JPH03138038A - Method for removing residual strain of lead frame material - Google Patents

Abstract

PURPOSE:To reduce the residual strain of an edge part and to improve the yield by leveling strip stock for the lead frame of an IC through a tension leveler, giving a plastic elongation in the lengthwise direction and uniformizing the residual stress in the width direction. CONSTITUTION:A tension leveler 2 is provided to pass a sheet 1 between at least two stage rolls 2A, 2B equipped so that points of application of the rolls cross each other little by little to the advancing direction of the sheet 1 and to give at least two times of bending in the opposite direction to remove the warp. The tension leveler 2 need not have a multistage roll but one push operation is desired to be performed at least by two stage rolls 2A, 2B. At this time, since it is not easy that a quantity of plastic elongation is calculated accurately, it is necessary to control the condition of operation using a tension and an amount of push giving to the strip stock 1 between driving rolls 3, 4 as parameters.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention substantially eliminates residual distortion in a band-shaped material used for an IC lead frame, or at least reduces it to a level that does not cause any practical problems. Regarding the method.

[Prior Art] A typical IC lead frame material is a product obtained by applying M cladding to a band of a low thermal expansion metal such as 42N1 alloy. The process of manufacturing an IC using this clad strip includes the following steps: blanking, bending into a shape, washing and sweating, sealing the ceramic base, mounting, sealing with Ag wire bonding, and plating. Become.

However, the blank that has gone through the above bending process has a saddle shape.
In other words, when viewed from the side, the upper part must be distorted in a concave manner, or conversely, in a convex manner.

This involves processes such as rolling, slitting, and cladding that lead to the production of clad strips, mainly through rolling.
This phenomenon is caused by residual stress applied to the edges of the material. If the residual stress at the edge is compressive, the edge will stretch due to the force that tries to return to its original state after the bending step, resulting in a concave shape at the top as shown above. has a convex shape.

This is evidenced by a report that the results of calculating residual stress using the so-called "removal method" were in good agreement with the results based on data actually measured using X-rays (Fujisawa et al., Plasticity and Processing, 4.1 (1964). ), 424).

If the distortion is significant, the lead frame cannot be used for II construction because it will interfere with the β-ray bonding operation.

Therefore, the lead frame material should have as little residual strain as possible.

The means traditionally employed for this purpose is annealing.
However, typical lead frame materials require l-cladding.
In addition to the constraint that AfJ must have a melting point of 660'C, 42Ni alloy strip material becomes brittle when an alloy is formed by diffusion at the joint surface of Ap and N1.
The limit is to heat it for about 1 to 2 minutes to a temperature around 'C. In this case, it cannot be expected to obtain a sufficient distortion removal effect.

[Problem to be Solved by the Invention 1] An object of the present invention is to provide a method for substantially eliminating distortion remaining in a strip material used for an IC lead frame, or at least reducing it to a limit that does not cause any practical problems. There is a particular thing.

[Means for Solving the Problems 1] The method for removing residual strain in a lead frame material of the present invention is as follows:
As shown in the figure, the strip material (1) is unwound from the coil (1A), applied to the tension leveler (2), and wound up to form a coil (1B), during which plastic elongation is applied in the longitudinal direction to form a residual window in the width direction. This consists of reducing residual distortion by making the thickness uniform. Reference numbers (3) and (4) are a pair of drive rolls for tensioning the strip, of course (4) rotating at a slightly higher feed rate than (3).

The amount of plastic elongation that should be applied varies somewhat depending on various conditions such as the quality of the strip material, rolling conditions or processing history, plate thickness, and width, but the appropriate range for each case can be easily determined through experiment. You will be able to know. It is a strip material of ρ Clad-42N1 alloy, which is a typical lead frame material, and has a thickness of 0.25 m and a width of 23.1 rM! For example, as shown in the example below, 0.2 to 0
．． A range of 5% is appropriate.

