JPH0775252B2 - Lead frame material manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a material of a lead frame used for manufacturing an integrated circuit device, and more particularly, to a lead frame material capable of directly bonding a wire without interposing a plating layer. Manufacturing method.

"Prior Art" A general lead frame is manufactured by punching and forming a plate material made of copper or a copper alloy, and further, gold or silver plating is applied to a portion for wire bonding. The reason why the gold (silver) plating is applied is that the gold or copper wire cannot be joined with sufficient strength in the state where the metal plate is punched and formed.

However, since the quality of the plating has a great influence on the wire bonding, extremely high accuracy is required when plating the lead frame material, and the productivity is low, and the precious metal is used even if it is a minute amount. It had the drawback of being expensive.

Therefore, from the viewpoint that it is possible to significantly reduce the cost if wire bonding can be directly performed on the lead frame material without applying gold (silver) plating, for example, Japanese Patent Publication No. 62-46071.
In the publication, the surface roughness of the lead frame material made of copper or copper alloy is 0.5 μm or less at the maximum height (Rmax), and the single area of precipitates or inclusions appearing on the surface is 3 × 10 5. It has been proposed that direct bonding of gold wires is possible by setting the ^{thickness to -6} mm ² or less.

"Problems to be solved by the invention" However, as a result of actual experiments conducted by the present inventors, Rmax
Is less than 0.5 μm and the single area of precipitates or inclusions appearing on the surface is less than 3 × 10 ^-6 mm ² , the wire joining does not always go well and sufficient joining strength cannot be obtained. It turned out to be. Further, it is described in the above-mentioned publication that "it is possible by selecting the workability of rolling and the annealing conditions" to reduce the single area of the precipitates and inclusions to 3 × 10 ^-6 mm ² or less. However, it turned out that it was more difficult than expected and the manufacturing cost was high.
The precipitates present on the surface of the lead frame material are
Mainly intermetallic compounds such as FeP, while inclusions are Zr,
Oxides such as Cr, Si and Al are mainly used.

Therefore, the present inventors have investigated these precipitates and inclusions in more detail, and have obtained the following new knowledge that can supplement the drawbacks of the conventional products.

That is, the single area itself of the precipitates or inclusions is not extremely miniaturized as in the above publication, and even when the single area of these precipitates or inclusions is relatively large, these are treated with an acid or the like. Are dissolved and removed by, and a large number of fine recesses are formed on the traces. When a large number of minute recesses are formed on the surface of the lead frame material in this way, when the wire is pressure-welded by a known bonding method, the wire bonding portion penetrates into the recess and bites into the recess, resulting in extremely high bonding strength. Of.

The present inventors further conducted a detailed study on the size of the recesses and found that particularly good bonding strength was obtained in the case of 1 to 3000 × 10 ⁻⁸ mm ² . The numerical value of 3000 × 10 ⁻⁸ mm ² which is the upper limit area in this case corresponds to 10 times the upper limit of the area in the above publication.

"Means for Solving the Problems" The present invention has been made based on the above findings, and is formed of a material selected from zircon copper, iron-containing copper, and tin-containing copper, and inclusions or precipitates are exposed on the surface. And the amount of deformation is 1 to 5% by using a rolling roll whose surface is an extremely smooth surface with Ra: 0.12 μm or less.
A surface smoothing step of making the surface roughness of the plate material Ra: 0.15 μm or less by performing light rolling for finishing so that
Before or after the surface smoothing step, by dissolving and removing the inclusions and precipitates from the surface of the plate material, the opening area on the surface of the plate material is 1 ~ 3000 × 10 ^-8 mm
^The method is characterized by further comprising a porosification step of forming ^two concave portions at a distribution density of 500 to 10,000 / mm ² .

Hereinafter, the present invention will be described in detail.

As the material of the lead frame material used in the present invention, zircon copper, iron-filled copper, tin-filled copper, etc. similar to the conventional ones are used. In particular, C1 having a high content ratio of Zr etc. and easily generating inclusions
5000, C15100, C19400 and the like, which easily generate precipitates such as FeP, are suitable (these are all CDA numbers).

