JPS5831293B2 - Molding mold for insert resin sealing - Google Patents

Abstract

PURPOSE:To provided a metal mold with a smooth relief shape subjected to satin finish within a specified range of surface roughness, suitable for molding parts including an insert for resin sealing of semiconductor or the like, which is excellent in the mold releasing property, wear resistance and the like. CONSTITUTION:A metal mold for molding parts including an insert for resin sealing of semiconductors or the like, is subjected to satin finish with the surface roughness ranging from 5 to 15mu with a smooth relief shape by a discharge processing or sandblasting. In addition, the relief shape shall be such that the surface roughness/pitch ranges from 1/10 to 1/200 having the inclination below 10mu/0.2mm within 0-100% of the reference length in the Affot's bearing curve. The performance can be further improved by applying a hard chromium plating or a metal treatment of impregnating a plated metal matrix with a fluorocarbon resin such as tetrafluoroethylene resin or dispersing the resin into the metal matrix.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molding die for molding a component including an insert for resin encapsulation of a semiconductor or the like.

Conventionally, molds for molding parts including inserts for resin encapsulation of semiconductors have generally been mirror-finished.

This is due to the strong need to reduce the force required to release the molded product from the mold, that is, the mold release force.
The mold release force is strong and the adhesive force between the insert and the resin is
Problems such as

However, mirror finishing takes a lot of man-hours, accounting for 10-20% of the mold manufacturing man-hours, and the manufacturing cost is also 10-20% of the total manufacturing cost.
% of the total.

Furthermore, molded products made from mirror-finished molds have the disadvantage that minute sink marks or pinholes are easily noticeable, and the adhesion and durability of markings indicating product names and the like are poor.

These points will be further explained with reference to FIGS. 1 to 5.

FIG. 1 is a cross-sectional view showing an example of a transfer molding mold, and FIG. 2 is a cross-sectional view of a resin-sealed semiconductor manufactured using the mold.

The preformed resin is heated in a high frequency heating machine (not shown).
It is preheated and put into the pot 4, and then the upper mold 1,
It receives heat from the lower mold 2 and melts.

The molten resin 5 is transferred by the plunger 3, passes through the runner 6 and the gate 7, and fills the cavity 8.

The mold is held closed until the resin hardens, and after hardening, the lower mold 2 is moved downward, and the molded product having a shape corresponding to the cavity 8 is released from the upper mold 1 and the lower mold 2.

In the case of a resin-sealed semiconductor, semiconductor pellets 10 are mounted on a lead frame 9 as inserts, and those interconnected with gold wires 11 are placed in a cavity 8 formed by an upper mold 1 and a lower mold 2, and the resin is sealed. It is sealed by 5.

Therefore, if the adhesive force of the resin to the upper mold 1 or the lower mold 2 is strong during the curing process of the resin, internal stress will act due to contraction during curing, and the gap between the semiconductor pellet 10 or lead frame 9, which is the insert, and the resin 5 will be generated. There is a risk that the adhesive may peel off.

If the adhesive force between the resin 5 and the mold is excessive when the lower mold 2 is moved after the curing of the resin 5 is completed, that is, when the mold is released, internal stress will be applied during the mold release, and the strength of the resin will become insufficient. If it is insufficient, cracks may occur in the semiconductor pellet 10.

Such drawbacks are often experienced, and strong adhesion between the mold surface and the resin results in an unreliable product that defeats the original purpose of sealing and protecting the insert with the resin.

Figures 3 to 5 are conceptual cross-sectional views showing the surface shape of the cavity 8. Figure 3 shows a mirror surface, Figure 4 shows a satin surface, and Figure 5 shows a surface formed by grinding or chemical etching. be.

When compared with the surfaces shown in FIGS. 4 and 5, the mirror surface shown in FIG. 3 clearly has a smaller adhesion area with the resin, and it is considered that the adhesive force per apparent unit area is smaller.

In addition, in the case of bonding using an adhesive, etching or sandblasting or the like is usually performed to roughen the surface in order to improve the bonding effect.

It is also generally known that when the cross-sectional shape is as shown in FIG. 5, there is a so-called anchor effect in which the adhesive force increases as the resin enters the small pores on the surface.

