efficiency. On the other hand, if the temperature is too high, the amount of precipitates decreases and good conductivity cannot be obtained, and the precipitates become coarse, which is disadvantageous in terms of ensuring strength.

Therefore, the temperature range of 350 to 650°C is the appropriate condition for aging treatment. Further, performing secondary cold rolling as necessary is effective for ensuring the shape, surface roughness, and strength of the plate, and is added in accordance with the required characteristics of the package.

In addition, when performing bare bonding, by applying Cu plating after the final cold rolling or heat treatment, the Cu plating surface is maintained as it was immediately after plating, and by providing a pure Cu surface, the reliability of wire bonding is further improved. be.

〔Example〕

Example 1 Table 1 shows the chemical compositions of alloys A to E in the composition range of the present invention and comparative materials F-J in the comparative composition range.

Table 1 (wt%) (1*Epli$ Table 2, which shows components outside the invention range, shows the material properties of the obtained alloys. Here, sample numbers 1 to 10 are .8X A plate thickness of 2.On+ ring was cast with a surface cooling rate of 102°C/sec, and sample number 11 was cast with a thin slab continuous casting machine to a plate thickness of 10.5mm at a cooling rate of 10°C/sec, which is outside the present invention. It is.

After pickling, the plate was rolled to a thickness of 1.0 mm as the next cold rolling.
Intermediate annealing was performed at 00℃ for 1 hour, and the plate thickness was further reduced to 0.25℃.
＋＾Rolled until clear skies. Next, final annealing was performed at 550°C for 3 hours to impart workability, and from this temperature to 100°C, 5
After cooling at a cooling rate of 0° C./hour, secondary cold rolling was performed by 30%.

As for property evaluation, tensile strength and total elongation are JIS No. 13 B.
The electrical conductivity of the test piece was evaluated using the four-terminal method.

In addition, the price index is 60% or less of the price of typical high-strength, high-conductivity materials.
The values above are shown as x marks.

Here, sample number 6 is O content, sample number 8 is Zr, Ti
, the total amount of Cr is below the component limit, and the strength is low. Also, sample number 7 has 0 content, sample number 9 has Zr,
Sample No. 10, in which the total amount of Ti and Cr is above the component limited range and has low overall density and conductivity, has Zr above the component limited range and is expensive. Further, as mentioned above, sample No. 11 has a surface cooling rate outside the range of the present invention and has low strength, so it is clear that the properties of the present invention are excellent.

Table 2 Example 2゜Table 3 shows A of Table 1 processed and heat treated in Example 1,
Bare bond properties were evaluated using samples C, E, G and ■. The conditions were to slit the above coil to a width of 25.64 mm, punch it for DIP-16Pin, apply Cu plating to 3 μm depending on the sample, apply 5 μm Ag plating, and die bond the S1 chip to 25 μm.
Wire bonding was performed using atmospheric ultrasonic thermocompression bonding using gold wire. Bonding conditions are atmosphere 10μm2
The N2 lead frame temperature was 195°C, the first bonding pressure was 50B, and the second bonding pressure was 90g.

Bonding strength was evaluated by measuring the bonding strength with a pull tester, and then molding the bonded lead frame with epoxy resin and holding it in a pressure cooker at 130°C for 200 hours with 12V applied to check for disconnections and short circuits. It was measured. From this result, even when the material of the present invention was not plated, the bondability of the lead frame was comparable to that when Ag plating was applied.

Table 3 Example 3 In Table 4, bare bond properties were evaluated using samples A, C, E, G, and ■ in Table 1, which were processed and heat treated in Example 1 in the same manner as Example 2. . The conditions are that the above coil is 25.
Slit to 64mm+width and punched for DIP-16P in. Depending on the sample, Cu and plating may be 3μ.
+a, Ag plating was applied to 5 μm and the Si chip was die-bonded, and then wire bonding was performed using a 25 μm (F) copper wire by an atmospheric ultrasonic thermocompression method. The bonding conditions were an atmosphere of 10% H2N2, a lead frame temperature of 195° C., a first bonding pressure of 50 g, and a second bonding pressure of 90 g. The bondability evaluation conditions were also the same as in Example gA2. The results show that even in copper wire, the component system within the scope of the present invention has bare bonding properties similar to those of ordinary Ag-plated materials, oxygen-free steel, etc.

Table 4 [Effects of the Invention] The present invention replaces the method of strengthening metal plates for lead frames conventionally used in ICs, LSIs, transistors, and capacitors by As we aim to improve strength by minimizing this, we are able to obtain a better balance of strength and conductivity than conventional materials, and since the matrix is close to pure Cu, it has excellent bonding reliability during bare bonding. Thus, the present invention can provide a high-strength, high-conductivity metal plate for lead frames at low cost.

[Brief explanation of drawings]

Figure 1 shows the relationship between the total content of Zr, Ti, and Cr, strength, and workability (total elongation), and Figure 2 shows the relationship between the total content of Zr, Ti, and Cr.
, is a diagram showing the relationship between the total content of Cr, bare bonding property, and conductivity.

Claims (1)

[Claims] 1.0.005 to 0.05% by weight of O and 0.05% by weight of Zr.
1 to 0.3%, further contains at least one of Ti or Cr, and the total of Zr, Ti, and Cr is 0.5 to 0.3%.
The molten metal, the balance of which is regulated to a range of 1.0%, is Cu and inevitable impurities, is heated at 1.0% until the molten metal completely solidifies.
A method for manufacturing a metal plate for a high-strength, high-conductivity lead frame, which comprises casting at a surface cooling rate of 00° C./second or more, followed by cold rolling and heat treatment at least once each. 2. The method of manufacturing a metal plate for a high-strength, high-conductivity lead frame according to claim 1, wherein Cu plating is applied after final cold rolling or heat treatment.