Then, first, this plate material is formed into a thickness of, for example, about 0.3 mm by a normal rolling process, then subjected to a normal finish rolling to a size of about 0.26 mm, and then buffed or the like if necessary. Next, with a rolling roll whose surface is an extremely smooth surface,
A light load is applied to the plate material for finish light rolling. The surface roughness required for this rolling roll is Ra: 0.12 μm or less, and the load during finishing light rolling is 1 to 1
It is desirable to set it to about 5%.

If the surface of the rolling roll is rougher than the above range, the surface roughness of the plate material will be Ra: 0.15 no matter how the deformation amount by rolling is set.
Does not fall below μm. Further, if the deformation amount of the plate material is less than 1%, the surface roughness of the plate material cannot be sufficiently increased even if the surface roughness of the rolling roll is sufficiently small. Conversely, if the deformation amount of the plate material is greater than 5%, The concave portions existing on the surface of the rolling roll are transferred to the surface of the plate material as convex portions, which not only lowers the surface roughness, but also causes surface hardening due to processing strain on the surface of the plate material to deteriorate the wire bonding system.

By the above light finishing rolling, the center line average roughness (Ra) of the lead frame material is smoothed to 0.15 μm or less. This value is 0.
If it is larger than 15 μm, a minute gap is apt to be formed between the wire bonding portion and the lead frame surface, and the bonding strength is lowered.

Next, the plate material after finishing light rolling is immersed in a treatment liquid to dissolve and remove precipitates such as FeP and the like existing on the surface and inclusions such as oxides of various metals. To form. As the processing liquid, a chlorine-based processing liquid such as ferric chloride or a fluorine-based processing liquid such as hydrofluoric acid is used. The opening area of each of the recesses is 1 to 3000 × 10 ⁻⁸ mm ² by selecting the rolling conditions described above.
It is said that If the recess is smaller than the above range, the wire bonding portion cannot be caught, and the effect of improving the bonding strength cannot be obtained. On the other hand, if it is larger than the above range, the wire biting into the recess is not stable, and the joint strength is also reduced. Also, the distribution density of the recesses on the surface of the lead frame material is 500 to 100.
It is desirable that it is about 00 pieces / mm ² , and if it is less than that, the biting is insufficient and the effect of improving the joint strength cannot be obtained.
If it is too large, the bonding strength will not be stable. Furthermore, it is desirable that the shape of the recess be a relatively deep vase shape depending on the selection of rolling conditions and the like.

According to the method for manufacturing a lead frame material having the above configuration, in the surface smoothing step, the surface of the plate material is smoothed to Ra: 0.15 μm or less while preventing surface hardening of the plate material, while in the porosification step, the plate material is By dissolving and removing the inclusions and precipitates exposed on the surface of the plate, it is possible to form relatively deep minute recesses corresponding to the particle shape of the inclusions on the surface of the plate material. When wire bonding is performed on the surface of the lead frame material obtained in this way, the wire is bonded to the flat part that is the base of the lead frame material surface with almost no gap, and moisture enters into the gap between them to improve the wire bonding strength. It is possible to prevent problems such as lowering, and at the same time, the wire material is plastically deformed and locally bites into the deep minute recesses that occur in some flat parts, so the anchor effect allows wire bonding to a simple flat surface. When the above is performed, a higher bonding strength can be obtained.

Even if a deep minute recess is formed on the surface of the lead frame material by dissolving and removing inclusions, the surface roughness Ra: 0.1
If it is less than 5 μm, it becomes difficult to penetrate the wire material deep enough into the minute recesses due to plastic deformation, and not only a sufficient anchoring effect cannot be obtained, but also the bonding strength decreases due to the penetration of moisture as described above. May occur.
On the contrary, no matter how good the surface roughness of the lead frame material is, a good anchoring effect cannot be obtained without the fine recesses, and the wire bonding strength is reduced. That is, the wire bonding property is remarkably improved only by combining the surface smoothing step for making the surface roughness of the lead frame material Ra: 0.15 μm or less and the porosification step for forming the minute recesses on the surface of the lead frame material. It becomes possible.

Furthermore, in the method of the present invention, since it is not necessary to extremely reduce the single area of precipitates and inclusions as in the conventional method, there is no need for complicated treatment, and there is an advantage that the manufacturing cost can be reduced accordingly. can get.