For these reasons, it has conventionally been common practice to give the inner surface of the cavity 8 a mirror finish.

The purpose of the present invention is to eliminate the drawbacks of conventional mirror finish molds,
The purpose of the present invention is to provide a mold with excellent mold release properties.

According to the present invention, there is provided a mold for insert resin sealing, which has a smooth uneven shape and has a satin finish with a surface roughness Hmax in the range of 5 to 15 μm.

As for the uneven shape, Hmax/pitch is 1/10 to 1
/200 range, reference length 0 in Abbott load curve
It is desirable that the slope is in the range of 10μ/2007rt7n in the range of 100%, and the satin finish can be conveniently achieved by adjusting the sandblasting conditions or electric discharge machining conditions.

Of course, this finishing process only needs to be performed on the cavity surface.

Furthermore, according to the present invention, the matte finished surface is hard chrome plated or fluorocarbon polymer composite metal surface treatment (processing to impregnate or disperse a synthetic carbon resin such as tetrafluoroethylene resin in the plating metal matrix). A mold for insert resin sealing which has been subjected to metal surface treatments such as the above is also provided.

This further improves mold releasability and abrasion resistance compared to the former.

Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 6 shows an example in which a satin surface was formed on a sample made of 5KD-11 by electrical discharge machining and the surface roughness was actually measured by the stylus method, and FIG. 7 shows its Abbott load curve.

Figure 8 shows the Abbott load curve for the sample in Figure 6 with hard chrome plating with a film thickness of 5 μm, and Figure 9 shows the Abbott load curve for the sample in Figure 6 with hard chrome plating applied to the pear surface with a relatively small surface roughness Hmax. The Abbott load curve is shown.

It can be seen that the Abbott load curves shown in FIGS. 7 to 9 all have a gentle slope in a wide range, and the surface shape is a rough surface that does not include many sharp-edged irregularities.

That is, it has a satin surface shape as schematically shown in FIG. 4, and has no recesses or edges that would have an anchor effect.

It can be seen that by applying the hard chrome plating treatment, the slope becomes gentler and the uneven shape becomes smoother.

Figure 10 shows changes in surface wettability when resin molding is repeated, with chrome plating applied to the mirror surface (A);
Hmax = 5μ and 15μ satin with hard chrome plating (B and C, respectively).

and fluorocarbon polymer composite treatment on a satin finish with lHmax-10μ (D) are shown in comparison.

Wettability is shown as the contact angle of water droplets dropped on the mold surface.

According to Figure 10, (by repeating resin molding, the mold surface is covered with ester, wax, etc. that oozes out from the resin, and this acts as an internal mold release agent, gradually increasing the contact angle and making it difficult to wet. ) It can be seen that with the same surface treatment, a matte surface with a rougher surface is more difficult to get wet, and (1) a fluorocarbon polymer composite treatment is more difficult to get wet than a hard chrome plating treatment.

Figure 11 shows the change in mold release force when continuous molding is performed, for the conventional method with hard chrome plating on a mirror surface (E) and the present invention with hard chrome plating on a matte surface with a surface roughness of 15μ. (F) and a material (G) in which a satin finish with a surface roughness of 10 μm was subjected to a fluorocarbon polymer composite treatment.

Also shown is a mark with hard chrome plating applied to the 111th surface with a surface roughness of 10μ.

It can be seen from FIGS. 11 and 10 that there is a corresponding relationship between wettability and mold release force.

In other words, (7) the fluorocarbon polymer composite treatment, which is the least wettable, has a mold release force of Okg/C711 from the early to late stages of the resin molding process, and (a) the hard chrome plating process has a mold release force of Okg/C711 during the molding process. Initially, the mold release force on the pear-ground surface was stronger than on the mirror surface, but as the surface was gradually covered with mold release agent, the mold release force became smaller than on the mirror surface, and (1) hard chrome plating was applied to the ground surface. Although the wettability of the material is not much different from that of the electrical discharge machined satin surface, the mold release force was measured to be 10 kg/ff1 or more at the initial stage of the molding operation, clearly indicating that an anchor effect exists.

