JPH07273265A - Method for manufacturing lead frame with resin dam bar - Google Patents

Abstract

PURPOSE:To eliminate resin leakage when forming a mold by prescribing drying and forming conditions after applying resin. CONSTITUTION:A thermoplastic insulation resin 4 in varnish shape after being melded in a solvent medium is applied to leads 2. After the coating, a lead frame 1 is heated closer to glass transformation temperature and is dried until the amount of remaining solvent medium contained in the thermoplastic insulation resin 4 is equal to or less than 5%. After that, both sides of the application site of the thermopllastic insulation resin 4 is held by hot plates 6, 6 by including heat resistance macromolecular films 5, 5. The hot plates 6, 6 are heated to a temperature exceeding the glass transformation temperature of the thermoplastic insulation resin 4. When the application site of the thermoplastic insulation resin 4 is pressurized by the heated hot plate 6, the area between the leads 2 is completely filled with the thermoplastic insulation resin 4, thus completing a dam bar.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a lead frame with a resin dam bar, in which a dam bar made of an insulating resin is formed between the leads so that the dam bar does not have to be removed after molding, and more particularly to an outer lead. The present invention relates to a multi-pin lead frame having an extremely narrow pitch, which prevents resin leakage during molding.

[0002]

2. Description of the Related Art In conventional lead frames, the spaces between the leads are integrally formed by metal dam bars made of the same material as the leads. Therefore, after molding, the dam bars must be cut with a dedicated punching die. As the number of pins increases and the distance between leads becomes narrower, it becomes difficult to cut the dam bar. For example, the external dimensions of the semiconductor device are 28
If the number of pins is mm x 28 mm and the number of pins is 208, the outer lead spacing will be 0.3 mm or less.
The outer lead spacing is 0.2 mm or less when there are 44 wires. Punches with such very close spacing are very fragile and time consuming and expensive to manufacture and maintain.

Therefore, in order to omit the dam bar cutting, a structure in which the dam bar is made of an insulating resin has been proposed.
In this method, a varnish-like insulating resin is applied to the leads and then dried to replace the metal dam bar.

[0004]

However, in the conventional method of providing the insulating resin instead of the metal dam bar, the insulating resin is applied to the upper and lower surfaces of the leads only by applying the insulating resin and then drying it to form the dam bar. Remaining, the thickness of the lead is apparently increased. Further, a large amount of solvent is contained in the varnish-like insulating resin, and the thickness of the resin between the leads becomes too thinner than the thickness of the leads due to evaporation by drying after coating. If the step between the insulating resin on the leads and the insulating resin between the leads is emphasized in this way, the possibility of resin leakage during molding becomes extremely high. It was a big problem for the frame.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a method of manufacturing a lead frame with a resin dam bar in which resin does not leak during molding.

[0006]

A method of manufacturing a lead frame with a resin dam bar according to the present invention includes a step of applying a thermoplastic varnish-like thermoplastic insulating resin dissolved in a solvent to the leads to provide a dam bar between the leads. After applying the thermoplastic insulating resin that becomes the dam bar to the leads, evaporate the residual solvent amount in the thermoplastic insulating resin to 5% or less, and then, the portion where the thermoplastic insulating resin is applied is changed to the glass transition temperature. By pressing at the above temperature, the thermoplastic insulating resin is pushed between the leads.

The dam bar made of a thermoplastic insulating resin is mainly provided in the outer lead portion and is used for preventing resin leakage during molding of the semiconductor device or fixing the lead. A dispenser is used as a means for applying the thermoplastic insulating resin to the leads in order to form the dam bar. Polyether amide imide is suitable for the thermoplastic insulating resin, and N-methyl-2 is used as a solvent for forming the thermoplastic insulating resin into a varnish.
-Pyrrolidone and butyl cellosolve acetate are suitable.

[0008]

First, the leads are coated with a varnished thermoplastic insulating resin dissolved in a solvent. The use of the thermoplastic insulating resin eliminates the need for curing to accelerate curing unlike the thermosetting resin, and facilitates shaping at the glass transition temperature. After application, the lead frame is heated to near the glass transition temperature and dried until the amount of residual solvent contained in the thermoplastic insulating resin is 5% or less. Then, since the apparent thickness of the insulating resin is substantially eliminated, the resin between the leads will not become thinner than the thickness of the leads even after heating. If it exceeds 5%, the apparent lead thickness cannot be ignored and resin leakage cannot be prevented. In order to determine that the residual solvent amount in the thermoplastic insulating resin is 5% or less, the difference in weight including the lead frame before and after drying is determined.

