JP3336802B2 - Lead frame cladding material and lead frame manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a lead frame in which an inner lead is connected to an end of the outer lead through an etching stop made of another metal material, and is preferably used for this manufacturing. And a clad material for a lead frame.

[0002]

2. Description of the Related Art As a lead frame, for example, as shown in FIG. 3, an outer lead 1 made of copper, an etching stop portion 2 made of aluminum formed on the base surface thereof, and a copper connected to the etching stop portion 2 are formed. And a thin inner lead 3 made of aluminum and a bump 4 made of aluminum or the like formed at the tip of the inner lead 3 are known. This lead frame is usually used by bonding to the electrode pads 6 of the semiconductor chip 5 via the bumps 4 and sealing the semiconductor chip 5 with a sealing resin 7.

In manufacturing such a lead frame, conventionally, as shown in FIG. 4, a thick outer lead copper layer 8 and an etching stop aluminum layer 9 are formed.
A method is known in which a three-layered clad material 11 in which a thin copper layer 10 for an inner lead is laminated with a thin layer is used and etched. That is, the lead frame is manufactured by selectively etching the outer lead copper layer 8 and selectively etching the inner lead copper layer 10 with respect to the clad material 11. By providing the etching stop aluminum layer 9 in this manufacturing, the erosion of the outer leads due to the etching for the inner leads and the erosion of the inner leads due to the etching for the outer leads are respectively prevented.

However, in such a conventional lead frame, since the patterning of the inner leads 3 must be formed by one-sided etching in the manufacture thereof, it is possible to avoid an increase in the amount of side etching. Therefore, there is a problem in that the fine pitch of the inner lead 3 is limited, and the demand for ultra-high integration cannot be sufficiently satisfied. That is, conventionally, the width of the inner lead and the interval between the inner lead are set to 7
Although it was about 5 μm, the width and spacing of the inner leads have to be reduced to about 35 μm in accordance with the ultra-high integration, but in order to cope with this, the conventional method of forming the inner leads by etching has It is extremely difficult in the process.

In recent years, in order to solve such a problem, the inner lead copper layer 10 of the clad material 11 is not etched to directly form the inner leads 3. A method of forming inner leads by electroplating copper on the copper layer 10 is provided. In such a method, the copper layer 10 for the inner lead of the clad material 11 functions as an adhesion layer for improving the adhesion to the inner lead when the inner lead is deposited thereon by electrolytic plating. are doing.

[0006]

However, in the method of forming an inner lead by further plating copper on the inner lead copper layer 10 as described above, when the inner lead is electrolytically plated, a deposit is formed by electrolytic plating. An abnormal precipitation portion is easily formed on the inner lead thus formed. Also, an aluminum layer 9 for etching stop
However, since most of the aluminum layer 9 is removed by etching, the thickness cannot be increased more than necessary in terms of cost and etching process. Layer 8
Is selectively etched, the aluminum layer 9 does not sufficiently function as a barrier (etching stop layer), and as a result, manufacturing defects such as disconnection or chipping are likely to occur in the inner lead on the side opposite to the outer lead copper layer 8. Has become. In addition, since manufacturing defects are liable to occur in this manner, the present situation is that manufacturing costs are high due to low yield, and thus prevention of manufacturing defects as described above is desired. It is.

The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent abnormal deposition when an inner lead is formed by electrolytic plating, and furthermore, in an etching process when forming an outer lead. An object of the present invention is to provide a method for manufacturing a lead frame which does not adversely affect inner leads, and a lead frame clad material suitably used for the method.

[0008]

Means for Solving the Problems As a result of earnest studies to solve the above-mentioned problems, the present inventors have presumed that the abnormal precipitation is caused by the following causes. A local battery is formed between the aluminum layer 9 and the inner lead copper layer 10 in the clad material 11 between the layers 9 and 10 due to, for example, a small amount of moisture remaining between the layers. Pinholes are formed in the layers 9 and 10, or pinholes are formed for reasons other than local cell formation. The formation of such pinholes causes the abnormal precipitation.

