JPH0142503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a method for manufacturing a lead frame used for semiconductor devices, etc., and particularly relates to a method for manufacturing a lead frame in which a desired portion is coated with an Al or Al alloy film. It is something.

(2) Background of the technology Metal strips are manufactured with Al or Al alloy coatings (hereinafter referred to as Al coatings) partially deposited on one main surface of the metal strips at precise positions, and then press-formed. There is a need for a means for efficiently manufacturing a lead frame that does not cause misalignment of the Al coating at the desired position of the lead frame after press working.

(3) Conventional technology and problems Conventionally, metal strips were used to partially apply Al to desired areas.
As a manufacturing method for continuously pressing a lead frame coated with a coating, a method is used in which an Al coating is applied to one main surface of a metal strip, and then press processing is performed continuously. ing. An example of a lead frame manufactured by this method is shown in the first example.
Shown in Figure a. In the figure, 1 is a frame part, 2 is an internal lead, 3 is an external lead, 4 is an Al coating area,
5 indicates a package area.

According to this method, the internal leads 2 that require Al coating are formed into continuous strips between unit lead frames.
By applying the Al coating, the entire Al coating area 4 will contain the Al coating. Therefore, by continuously press working using a metal strip in which the Al coating is applied to the Al coating area 4 in the form of a band, the Al coating can be applied to the desired area. A lead frame with a coating applied is manufactured. In this case, since the Al coating region 4 is included in the package region 5 of the semiconductor device, the problem of corrosion of the Al coating exposed outside the package region does not occur.

However, if a metal strip similar to that used in processing the lead frame shown in Fig. 1a is used, the lead frame shown in Fig. 1b is
Or, if a lead frame with a desired Al coating area 4 as shown in c is pressed, the desired Al coating area 4 can be formed.
In addition to the Al coating area 4, for example, a part of the external lead 3 exposed from the package area 5 is also coated with Al coating continuously with the internal lead 2, resulting in a lead frame. In this state, the semiconductor chip is mounted on the lead frame coated with Al coating, the semiconductor chip and the internal leads are connected using thin metal wires such as aluminum, and the package area is sealed with synthetic resin, low melting point glass, etc. In a hermetically sealed semiconductor device, the Al coating is exposed outside the package area in a continuous manner with the internal leads, and corrosion of the exposed Al coating progresses to the inside of the package area, reducing the lifespan of the semiconductor device. There are drawbacks that may cause damage and reduce high reliability. Therefore, Fig. 1 b or c
When manufacturing a lead frame as shown in Figure 1 using a metal strip covered with an Al coating, it is necessary to remove the Al coating from the portion exposed from the package area before pressing.

Normally, the Al coating on unnecessary areas is removed by chemical etching, etc., but the method is to attach a covering tape to the Al coating on the desired area to protect it from corrosion by the etching solution, and then affix the covering tape. The covering tape is peeled off after the Al coating is removed by corrosion.

In order to attach the coating tape to the metal strip, it is possible to punch out the coating tape in the shape of the Al coating on the desired part of each unit lead frame using a press die and apply it. Pressing is difficult and workability is poor unless the covering tape affixed to the surface is peeled off individually.

In addition, a continuous coating tape with holes punched out is pasted on the part where the Al coating is to be removed, and the unnecessary part is removed.
Another option is to remove the Al coating by corrosion, but in this case, since the coating tape is continuous, it is possible to hold one end and peel it off continuously, but since it is in a continuous state when pasting, the coating tape It tends to expand and contract, making it difficult to paste in the correct position.
A positional shift occurs between the position of the Al coating and the desired position of the Al coating after processing the lead frame. In addition, with this method, if the Al coating of the metal strip is applied to the entire surface of one main surface, the Al coating cannot be corroded away from the areas where the coating tape is attached other than the punched holes, leaving unnecessary Al coating that cannot be peeled off. Therefore, it is necessary to use a metal strip coated with a strip-shaped Al coating that is narrower than the width of the punched hole in the covering tape.

