JPH03283644A - Manufacture of lead frame - Google Patents

Abstract

PURPOSE:To conduct formation of a small thickness part and shape machining simultaneously and thereby to obtain easily a lead frame of high precision and high reliability with a necessary strength maintained, by forming a necessary resist pattern on each of the front and the rear of a metal strip material and by conducting etching from the front and the rear simultaneously. CONSTITUTION:A plating layer of Pd or the like is formed on the surface of a metal strip material M and an area other than the area where a small thickness part is formed is covered with a resist pattern R1, while a resist pattern R2 having an inner lead 12, a dumb bar 13, an outer lead 14, etc., is formed on the rear of the strip material M. When etching is conducted from both the front and the rear simultaneously, the small thickness part for the inner lead 12 and the shapes of the leads are formed simultaneously and a pattern being highly precise and having little undercut can be formed. Thus, a lead frame of high precision and high reliability is prepared easily with a necessary strength maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a lead frame, and particularly to a method for manufacturing a high-density lead frame.

(Prior art) Lead frames for conductor devices such as ICs and LSIs are
A plating process in which a metal strip with a thickness of 0.25 m5 or 0°15 m5 is shaped by removing unnecessary parts by either photoetching or press processing, and then plating is applied to a predetermined part, using tape. It is formed through a fixing process, etc., in which the inner leads are pasted and fixed between each other.

Incidentally, as semiconductor devices become more dense and highly integrated, the chip area and the number of lead pins increase, but packages tend to remain the same as before or become smaller.

Therefore, as the number of inner leads increases within the same area, the width of the inner leads and the distance between adjacent inner leads naturally become narrower. For this reason, problems such as deformation of the inner lead due to a decrease in strength and defects such as short circuits between the inner leads due to the deformation have become a problem.

For example, in press working, it is well known that it is desirable for lead spacing and plate thickness T to have a relationship of D≧T from the viewpoint of processing accuracy and economy.

However, in recent years, as semiconductor devices have become increasingly highly integrated, lead spacing has become smaller than the board thickness, and lead widths have also become smaller. In this way, when press punching is performed with a lead spacing that is less than the plate thickness, the pressing area becomes narrower, the compression is lowered, the inner lead and the outer lead are twisted, and residual stress remains. This tendency increases as the DOT relationship and lead width become narrower.

If residual stress remains in this manner, deformation or twisting of the leads will occur due to the influence of the residual stress during the subsequent heating and bending processes, resulting in deformation and deformation instead of the low strength mentioned above. It is easy to cause defects such as short circuit! The problem was that it was easy to use.

On the other hand, in etching processing, as the processing depth increases and the lead width becomes narrower, the influence of the undercut phenomenon becomes more pronounced, resulting in problems of reduced dimensional accuracy and strength. This phenomenon increases with machining depth and increases the corrosion coefficient F
5. When the depth is D, the opening width is W1, and the processing width (lead width) is W, it is known that the following relationship exists between these.

W −w −2D / F This equation also shows that it is desirable to reduce the depth D, that is, the plate thickness. However, when the plate thickness is reduced, the mechanical strength is reduced and it becomes difficult to support the frame. For this reason, during transportation and positioning between processes and during the J-process, damage such as bending or bending may occur due to insertion and removal of the reference bin, resulting in a problem of lowering yield and reliability of the lead frame.

Therefore, as shown in Japanese Patent Application Laid-Open No. 60-103653, the inner leads are press-worked and then coined to form a thin wall part, and the excess wall produced by coining is removed to form a thin wall part. A method of forming an inner lead has also been proposed.

However, this method not only increases manufacturing costs due to coining, but also reduces reliability and yield of the lead frame due to deformation of the inner lead tip due to residual stress caused by coining, and requires heat treatment to remove residual strain. There are problems such as

(Problems to be Solved by the Invention) As described above, with the increasing integration of semiconductor devices, the lead spacing and lead width are becoming smaller and smaller, and the increase in viscosity has become a major problem.

Therefore, it is necessary to reduce the thickness of the entire lead frame. However, when the entire lead frame is made thinner, the overall strength decreases, resulting in deformation of the lead frame during transportation, handling, and positioning.
This was the cause of low reliability and yield of conductor devices.

The present invention was made in view of the above-mentioned circumstances, and is based on Lee I.
A lead frame that maintains the required strength of the frame, is easy to manufacture, has high precision, and is highly reliable! (3% is considered [1 target.

[Structure of the invention]

(Means for Solving the Problems) Therefore, in the present invention, a resist pattern having a lead frame pattern is formed on the surface of a metal strip, and a resist pattern having an opening a in a thin portion forming area is formed on the back surface. In this state, etching is performed from both sides, so that the formation of thin parts and the shaping of inner leads, outer leads, etc. are performed at the same time.

Furthermore, before forming and shaping the thin portion, at least the inner lead and outer lead formation regions on the substrate surface are plated with Pd or Pd-Ni, and thereafter the thin portion is formed and shaped. .

(Function) According to the above configuration, since thin portions free from residual stress are selectively formed by etching from both sides and shape processing is performed at the same time, the outer frame is thick and strong, while Areas such as inner lead parts that have strict dimensional accuracy are processed starting from the thinner parts, so there are fewer undercuts and it is possible to form fine patterns with high precision.

Here, the thin wall portion is processed to have a wall thickness of about 172 times the thickness of the thick wall wall portion such as the outer frame.