Further, it was presumed that the manufacturing defect of the inner lead during the selective etching of the outer lead copper layer 8 was caused by the following causes. In addition to the formation of the pinholes for the reasons described above, prior to the selective etching process for forming the outer leads, the process from the side of the inner lead copper layer 8 in the process of forming the inner leads (for example, electrolytic plating for forming the inner leads) Process and pre-process), a pinhole is also formed in the copper layer 10 for the inner lead and the aluminum layer 9 therebelow due to these processes. In this case, the aluminum layer 9 and the inner lead copper layer 10 do not sufficiently function as a barrier (etching stop layer). As a result of various improvements of the clad material based on such estimation, the inventors have found that the following structure can solve the above-mentioned problems and can form an inner lead well, and have completed the present invention.

That is, in the lead frame clad material according to the first aspect of the present invention, a plate-shaped metal base serving as an outer lead forming member, and a metal material different from the metal base on one surface of the metal base. Etched stop layer, the metal base on the etch stop layer, a barrier layer formed of a metal material different from the etch stop layer, formed on the barrier layer, the inner lead by electrolytic plating An object of the present invention is to provide an adhesive layer for improving the adhesion to the inner lead during the deposition.

According to a fourth aspect of the present invention, in the method of manufacturing a lead frame, a plating mask layer having a negative pattern with respect to an inner lead to be formed is formed on the adhesion layer of the lead frame cladding material. Forming an inner lead by plating on the adhesion layer using the plating mask layer as a mask, forming an outer lead in a region where the outer lead of the metal base is disposed, and A step of etching the back side of the region where the inner lead is provided, a step of etching the etching stop layer, a step of etching the barrier layer, and a step of etching the adhesion layer. This was the solution to the problem.

[0012]

According to the cladding material for a lead frame of the present invention, a barrier layer made of a metal material different from the etching stop layer is provided between the etching stop layer and the adhesion layer. The barrier layer
If there is an ionization tendency between the ionization tendency of the metal forming the etching stop layer and the ionization tendency of the metal forming the adhesion layer, that is, if the ionization column is formed by a metal located therebetween, the etching stop layer and the adhesion layer A local battery is prevented from being formed between the barrier layer and the etching stop layer, or even if a local battery is formed between the barrier layer and the adhesion layer, the etching stop layer The electromotive force is smaller than that of the local battery formed between the contact layer and the contact layer, and therefore, the formation of pinholes in the etching stop layer and the like is suppressed as compared with the related art. Further, since the barrier layer is formed between the adhesion layer and the etching stop layer, even if a pinhole or the like is formed in the adhesion layer due to processing from the adhesion layer side such as an inner lead forming step. Also, the barrier layer functions as a layer for protecting the etching stop layer, thereby preventing pinholes from being formed in the etching stop layer.

According to the method for manufacturing a lead frame of the present invention, the lead frame is manufactured using the clad material for a lead frame according to the first aspect.
Due to the formation of pinholes in the etching stop layer or the like of the cladding material for the lead frame, abnormal deposition at the time of forming the inner lead and defective production of the inner lead at the time of selective etching at the time of forming the outer lead. Is prevented.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 (a) is a perspective view of an essential part showing an embodiment of a clad material for a lead frame according to the present invention. In FIG. 1 (a), reference numeral 20 denotes a clad material for a lead frame (hereinafter abbreviated as a clad material). ). The clad material 20 includes a plate-shaped metal base 21, an etching stop layer 22 formed on one surface of the metal base, a barrier layer 23 formed on the etching stop layer 22, And a contact layer 24 formed on the metal base 20. At a predetermined position on the metal base 20, there are formed three layers of an etching stop layer 22, a barrier layer 23, and a contact layer 24 having a much smaller area. It is configured by forming a large number of laminated portions.

The metal base 21 is made of copper, copper alloy or 4
It is a plate made of two alloys and having a thickness of about 150 μm, and serves as a member for forming outer leads of a lead frame. The etching stop layer 22 is made of aluminum as in the conventional case, and has a thickness of 1.0 μm.
m to 5.0 μm. Barrier layer 2
Reference numeral 3 is made of chromium and has a thickness of 0.1 μm to 0.2 μm. The adhesion layer 24
It is made of copper as before, and has a thickness of 1.0 μm.
To 2.0 μm.