Next, the portions where the thermoplastic insulating resin is applied are sandwiched by hot plates from both sides. At this time,
It is preferable to sandwich it between a thermoplastic insulating resin and a heat-resistant polymer film that is easily peeled off, and apply pressure from both sides. If you sandwich the application site with a heat resistant polymer film,
The insulating resin moves smoothly between the leads, and the applied pressure is also softly applied to the leads, so that the leads are not deformed during resin shaping.

The temperature of the hot plate is set to a temperature higher than the glass transition temperature of the thermoplastic insulating resin. In order to smoothly push the thermoplastic insulating resin between the leads, it is advisable to impart fluidity to the thermoplastic insulating resin at a temperature equal to or higher than the glass transition temperature and pressurize this.

When a heated hot plate is applied to a portion to which the thermoplastic insulating resin is applied, excess thermoplastic insulating resin on the lead surface flows between the leads and fills the gaps without gaps, so that a stepless dam bar is formed. Complete. This effectively prevents resin leakage during molding.

[0012]

EXAMPLE An example of a method for manufacturing a lead frame with a resin dam bar according to the present invention will be described below with reference to FIGS. Although a lead frame having a small number of pins is illustrated in FIG. 2 for convenience, it may be regarded as a multi-pin lead frame.

First, the thermoplastic insulating resin is dissolved in a solvent in advance to form a varnish. This is put in the dispenser 3 and the thermoplastic insulating resin 4 is placed over the leads 2 so as to straddle the leads.
It is applied linearly on the surface (Fig. 2). The coating may be applied to both sides of the lead 2. As a coating method, the lead frame 1 may be moved, the dispenser 3 may be moved, or both may be moved. When it is linearly applied in a direction intersecting with the leads 2, a dambar master made of the thermoplastic insulating resin 4 is formed between the leads 2.

After the application of the thermoplastic insulating resin 4 to the leads 2, the lead frame 1 is left on the hot plate 6 heated to a temperature near the glass transition temperature for a predetermined time, and the amount of the residual solvent contained in the thermoplastic insulating resin is increased. To 5% or less (Fig. 3). The determination of 5% or less may be performed in real time, or may be taken out from the hot plate after standing and measured.

After that, the portion coated with the thermoplastic insulating resin 4 is sandwiched between the hot plates 6, 6 from both sides (FIG. 1). At this time, it is advisable to sandwich the part between the thermoplastic insulating resin 4 and the heat-resistant polymer films 5 and 5 which are easily peeled off.
The heat-resistant polymer film 5 is a polyimide film, and its thickness is preferably about the thickness of the lead 2 at the application site or thinner than the lead 2 in terms of heat resistance, releasability, and flatness. .

The temperature of the hot plates 6 sandwiched from both sides is set to a temperature higher than the glass transition temperature of the thermoplastic insulating resin 4. When the area coated with the thermoplastic insulating resin 4 is pressed between the hot plates 6 and 6 heated to this temperature, the fluidized thermoplastic insulating resin 4 flows between the leads 2 and the thermoplastic insulating resin 4 between the leads 2. It is filled with no gaps and the dam bar is completed (Fig. 4). This effectively prevents resin leakage during molding.

(Embodiment 1) In this embodiment, the lead frame is 42 alloy, the lead thickness is 0.15 mm, the outer lead pitch is 0.5 mm, the outer lead width is 0.2 mm, the outer lead interval is 0.3 mm, and the number of pins is 208. A semiconductor device of a QFP (Quad Flat Package) type having an outer dimension of 28 × 28 was used.

The insulating resin 4 was in the form of varnish, and HM-1 (trade name) manufactured by Hitachi Chemical Co., Ltd., which is a thermoplastic polyether amide imide having a glass transition temperature of 230 ° C., was used.
This was applied while moving on the lead with a dispenser. After application, the solvent in the thermoplastic insulating resin is evaporated by leaving it on the hot plate for a predetermined time. However, as shown in Table 1, the drying conditions such as the hot plate temperature or the standing time may be changed. The amount of solvent was changed.