The above data is data obtained by measuring the wettability and mold release force when molding is performed continuously on samples with clean mold surfaces. However, in actual molding work, the mold surface is exposed to mold release agent using dummy shots, etc. It is covered with dirt and is not clean.

Therefore, in the case of hard chrome plating in FIG. 11, it does not actually occur that the matte finish according to the present invention has a greater release force than the mirror finish.

It is clear that fluorocarbon polymer composite metal surface treatment is extremely advantageous.

The relationship between rough surfaces and wettability is generally expressed by Wenzel (W
enzel ).

CO3θ'/cosθ-R θ′: Contact angle on rough surface θ: Contact angle on flat surface R=Ar/Aa (R≧1) AI-: true surface area Aa: Apparent surface area therefore When θ〈90° θ′〈θ When θ〉90° θ′〉θ The relationship holds true.

That is, for a surface material that is easy to wet, the rougher the surface roughness, the easier it is to wet, and for a surface material that is difficult to wet, the rougher the surface roughness, the harder it is to wet.

Therefore, in the case of a mold in which a surface that is difficult to wet is formed using a mold release agent or surface treatment, it has been found that a satin surface is more difficult to wet than a mirror surface and is more advantageous for mold release.

In the case of adhesive processing, the surface is roughened by sandblasting, etc., but this is expected to be effective for surface materials that are easily wetted.

As mentioned above, rough surface roughness is advantageous for mold release, but
Actual molded products have side surfaces, and if the surface roughness is excessive, scratches will occur on the sides when the mold is released.

The satin finished surface according to the present invention has good mold releasability, so it peels off from the mold surface during curing and shrinkage, but in order to prevent galling, it is necessary to make the draft angle excessively high, and HmaX is 15
It is desirable that it be less than μ.

However, if Hmax is made smaller than 5μ, the difference from the mirror finish becomes small, and the effects of the present invention cannot be obtained.

Round bars made of 545C material with various surface roughnesses were embedded and molded in resin without a release agent, and the pulling force was measured. As a result, the maximum value of the pulling force FmaX was FmaX = 1131og
R+327 However, the diameter of the round bar is 10mm, R-) (given as max).

) It has been found that when Imax becomes larger than 15μ, pmax becomes significantly large.

When R=0.4μ, Fmax=270−, R=
When 20μ, FmaX becomes 1500)ci9.

The uneven shape must be smooth, and Hmax
/If the pitch is larger than 1/10, that is, if Hmax is too small for the pitch, scratches will occur on the molded product unless the side wall slope is made thicker.

In the case of a molded article with a normal draft angle (approximately 95°), it is desirable that this value be smaller than 1/10.

Furthermore, if this value is greater than 1/10, an anchor effect will occur.

Note that it is difficult to form by sandblasting or electric discharge machining when the r11ax/pitch is smaller than 1/200.

Another indicator for determining the shape of unevenness is the Abbott load curve.

This indicates how uniform the shapes of the recesses (pits) are in the measurement range (reference length), and preferably the slope is 10μ70.2 in the range of 0 to 100% of the reference length.
It shall be less than mm.

In particular, the slope in the range of 0 to 5% of the reference length is 10μ10
．． If it exceeds 2 mm, it indicates that the tip of the convex portion is sharp as in the case of a sandpaper polished surface, and an anchor effect will occur.

When applying markings to display product names etc. on molded products,
Marking is performed after the molded product has been cleaned to remove mold release agents and other substances from the surface.

At this time, the surface is easily wetted, and the adhesion of marking ink to a molded product molded with a satin finish mold is superior to that of a molded product molded with a mirror finish mold.

The appearance of the molded product molded using the matte-finished mold is extremely good.

This is because, as mentioned above, the satin surface is difficult to wet and therefore difficult to bond with the resin, so the stress caused by the curing and shrinkage of the resin is not transmitted to the surface of the mold, and uniform adhesive peeling tends to occur, resulting in local sink marks. This is thought to be because it is difficult.

This is also advantageous for adhesion with resin inserts.

Since the molded product according to the present invention does not reflect light like a mirror-finished molded product, minute sink marks or pinholes are less noticeable, giving the product an image of being a high-quality product.