In order to manufacture such a clad material 20, for example, a Cu alloy (trade name: TAMAC-15 material, manufactured by Mitsubishi Shindoh Co., Ltd.) having the above thickness is prepared as the metal base 21, and its surface layer is deposited. 12 nm by ion beam method
After cleaning by etching to a certain extent and removing the surface oxide film, aluminum (Al), chromium (Cr), copper (Cu) is placed at a predetermined position by sputtering or the like.
Is performed in this order to form the etching stop layer 22, the barrier layer 23, and the adhesion layer 24 having the thicknesses in the above ranges.

Here, the reason why chromium is used as the barrier layer 23 is that, in the ionization sequence (ionization tendency), the chromium is used as aluminum to become the etching stop layer 22;
Although it is located between the copper serving as the adhesion layer 24, and furthermore, the deposition process is easy in the manufacturing process, and the adhesion between the aluminum and the copper is relatively good.
The most significant reason is that the lead frame was manufactured using the clad material 20 in which the barrier layer 23 was actually formed of chromium, and the empirical reason that the yield of the lead frame could be remarkably increased as compared with the conventional case. is there.

The reason why the thickness of the etching stop layer 22 is changed from 1.0 μm to 5.0 μm is that if the thickness is less than 1.0 μm, a pinhole is formed during vapor deposition. Base 2
When forming outer leads by selective etching of 1,
This is because the function of protecting the inner lead side cannot be sufficiently secured. If the thickness exceeds 5 μm, the cost is disadvantageous, and the etching stop layer 22
This is because when etching is removed, a loss in manufacturing increases due to an increase in etching time and the like.

The thickness of the barrier layer 23 ranges from 0.1 μm to 0.1 μm.
When the thickness is set to 2 μm, as in the case of the etching stop layer 22, if the thickness is less than 0.1 μm, the function as a barrier layer is not sufficiently exhibited. This is because the loss of time increases. However, since the barrier layer 23 functions only as an auxiliary to the etching stop layer 23, it is sufficient that the barrier layer 23 is much thinner than the etching stop layer 22 as described above. It performs its function in the first place.

The thickness of the adhesion layer 24 is set to 1.0 μm to 2.0 μm.
When the thickness is less than 1.0 μm, pinholes are formed at the time of vapor deposition, and the adhesion to the inner lead formed thereon by the electrolytic plating method is not sufficiently ensured, which may cause abnormal deposition. If the thickness exceeds 2.0 μm, the etching time will be long when the adhesion layer 24 is finally removed by etching.
This is because it is difficult to control the etching process described later due to the use of the same material as the inner lead to be formed.

Next, an embodiment of the manufacturing method according to claim 4 of the present invention will be described based on a manufacturing method of a lead frame using the clad material 20 having such a structure. First, the clad material 20 shown in FIG. 1A is prepared, and then a dry film (not shown) is adhered to the inner lead forming portion on the adhesion layer 24, and the exposure film prepared beforehand is applied to the dry film. A known exposure and development process is performed using a mask to form a negative pattern on the inner lead to be formed, thereby obtaining a plating mask layer according to the present invention.

Then, after the pattern is formed, a degreasing treatment is performed if necessary, and the surface of the adhesion layer 24 is activated with sulfuric acid or the like, followed by copper sulfate plating.
As shown in (b), inner leads 25 made of copper are formed on the adhesion layer 24 on the surface of the barrier layer 23. For copper sulfate plating, specifically, CuSO ₄ is used as a plating solution.
g / l, H ₂ SO ₄ 200 g / l, Cl ⁻ ion 5
And a current density of 1.0 to 4.0 A /
Electroplating is performed at about dm ² . The inner leads 25 formed in this manner have a line width of 3
About 5 μm, spacing between leads is about 35 μm, thickness is 3
It is about 0 μm. Here, as shown in FIG. 1B, the base end of each inner lead 25 protrudes outward from the adhesive layer 24 (that is, the etching stop layer 23), and is directly bonded to the metal base 21. Form.