In this way, in the conventional method using a covering tape, the position of the desired Al covering after the lead frame is press-formed is misaligned with the desired part of the Al covering that is left without corroding away the Al covering after applying the covering tape. Accurately place Al on the desired part of the lead frame
Applying the coating is extremely difficult. Even if the Al-coated position of the metal strip and the desired Al-coated part are precisely matched during press processing, it is extremely difficult to perfect the feed accuracy of the press, and feed errors accumulate and the position shifts as the process progresses. occurs. In addition, conventional coated tapes are applied to the surface of the Al coated surface.
The adhesive of the covering tape tends to remain when it is peeled off, and if it is attached, a treatment is required to remove it.

It is also possible to attach a covering tape after pressing the lead frame and remove the Al coating from unnecessary parts, but the shape of the lead frame is easily deformed during handling, and depending on the shape of the lead frame, it is difficult to apply the covering tape. It is difficult and therefore impractical.

In this way, the conventional method using covered tape
There is a drawback that the Al coating cannot be applied to the exact position of the lead frame because the position of the Al coating does not match the desired position of the Al coating after press working, resulting in a positional shift. Therefore, when manufacturing a lead frame as shown in Figure 1 b or c, a metal strip is pressed before being coated with Al coating to form a continuous lead frame, and then multiple unit lead frames are connected. A lead frame cut into a sheet or formed by etching from a metal plate is mounted on a vapor deposition jig that covers parts that do not require Al coating with a metal mask, etc., and then partially coated using a vacuum process such as vacuum vapor deposition. A method of depositing an Al coating is generally used. However, although this method allows for accurate placement of the Al coating, unlike the case of metal strips, it cannot be processed continuously.
Since the amount of processing per cycle is limited, productivity is poor and it is unsuitable for mass production, resulting in high costs. In addition, the work of attaching and removing the lead frame to and from a vapor deposition jig equipped with a metal mask, etc., requires manual labor, resulting in poor work efficiency and the disadvantage that the lead frame is easily deformed when handled. .

(4) Purpose of the Invention Therefore, the present invention was proposed to eliminate the above-mentioned drawbacks, and it is possible to manufacture a metal strip partially coated with Al coating at a precise position for each unit lead frame. It is an object of the present invention to provide a method for manufacturing a lead frame that does not cause displacement of the Al coating position even when the frame is continuously pressed and has good productivity.

(5) Structure of the invention The purpose of this invention is to apply a heat-peelable adhesive sheet to a metal strip coated with an Al coating on one main surface using positioning means provided regularly as a reference, and then apply the heat-releasable adhesive sheet to the metal strip. This is achieved by removing the Al coating other than the part to which the releasable adhesive sheet is attached, then heating and peeling off the heat releasable adhesive sheet, and pressing using the positioning means as a reference.

(6) Embodiments of the invention Examples of the invention will be described below in detail with reference to the drawings.

FIGS. 1b and 1c show an example of a lead frame manufactured by the manufacturing method of the present invention.

First, the thickness is 0.25 [mm] and the width is made of iron-nickel alloy.
4 [μm] of Al coating is deposited on the entire main surface of the 33 [mm] metal strip by vacuum evaporation, and reference holes with a diameter of 1.5 [mm] are press-formed at regular intervals on the metal strip. Continuously punch out. A front view of the metal strip in this state is shown in FIG. 2a, and a sectional view thereof is shown in FIG. 2b. In the figure, 21 is a metal strip, 22 is an Al coating, and 23 is a reference hole. In this example, the reference hole 2
The pitch of No. 3 was made the same as the pitch of the unit lead frame, and two reference holes were punched out per unit lead frame.