[Function] A tension leveler is a device commonly used for the purpose of correcting warpage in thin plates, and is a device that consists of at least two stages of rolls that are arranged so that the points of action of the rolls are slightly different from each other in the direction of travel of the plate. This is based on the principle that a plate is passed between the two and bent at least twice (usually 9 to 10 times) in opposite directions to eliminate warping. Warping [4] In contrast to visible deformation, residual distortion is a problem that cannot be discerned visually and has an impact on Toshitsu's processing methods.The present inventors believe that a tension leveler is useful in resolving this issue. This is the first knowledge I have gained.

In view of the above principle, the tension leveler used in the residual strain removal method of the present invention does not need to have multiple rolls unlike conventional ones, but has at least two rolls (2A and 2B>, it is sufficient that it can be pressed once.Regardless of the number of roll stages, it is not easy to accurately calculate the amount of plastic elongation given by this type of device, so in practice it is It is advantageous to control the operating conditions using parameters such as the tension applied to the strip between drive rolls (3) and (4) and the indentation (H+t/2> in FIG. 1).

(Example 1) Plastic elongation of up to 0.6% was applied to a 0.25 mm thick x 23.1 m wide strip of A and Q clad-42Ni alloy using a tensile tester and a tension leveler. ,
The degree to which the residual strain at the edge was reduced was investigated. The plastic strain when using a tension leveler was calculated according to the method described in Kashiyo et al., Sumitomo Metals 28-1 (1976) 1.

The amount of residual air distortion is 120 mm in the longitudinal direction of the above strip material.
Width of m'1. A comb-shaped specimen was created by photo-etching a pattern with a spacing of 0.35 m using Orrm.
The degree of curvature of the outermost comb teeth (ie, the part most susceptible to edge residual stress) was recorded by measuring at the free end. The size of the amount of oil in each bowl is ranked as follows, with rank A passing the test and others failing.

A: 1~2.5 m or less B: 2.5 m or less and 3.5 s or less C: 3.5 m or less 5.5! The results for M1 and below are as shown in the graph in Figure 2, and there is a slight difference between when using a tensile tester and when using a tension leveler, but it is approximately 0.2 to 0.5%.
It can be seen that the residual strain becomes smaller when elongation is applied in the range of .

(Example 2) For the same strip material as in Example 1, using a tension leveler, the indentation amount was 1.5 #, the tension was 13°8 K!J f
The residual distortion was reduced under the condition of /s2. According to the above calculation method, this condition should give a plastic elongation of about 0.5%.

Measurements were taken every 10 m over the 100 m length of the coil.
Regarding the rolling roll driving force during rolling, the test was carried out separately on the D side (drive, ie, motor side) and the W side (work, ie, the opposite side of the motor).

The results are shown in Figure 3, and it was confirmed that the residual strain was sufficiently reduced on both sides of the strip.

[Effects of the Invention] When the method of the present invention is used, residual strain at edges that tends to occur in IC lead frame materials can be effectively reduced and removed to a level that does not cause any practical problems. especially,
Ap clad-42N, a typical lead frame material
1 alloy strip, it can be carried out to great effect without the limitations associated with conventional annealing methods.

This not only improves the yield of good lead frame materials, but also facilitates IC'S construction.

[Brief explanation of the drawing]

FIG. 1 is a conceptual explanatory diagram showing the principle of the method for removing residual strain in a lead frame material according to the present invention. FIG. 2 and FIG. 3 are both graphs showing data in an example of the present invention. 1...Lead frame material 1△, 1B...Coil 2...Tension leveler 2A, 2B...Leveling roll 3.4...Tension drive roll

Claims (2)

[Claims] (1) Removal of residual strain from lead frame material by applying a tension leveler to the IC lead frame strip material to give plastic elongation in the longitudinal direction and equalizing residual stress in the width direction to reduce residual strain. Method. (2) The method according to claim 1, wherein the strip material is an Al-clad-42Ni alloy, and the plastic elongation is selected to be in the range of 0.2 to 0.5%.