After the inner leads 25 are formed in this manner, the dry film (plating mask layer) is removed, and if necessary, a reinforcing tape (not shown) is provided on the surface of the inner leads 25. The inner leads 25 are reinforced by bonding in the crossing direction. In the process of forming the inner leads 25, etc., the chemical bonding of the barrier layer 23 under the adhesive layer 24 and on the etching stop layer 22, although various chemicals attack the adhesive layer 24 side chemically. Is provided, so that a pinhole is prevented from being formed in the etching stop layer 22.

Next, a resist pattern (not shown) is formed on the back surface of the metal base 21, that is, on the surface opposite to the side on which the inner leads 25 are formed. By selectively etching the metal base 21 using an etching agent,
The outer leads 26 are formed as shown in FIG.
At the same time, the metal base 21 is also selectively etched away on the back side N of the portion where the inner leads 25 are formed first. At this time, inner lead 2
5 on the back side, the adhesion layer 24 and the barrier layer 2 made of chromium
3. Since the etching stop layer 22 made of aluminum is formed, the inner leads 25 are protected without being damaged by the selective etching process.

In the etching of the N portion on the back side of the inner lead 25..., Not all the portions corresponding to the etching stop layer 22 formed thereon are removed, but the outer peripheral portion of the etching stop layer 22. Is performed so as to leave a portion corresponding to the predetermined width as it is. Therefore, the patterns of the outer leads 26 are formed such that the portions corresponding to the remaining portions of the etching stop layer 22 are part of the outer leads 26.

Next, after the metal base 21 is removed by etching in this manner, the etching stop layer 22 exposed on the back side N of the location where the inner lead is formed is removed by etching. It is necessary to perform this etching so as to erode aluminum and not to erode the outer leads 26 and the inner leads 25. For example, when performing wet etching, a phosphoric acid-based etchant is used. When dry etching is performed, BCl ₃ (40 SCCM) + Cl ₂ is used as an etching gas.
(100 SCCM) + He or N ₂ (1500 SCC
M), RF power is 220W, pressure is 1340P
a, table temperature 5 ° C., etching rate 7 μm / 240
This is performed by reactive ion etching under conditions such as sec.

Thus, the etching stop layer 22
Is etched, the barrier layer 23 on the back side of the etching stop layer 22 is simultaneously removed because its thickness is sufficiently smaller than that of the etching stop layer 22. However, it goes without saying that the etching is performed for a longer time than before. As described above, in a predetermined portion of the outer peripheral portion corresponding to a portion where the metal base 21 remains without being removed, neither the etching stop layer 22 nor the barrier layer 23 partially remains without being removed. The remaining portion becomes the etching stop portion 2 shown in FIG.

Thereafter, the adhesion layer 24 exposed also on the side opposite to the inner leads 25... Due to the removal of the etching stop layer 22 is formed by using an etching agent composed of, for example, a hydrogen peroxide solution, sulfuric acid and hydrofluoric acid. This is removed by etching so that the adjacent inner leads 25 are completely separated from each other. (Of course, after the resin is sealed, the diver portion 26a of the outer lead 26 is short-circuited until the unnecessary portion of the outer lead is cut.) In the etching here, the inner layer 24 is formed by the inner layer. Since it is made of copper like the lead 25, it is difficult to selectively remove only the adhesion layer 24 by etching. Therefore, the difference in thickness (the inner lead 25 is about 30 μm, and the adhesion layer 24 is 1.0 to 1.0 μm).
2.0 μm) to etch them simultaneously.
The adhesion layer 24 is surely removed and the inner leads 25
For example, a method is adopted in which the etching is terminated when a sufficient thickness of about 25 μm is left. Then, bumps (not shown) are formed on the distal end surfaces of the inner leads 25 by aluminum sputtering, photoetching, or the like, to obtain a lead frame having a configuration as shown in FIG.