Next, using this reference hole 23 as a reference, a heat-peelable adhesive sheet is partially attached to a desired Al-coated portion of the Al-coated portion of the Al-coated portion 22 coated on one main surface of the metal strip when the lead frame is completed. This is an unnecessary part
This is to protect the Al coating from corrosion in the necessary areas when removing the Al coating from corrosion. A front view of this state is shown in Fig. 2c, and a cross-sectional view is shown in Fig. 2d. In the same figure, 24
is the heat-peelable adhesive sheet, and the other parts are the second
The same parts as in figures a and b are given the same reference numerals. This heat-peelable adhesive sheet (hereinafter referred to as adhesive sheet) is an adhesive that has adhesive strength to the adherend that is smaller than the thermal deformation stress of the support, and is made by laminating two or more layers with different thermal expansion and contraction rates. In this example, the adhesive surface of the adherend, that is, the Al-coated part of the metal strip, is a polyurethane adhesive layer with a thickness of 20 [μm], and the support is a calcium carbonate 30 μm layer in contact with the adhesive layer.
An adhesive sheet is used in which a polyethylene layer with a thickness of 20 [μm] is laminated on a polypropylene layer with a thickness of 40 [μm] containing % by weight.

Such an adhesive sheet is partially pasted on the part of the metal strip to be coated with Al at room temperature or in a heated state.
Afterwards, it peels off in a very short time by heating it to a higher temperature than when it was pasted, but since this is a laminate made of two or more layers with different thermal expansion and contraction rates, it curls and peels off due to the difference in thermal expansion and contraction rates. Since the adhesive force of the adhesive layer to the metal strip is smaller than the thermal deformation stress of the laminate, no adhesive remains on the Al-coated surface of the metal strip.

The adhesive sheet that can be used in the manufacturing method of the present invention can be a laminate made of a combination of various materials, which was proposed in Japanese Patent Application No. 56-196969.

After this adhesive sheet is partially attached to the desired portion of the metal strip to be coated with Al, the portion where the adhesive sheet is not attached, that is, the portion where Al coating is unnecessary is etched away by chemical etching. The etching solution is approximately
Sodium hydroxide (NaOH) heated to 60 [℃]
This is done by using a 10% solution and immersing a metal strip with an adhesive sheet attached in this solution. At this time
The removal rate of the Al coating is about 4 [μm] per minute. The etching solution is 20% hydrochloric acid (HCl).
Use a processing solution that can etch the Al coating, such as a solution.

A cross-sectional view of the state in which unnecessary portions of the Al coating have been removed in this manner is shown in FIG. 2e. Next, the adhesive sheet 20 is heated by blowing hot air at about 120 to 200 degrees Celsius onto the metal strip in this state.
curls and peels off. If the adhesive sheet is heated with the pasting surface facing downward, it can be easily peeled off by the adhesive sheet's own weight or by blowing hot air. In this way, unlike conventional coated tapes, it can be peeled off very easily by heating, which simplifies the peeling operation and improves workability. A cross-sectional view after peeling off the adhesive sheet is shown in FIG. 2f.

In this way, a metal strip is obtained with the Al coating deposited at the exact desired location. By continuously press-working the metal strip in this state using the first-formed reference hole as a reference, a lead frame as shown in FIGS. 1b or 1c, for example, is completed.

FIG. 3 schematically shows an apparatus for pasting an adhesive sheet onto a metal strip. In the figure, 31 is a punch, 32 is an air suction hole, 33 is a punching die, 34 is an adhesive sheet feed guide, 35 is a pilot pin, 36 and 36' are heaters, and 37 is a pressure roller. The same parts as in FIG. 2 are given the same reference numerals as in the same figure.

The Al coating 22 is applied to the entire surface of one main surface, the reference hole 23 is formed by press working, the metal strip is intermittently moved, the adhesive sheet is also intermittently fed in conjunction with this, and the punch 31 is used to Along with punching
At this time, the pilot pin 35 is inserted into the reference hole 23 to confirm whether the position of the metal strip is correct, and at the same time the punch 31 is lowered to punch out the adhesive sheet 24 into the desired shape. Attach the adhesive sheet to the desired area to be coated with Al. At this time, the pilot pin 35 is inserted into the reference hole 2.
When the punch is not inserted into the hole 3, the punch is configured to operate in conjunction with the punch so that it does not fall. The punch for punching the adhesive sheet 24 has an air suction hole 32 inside and punches the adhesive sheet 24 fed by the adhesive sheet feeding guide 34 between the punch die 33 and the punch 3.
After punching into a desired shape according to step 1, the punch punch holds the adhesive sheet by suction through the air suction holes, and releases the suction force at the same time as the pasting is completed.