Next, the thermoplastic insulating resin 4 and the heat-resistant polymer film 5 which is easily peeled off, here a polyimide-based film having a thickness of 0.1 mm, sandwiches the insulating resin 4 application portion of the lead frame 1, and further A dam bar was formed by embedding the insulating resin 4 between the leads by heating and applying pressure from both sides of the hot plate 6 at 250 ° C., which exceeds the glass transition temperature of the insulating resin. The pressing force is large enough to push the excess resin on the surface of the leads between the leads and not to deform the leads, for example, about 50 N per lead.

Thereafter, a semiconductor element was mounted on this lead frame (pellet attachment), wire bonding was performed between the semiconductor element and the inner lead, and then resin molding was performed to form a package. Table 1 shows the results of the examination of the leakage of the mold resin at that time. The table result is measured at 208 points.

[0021]

[Table 1]

If the amount of residual solvent exceeds 5%, leakage of the molding resin occurs during molding. This is because the residual solvent in the resin embedded between the leads evaporates due to heating during pelleting and wire bonding,
It is considered that the mold resin leaked because the volume of the resin decreased and a gap was created in the resin between the leads. From this result, the amount of residual solvent in the thermoplastic insulating resin must be 5% or less.

Example 2 A varnish-like thermoplastic insulating resin was applied and dried under the same conditions as in Example 1 to make the residual solvent amount in the resin 3%. The lead frame with a resin dam bar was heated and pressed at the temperatures shown in Table 2 to embed a resin between the leads. The glass transition temperature of this resin is 230 ° C. as described above.

Thereafter, pelleting and wire bonding were carried out for resin molding, and the leakage of the molding resin at that time was examined. The results are shown in Table 2. The table results are measured at 208 points, as in Table 1.

[0025]

[Table 2]

When heating and pressurizing at a temperature below the glass transition temperature (230 ° C.), leakage occurred. This is because below the glass transition temperature, the resin flow is not sufficient, so that the space between the leads cannot be filled with the resin, and a gap is formed between the leads, and the mold resin leaks from the gap. From this result, the temperature at which the resin is heated and pressed should be higher than the glass transition temperature.

(Example 3) The present invention was applied to a lead frame used in the same way as in Example 1 except that the number of pins was 344 and the outer lead interval was 0.2 mm or less, but the same as in Examples 1 and 2. Results were obtained.

[0028]

EFFECTS OF THE INVENTION According to the present invention, after the residual solvent amount is evaporated to 5% or less, the thermoplastic insulating resin at the application site is pressed at the glass transition temperature or higher, so that there is no resin leakage during molding. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram at the time of heating and pressurizing a resin for explaining an embodiment of a method for manufacturing a lead frame with a resin dam bar according to the present invention.

FIG. 2 is an external view of a lead frame when a resin is applied according to this embodiment.

FIG. 3 is a cross-sectional view of a dam bar portion after resin drying according to this embodiment.

FIG. 4 is a sectional view of the dam bar portion after resin heating and pressurization according to the present embodiment.

[Explanation of symbols]

 1 lead frame 2 lead 3 dispenser 4 thermoplastic insulating resin 5 heat resistant polymer film 6 hot plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuya Otaka 3550 Kidayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable Ltd. System Materials Laboratory (72) Inventor Yasuharu Kameyama 3550 Kidayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable (72) Inventor Hideyuki Koyama, 3550 Kidayo-cho, Tsuchiura-shi, Ibaraki Hitachi Cable, Ltd.

Claims (3)

[Claims] 1. A varnish-like thermoplastic insulating resin dissolved in a solvent is applied to the leads to form dam bars between the leads. After applying the thermoplastic insulating resin to be the dam bars to the leads, By evaporating the amount of residual solvent in the thermoplastic insulating resin to 5% or less, and then pressing the portion coated with the thermoplastic insulating resin at a temperature equal to or higher than the glass transition temperature of the thermoplastic insulating resin, A method of manufacturing a lead frame with a resin dam bar, characterized in that a thermoplastic insulating resin is pushed between the leads. 2. When pressurizing a portion coated with the thermoplastic insulating resin, the portion is sandwiched between the thermoplastic insulating resin and a heat-resistant polymer film that is easily peeled off, and pressure is applied from both sides thereof. The method for manufacturing a lead frame for a semiconductor device according to claim 1. 3. The method for producing a lead frame with a resin dam bar according to claim 1, wherein the thermoplastic insulating resin is polyether amide imide.