Further, the thin portion is formed to include at least the inner lead portion, and may also be formed to include the dam bar and the outer lead.

In addition, if at least the inner lead and outer lead formation areas on the substrate surface are plated with Pd or Pd-Ni before forming and shaping the thin parts, then shaping can be performed as before. Since there is no need to perform post-plating, there is no adhesion of plating metal to the side surfaces of the inner leads, and it is possible to prevent the tips of the inner leads from becoming oval shaped during the plating process.

(Example) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

A lead frame formed by the method of the embodiment of the present invention is shown in FIG. 1(a) in a plan view and in FIG.
As shown in the cross-sectional view and the perspective view in FIG.
1/2 of the wall thickness of the outer area such as side par, except for 1.
It is characterized by having a degree of

That is, the inner ly r around the die pad 11:
It consists of an inner region Q1 of package lines P in which package lines P 12 are arranged radially, and an outer region Q2 in which dam bars 13, outer leads 14, side pars 15, 16, etc. are formed. Here, the support pad 17 and the die pad 11 are formed to be solid in order to strengthen the support. 18 is a polyimide tape for support.

Next, a method for manufacturing this lead frame will be explained.

First, as shown in FIG. 3(a), P is applied to the surface of the strip material M.
d or Pd-Ni plating (not shown)
After forming, the area on the back side of the strip material M except for the inner lead 12 forming area is coated with a resist pattern R1 using a photolithography method. 13, form a resist pattern R2 having an outer lead 14, etc. Here, as shown in FIG. The pattern is formed by moving the resist pattern forming device 24 through the resist pattern forming device 24.

Then, as shown in FIG. 3(b), the resist patterns R1 and R2 are used as masks to immerse the etching layer 17.
2L, etching is performed from both sides to form a pattern having a desired shape including thin inner leads 12, dam bars 13, thick outer leads 14, etc. Again, the fourth
As shown in Figure (b), the strip material M on which the resist pattern has been formed is run through the etching device &25 using the unwinding device 21 and the winding device 23, so that etching is performed continuously. It has become.

Then, a polyimide tape 18 for supporting the lead frame is attached to complete the lead frame shown in FIGS. 1(a) and 2 (in FIG. 2, the polyimide tape 18 is
8 has been omitted).

According to this method, etching progresses from both sides of the strip, and the formation of the thin portion and the shape processing are performed simultaneously by etching, thereby making it possible to form a highly accurate pattern with fewer undercuts.

Furthermore, since no press processing is used, there is almost no residual stress and highly accurate pattern formation is possible.

This lead frame is completed as a semiconductor element through processes such as mounting an element chip, wire bonding, and resin sealing, and is extremely reliable.

Furthermore, in the above embodiment, since plating is performed before forming the resist pattern, it is possible to prevent the plating metal from adhering to the entire side of the inner lead, and therefore it is possible to maintain good dimensional accuracy. can. In addition, in areas where silver plating is formed, if plating is performed after pattern formation, the plating metal will adhere to the side of the inner lead, which will not only reduce the 1-pitch level but also generate electromigration silane. By using a method of performing plating before forming a resist pattern, such inconveniences can be prevented and a lead frame with extremely high reliability can be obtained. However, after the etching process for processing the thin portion and shape, plating may be performed on the region corresponding to the tip of the inner lead including the element mounting region.

In the above embodiment, only the inner lead portion is made thin, but other regions such as the outer lead portion may also be made thin.

〔Effect of the invention〕

As explained above, according to the present invention, the formation of the thin wall part and the shape processing are performed simultaneously by etching from both sides, so that the outer frame is thick and strong, while having dimensional accuracy. In areas such as inner lead parts, which have severe conditions, the shape is processed while forming thin parts, so that undercuts are small and it is possible to form highly accurate and reliable fine patterns.

[Brief explanation of drawings]

1 and 2 are diagrams showing a lead frame according to an embodiment of the present invention, FIGS. 3(a) to 3(b) are diagrams showing the manufacturing process of the same lead frame, and FIGS. Figure 4 e
(b) is a diagram showing a lead frame manufacturing apparatus. 11... Die pad, 12... Inner lead, 1
3... Dam bar 14... Outer lead, 15.
16...Side par 17...Support par 18
...Polyimide tape, T...tie bar, M...
Strip material, 21... Unwinding device, 22... Intermittent feeding device, 23... Winding device, 24... Resist pattern forming device, 25... Etching device, R1,
R2...Resist pattern. Figure 3 24 Figure 4

Claims (3)

[Claims] (1) A first resist pattern forming step of selectively forming a resist pattern on the surface of the metal strip, leaving a predetermined area on the surface; and forming patterns such as inner leads and outer leads on the back surface of the metal strip. a second resist pattern forming step of forming a second resist pattern having a second resist pattern; etching simultaneously from the front and back surfaces of the metal strip using the first and second resist patterns as masks to form a thin portion; A method for manufacturing a lead frame, comprising: a double-sided etching step for performing shape processing. (2) The first resist pattern forming step is a step of forming a resist pattern so as to have an opening in a region corresponding to the inner lead and cover the outer lead. A method for manufacturing lead frames. (3) Prior to the formation of the second resist pattern, a plating step is included to form a plating layer on at least the inner lead and outer lead forming regions on the surface of the strip on the side where the second resist pattern is formed. A method for manufacturing a lead frame according to claim (1) or claim (2).