In this way, the adhesive sheet is pasted on the desired portion of the metal strip to be coated with Al by repeating the adhesive sheet pasting operation. The temperature at which this adhesive sheet is applied is determined by heating the metal strip to approximately 80[° C.] using a heater 36 built into the lower part of the punching device. It is desirable that the metal strip partially coated with the adhesive sheet is further passed between a heater 36' heated to about 80 degrees Celsius and a pressure roller 37 to be pressed and bonded sufficiently.

When the adhesive sheet pasted in this manner is to be peeled off after etching, it can be peeled off by heating it to about 120 to 200 [°C] with a heater 41 as shown in Figure 4. By blowing hot air, it can be removed quickly and reliably.

Above, we have described an example of a method for manufacturing a lead frame in which a desired portion is coated with Al using an adhesive sheet, but these manufacturing steps can be performed in the form of a metal strip, and All feeding and winding can be done continuously using a reel.

The material of the metal strip is iron-nickel-cobalt alloy.
Any metal can be used as long as it can be used as a lead frame, such as copper or copper alloy.

In this example, a case was explained in which a metal strip with Al coating applied to the entire main surface was used. A metal strip or the like may also be used. In addition, a positioning means was provided for each unit lead frame to align the position of the Al coating with the position of the desired Al coated part after press working, but regular positioning means such as round holes, square holes, notches, etc. , position, and quantity may be arbitrary. Regarding the processing of the positioning means, a new positioning means is separately processed based on the first processed positioning means and used as a positioning means during press processing, or a positioning means is provided in a part that is punched out and becomes an unnecessary part during lead frame processing. Alternatively, a part of the shape of the lead frame may be punched out in advance and used as means for positioning the punched hole. Note that the adhesive sheet can be attached simultaneously to a plurality of unit lead frames using a plurality of punches, or to a plurality of metal strips at the same time.

(7) Effects of the Invention According to the present invention, when manufacturing a lead frame in which a desired portion of a unit lead frame is coated with an independent pattern of Al coating, the adhesive sheet is placed in an accurate position based on the positioning means provided on the metal strip. Paste the
Furthermore, since the lead frame is pressed using this positioning means as a reference, there is no possibility of misalignment of the Al coating, and the adhesive sheet can be peeled off extremely easily by heating, which has the effect of improving productivity. .

[Brief explanation of drawings]

FIG. 1 shows an example of a lead frame press-formed using a metal strip coated with a conventional Al coating in the form of a band, and FIGS. 1B and 1C show examples of lead frames press-formed by the method of the present invention. Fig. 2 is a plan view and a sectional view showing the manufacturing process of the present invention, Fig. 3 is a schematic diagram showing an embodiment of an adhesive sheet pasting device, and Fig. 4 is a sectional view showing an embodiment of an adhesive sheet peeling method. It is. In the figure, 1... Frame part, 2... Internal lead, 3... External lead, 4... Al covering area,
5...Package area, 21...Metal strip, 22
... Al coating, 23 ... Reference hole, 24 ... Adhesive sheet, 31 ... Punch punch, 32 ... Air suction hole, 33 ... Punching die, 34 ... Adhesive sheet feeding guide, 35 ... Pilot pin, 36,3
6', 41... Heater, 37... Pressure roller, 4
2...Hot wind.

Claims (1)

[Claims] 1 A heat-peelable adhesive sheet is attached to a metal strip having an Al or Al alloy film coated on one main surface, using positioning means provided regularly as a reference, and then the heat-peelable adhesive sheet is attached. A method for producing a lead frame, comprising removing the Al or Al alloy film other than the portion, heating and peeling off the heat-peelable adhesive sheet, and pressing using the positioning means as a reference.