According to the present invention, the following effects can be obtained by changing a conventional mirror-finished mold to a matte finish.

(Power) A satin finished surface that does not have a shape where the resin wedges into the concave part of the satin finish can be easily formed by electric discharge machining, sandblasting, etc., so the man-hours required for conventional mirror finishing processing can be omitted, and the mold Production time: 10-2
It is possible to reduce the time by 0% and reduce the manufacturing cost by about 10 to 20%.

(a) The satin surface finish improves mold releasability and reduces the number of dummy shots by approximately 30 compared to conventional molds.
% can be reduced.

(1) Since the mold releasability is improved, the adhesion between the insert and the resin is significantly improved, the defect rate of the product is reduced, and the moisture resistance reliability is improved.

E) Minute defects such as sink marks and pinholes become less noticeable, giving the product a high-class image and increasing its value.

(1) The adhesion and durability of the marking ink were improved, and the number of marking defects was reduced to about 175.

) By applying a satin finish surface treated with a fluorocarbon polymer composite metal surface to a mold for forming a thin-walled small package, mold release properties are greatly improved, and the incidence of mold cracks is lower when compared under the same molding conditions. It is possible to reduce the pellet crack occurrence rate to about 1,710, which is about 1/100.

Comparing the molding conditions, even if the curing time of the resin is halved, the defect rate can be reduced to the same level as in the case of a mirror-finished mold, which is highly effective in shortening the molding cycle.

That is, the cycle time can be reduced by about 40% within the current defect limit, and production efficiency can be greatly improved.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a transfer mold type for explaining an example of resin sealing including an insert, Fig. 2 is a cross-sectional view of a resin-sealed IC shown as an example of an insert resin-sealed product, Fig. 3, Figures 4 and 5 show mirror surface, pear surface, and
A schematic cross-sectional view of a rough surface having an anchor effect, FIG. 6 is a graph showing roughness measurement data of a matte surface formed by electric discharge machining according to the present invention, FIG. 7 is an Abbott load curve diagram thereof, and FIG.
The figure shows the Abbott load curve when the pear-shaped surface shown in Fig. 6 is plated with hard chrome, and Fig. 9 shows the Abbott load curve when the pear-skinned surface shown in Fig. 6 is plated with hard chrome. Fig. 10 is an Abbott load curve diagram of the object, which shows the change in wettability of the mold surface when resin is continuously molded into the mold according to the present invention, comparing it with a conventional mirror-finished mold. The figure shown in FIG. 11 is a diagram showing the mold release force between the mold and the resin according to the present invention in comparison with the case of conventional mirror finishing and the case of grinding. 1...Top mold, 2...Bottom mold, 3...
...Plunger, 5...Resin, 8...
cavity.

Claims (1)

[Claims] 1. A mold for insert resin sealing, characterized in that the cavity surface thereof has a smooth uneven shape and has a satin finish with a surface roughness Hmax in the range of 5 to 15μ. . 2 The uneven shape has a Hmax/pitch of 1/10 to
The insert resin seal according to claim 1, wherein the slope is limited to 10μ/0.2 mm or less in the range of 1/200% and the reference length in the range of 0 to 100% in the Abbott load curve. Molding mold for stopping. 3. The insert resin sealing mold according to claim 1 or 2, wherein the satin surface finish is formed by electric discharge machining or sand blasting. 4 Hard chrome plating on the pristine surface whose cavity surface has a smooth uneven shape and a surface roughness Hmax in the range of 5 to 15μ, or impregnation of a synthetic carbon resin such as tetrafluoroethylene resin in the plating metal matrix. Alternatively, a mold for insert resin sealing characterized by being subjected to a dispersive metal surface treatment. 5 The uneven shape has a Hmax/pitch of 1/10 to
The insert according to claim 4, characterized in that the slope is limited to 10 μ/0.2 mm or less in the range of 1/200 and in the range of 0 to 100% of the reference length in the Abbott load curve. Molding mold for resin sealing. 6. Claim 4, wherein the satin surface is formed by electric discharge machining or sandblasting.
The mold for insert resin sealing according to item 1 or item 5.