In such a method of manufacturing a lead frame, a cladding material 20 is provided with a barrier layer 23 made of chromium between an etching stop layer 22 made of aluminum and an adhesion layer 24 made of copper. The following effects can be obtained by using. Since the ionization tendency of chromium forming the barrier layer 23 is located between aluminum forming the etching stop layer 22 and copper forming the adhesion layer 24, the etching stop layer 2
2 and the adhesion layer 24 can be prevented from being formed, and between the barrier layer 23 and the etching stop layer 22, or between the barrier layer 23 and the adhesion layer 24. Even when a local battery is formed, the electromotive force is smaller than that of the local battery formed between the etching stop layer 22 and the adhesion layer 24, and therefore, the formation of a pinhole in the etching stop layer 22 and the like is smaller than that in the related art. Thus, abnormal deposition of the inner lead 25 caused by the pinhole can be prevented.

Further, since the barrier layer 23 is formed between the adhesion layer 24 and the etching stop layer 22, the barrier layer 23 forms the etching stop layer 22 during processing from the adhesion layer 24 side such as an inner lead forming step. By functioning as a protective layer, the etching stop layer 22
Pinholes can be prevented from being formed in the
Therefore, it is possible to prevent the manufacturing defect of the inner lead during the selective etching at the time of forming the outer lead.

Also, since the inner leads 25 are formed such that the base ends thereof are in contact with the metal base 21, the obtained lead frame is formed of the outer leads 2.
6 and the inner leads 25 are directly connected. Accordingly, in this lead frame, the bonding strength between the outer leads 26 and the inner leads 25 is increased, and a potential difference is not generated between them. Therefore, a semiconductor chip is mounted on the lead frame. When used as an IC after being sealed with a resin, even if moisture penetrates into the sealing resin due to aging, even if moisture enters the sealing resin, the inner leads 25 and / or the outer leads 26 and the etching stop portion (etching stop layer 22) may be in contact with each other. A local battery is formed in between, thereby preventing the disadvantage that corrosion of the etching stop portion is promoted.

In the above-described embodiment, the negative pattern of the inner lead was formed by a dry film prior to the formation of the inner lead. For example, instead of this, a resist such as an electrodeposition resist (oligo EC-UV manufactured by Nippon Chemical Petroleum) may be used. A plating resist layer may be formed using a material, and a known pattern may be formed by subjecting the layer to a known exposure and development process to form a plating mask layer according to the present invention.

(Experimental example) Aluminum, chromium, and copper were sequentially deposited on a square copper metal base to have a thickness of 1.3.
etching stop layer made of aluminum with a thickness of 0.2 μm, barrier layer made of chromium with a thickness of 0.2 μm, thickness of 2.0 μm
Each of the adhesion layers made of copper is formed as shown in FIG.
Eight clad members having the layer structure of the present invention shown in FIG. Separately, aluminum and copper are sequentially deposited on the same metal base as the above-mentioned metal base to have a thickness of 1.3.
forming an etching stop layer made of μm aluminum and an adhesion layer made of copper having a thickness of 2.0 μm,
Six cladding materials having a conventional layer configuration were produced.

As shown in FIG. 2, the adhesion layer surfaces of the respective cladding materials obtained in this manner are arranged in the order of A region, B region from the center side.
The area and the C area were potted to the A area serving as the I / L center exposed portion and the C area serving as the ball grid area, and no potting was applied to the B area serving as the polyimide tape area. Note that potting was performed by hand coating. Next, a resist pattern was formed on the metal base surface of each clad material, and thereafter, the metal base was selectively etched using an etching agent composed of a hydrogen peroxide solution and sulfuric acid. The number of pinholes of the etching stop layer (aluminum layer) exposed by the etching of each clad material after the etching treatment was visually counted from an electron microscope photograph.

In the clad material of the present invention, in each of the A region, the B region and the C region, only about 14 to 70 pinholes were generated in each region. On the other hand, in the conventional clad material, more than 150 pinholes are generated in all the regions in three out of the six clad materials, and more than 150 pinholes are formed in the A region and the C region in the remaining three clad materials. Had occurred. Therefore, it was confirmed that the occurrence of pinholes of the product of the present invention was reduced to 1/3 to 1/20 of that of the conventional product. From these results, it was found that the product of the present invention in which the barrier layer was formed was able to significantly reduce manufacturing defects caused by pinholes as compared with the conventional product.