In the above-mentioned examples, the finish light rolling was performed and then the precipitates and inclusions were dissolved. However, the order may be reversed, and other treatments may be performed before and after these treatments as necessary. May be added.

"Example" Next, the effect of the present invention will be demonstrated with reference to an example.

Six lead frame materials of 0.255 thickness x 25.4 width x 200 mm length were formed from a C15100 (CDA number) copper alloy plate by ordinary rolling.

Next, surface roughness Ra: 0.07, 0.09,
Finishing light rolling was performed with a total deformation amount of 0.11 μm and a deformation amount of 2% using three types of surface smoothing rolling rolls (Examples 1, 2, and
3). Further, these were immersed in a solution containing 5 wt% ferric chloride and 10 wt% hydrochloric acid at 25 ° C for 1 minute to completely dissolve the precipitates and inclusions exposed on the surface.

On the other hand, as a comparative example, Ra: 0.12 but no precipitates or inclusions were removed (Comparative Example 1), or a precipitate or inclusions were removed but Ra did not satisfy the conditions of the present invention. (Comparative Example 2) and Ra: 0.34 with no precipitation removed (Comparative Example 3) were prepared.

Then, the surface roughness of all the lead frame materials was measured by a surface roughness meter or the like, and the size, distribution density, and shape of the recesses on the surface were measured using a scanning microscope.

Next, these lead frame materials were set in an automatic wire joining device, and actual wire bonding was performed. The conditions are shown below.

Joining method: Thermosonic method Wire material: Gold Wire diameter: 25μm Lead frame: Temperature: 225 ℃ Joining load: 40g Ultrasonic output: 0.25W Ultrasonic wave generation time: 20msec. After that, pull up the joined wire with a hook The pulling load required to cut the wire was measured.
At the same time, the joint strength was evaluated. This evaluation is "○" when there is no change until the wire is cut at the bonded part up to the wire pulling load, "△" when the wire is cut after the bonded part is partially peeled off, What was completely peeled off is "x". The results are shown in the table below. In the table, Examples 1 to 3 are Examples and ratios 1 to 3 are Comparative Examples.

As described above, in the method for manufacturing a lead frame material according to the present invention, in the surface smoothing step, the surface of the plate material is smoothed to Ra: 0.15 μm or less while preventing surface hardening of the plate material, while the porosification step is performed. Then, by dissolving and removing the inclusions and precipitates exposed on the surface of the plate material, it is possible to form relatively deep minute recesses corresponding to the particle shape of the inclusions. When wire bonding is performed on the surface of the lead frame material obtained in this way, the wire is bonded to the flat part that is the base of the surface of the lead frame material with almost no gap, and moisture enters into the space between them to improve the wire bonding strength. You can prevent problems such as lowering, at the same time
Since the wire material plastically changes and bites locally in the deep minute recesses that occur in flat parts, the anchoring effect provides a bonding strength higher than that when wire bonding is performed on a simple flat surface. It is possible to significantly improve the reliability of direct joining. In particular, in the present invention, since a material selected from zircon copper containing a large amount of inclusions and precipitates, iron-containing copper and tin-containing copper is used as the plate material, the surface area of the plate material has an opening area of 1 to 3000 × 10. ^-8 mm ² recesses can be formed with a distribution density of 500 to 10000 / mm ^{2 and} the anchor effect can be made even more effective. Further, since it is not necessary to extremely reduce the single area of precipitates and inclusions, complicated processing is not required,
There is also an advantage that the manufacturing cost can be reduced.

Claims (1)

[Claims] 1. A step of preparing a plate material formed of a material selected from zircon copper, iron-containing copper, and tin-containing copper and having inclusions or precipitates exposed on the surface, and the plate material having a surface of Ra: Surface that makes the surface roughness Ra: 0.15 μm or less by performing light finishing rolling so that the deformation amount is 1 to 5% using a rolling roll having an extremely smooth surface of 0.12 μm or less. Smoothing step, before or after the surface smoothing step, by dissolving and removing the inclusions and precipitates from the surface of the plate material, on the surface of the plate material, the opening area is 1 ~ 3000 × 10 ^-8 mm
^2. A method of manufacturing a lead frame material, which comprises a step of forming a number of recesses of ^{2 at} a distribution density of 500 to 10000 / mm ² .