[0036]

As described above, in the clad material for a lead frame according to the first aspect of the present invention, a barrier layer made of a metal material different from the etching stop layer is provided between the etching stop layer and the adhesion layer. For example, if the barrier layer is formed of a metal having an ionization tendency between the ionization tendency of the metal forming the etching stop layer and the metal forming the adhesion layer, the etching stop layer By preventing local cells from being formed between the adhesion layer and the like, it is possible to suppress the formation of pinholes in the etching stop layer, etc., as compared with the conventional method, thereby preventing abnormal deposition during inner lead deposition. To reduce manufacturing defects,
The manufacturing cost can be reduced by increasing the yield. In addition, a barrier layer is formed between the adhesion layer and the etching stop layer, and the barrier layer functions as a layer for protecting the etching stop layer during processing from the adhesion layer side such as an inner lead forming step. In this process, it is possible to prevent a pinhole from being formed in the etching stop layer in this process, thereby preventing a manufacturing defect of the inner lead at the time of selective etching at the time of forming the outer lead and reducing a manufacturing defect,
The manufacturing cost can be reduced by increasing the yield.

The method for manufacturing a lead frame according to the present invention is a method for manufacturing a lead frame using the cladding material for a lead frame according to claim 1, so that the etching stop layer of the cladding material for the lead frame is used during the manufacturing. It is possible to prevent abnormal deposition at the time of forming the inner lead and defective manufacturing of the inner lead at the time of selective etching at the time of forming the outer lead due to the formation of pinholes at the same time. Higher cost can be reduced.

[Brief description of the drawings]

FIG. 1 (a) is a perspective view of an essential part showing one embodiment of a clad material of the present invention, and FIGS. 1 (b) and 1 (c) show a production method of the present invention using the clad material shown in FIG. 1 (a). FIG. 6 is a manufacturing process diagram for explaining one embodiment.

FIG. 2 is a plan view of a clad material for showing a potting region.

FIG. 3 is a side sectional view showing an example of a lead frame.

FIG. 4 is a side sectional view showing an example of a conventional three-layer clad material.

[Explanation of symbols]

 Reference Signs List 20 clad material for lead frame 21 metal base 22 etching stop layer 23 barrier layer 24 adhesion layer 25 inner lead 26 outer lead

Claims (4)

(57) [Claims] 1. A plate-shaped metal base serving as an outer lead forming member; an etching stop layer formed on one surface of the metal base from a metal material different from the metal base; A metal base, a barrier layer formed of a metal material different from the etching stop layer, and a good adhesion between the inner lead and the inner lead when the inner lead is deposited and formed by electrolytic plating on the barrier layer. A cladding material for a lead frame, comprising: 2. The clad material for a lead frame according to claim 1, wherein the metal base is made of copper or a copper alloy, the etching stop layer is made of aluminum, the barrier layer is made of chromium, and the adhesion layer is copper. A cladding material for a lead frame, comprising: 3. The cladding material for a lead frame according to claim 2, wherein the etching stop layer has a thickness of 1.0 μm to 5.0 μm.
The barrier layer is formed to a thickness of 0.1 μm to 0.5 μm, and the adhesion layer is formed to a thickness of 1.0 μm to 2.0 μm. A clad material for a lead frame, characterized by the following. 4. A plate-shaped metal base serving as an outer lead forming member; an etching stop layer formed on one surface of the metal base from a metal material different from the metal base; A metal base, a barrier layer formed of a metal material different from the etching stop layer, and formed on the barrier layer to improve the adhesion between the inner lead and the inner lead when the inner lead is formed by electrolytic plating. A method for manufacturing a lead frame using a lead frame clad material comprising an adhesion layer for forming a lead frame, comprising: a negative pattern with respect to an inner lead to be formed on the adhesion layer of the lead frame clad material. Forming a plating mask layer; and plating the inner surface by plating on the adhesion layer using the plating mask layer as a mask. Forming an outer lead in a region where the outer lead of the metal base is disposed; and etching away a back side of a region where the inner lead is disposed of the metal base. A method of manufacturing a lead frame, comprising: a step of etching the etching stop layer; a step of etching the barrier layer; and a step of etching the adhesion layer.