JP2576018B2 - Resin tablet for semiconductor encapsulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin tablet for encapsulating a semiconductor used for encapsulating a semiconductor by a runnerless method (also referred to as a multi-plunger method) which is a kind of transfer molding.

[0002]

2. Description of the Related Art In a conventional transfer molding for sealing a semiconductor with a resin, a pot provided with a plunger, a large number of runners radiating from the pot, and each runner are communicated via a gate. Using a molding die having a large number of cavities, one semiconductor element assembly is placed in each cavity of the die, and a resin tablet is put into the above pot, and this is heated by the die heat. A method is employed in which the material is pressurized by a plunger while being melted, and is melt-pressed into each cavity via the runner and the gate.

However, in this molding method, since the resin put into the pot remains on the pot and each gate, as well as on a runner having a long and wide cross-sectional area, the resin loss after molding becomes extremely large. There is.

On the other hand, in recent years, as a runnerless transfer molding, a plurality of pots having a plunger are provided, and the sealing resin put into each pot is directly gated without passing through a runner. An attempt has been made to perform resin sealing of a semiconductor by using a molding die of a method of melting and press-fitting into each cavity through a mold (see FIG. 1). This molding method has an advantage that the material cost can be significantly reduced because there is no resin loss caused by the above-mentioned conventional runner.

However, in such a runnerless molding method, air bubbles (hereinafter, referred to as voids) are apt to be generated inside the sealing resin, which causes a decrease in the moisture resistance reliability of the semiconductor device and a decrease in mechanical strength. It is a cause of the decline.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the runnerless transfer molding which is much more advantageous in terms of material cost as described above, and reduces voids inside the sealing resin. It is an object of the present invention to obtain a semiconductor device having excellent moisture resistance reliability.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the above object, and as a result, in the runnerless transfer molding, the melt viscosity of the resin tablet used in the transfer molding has been reduced by the bonding wire in the semiconductor element assembly. When the melt viscosity is set to a specific range and the tableting density of the tablet is set to a specific range, the voids are significantly affected. The present inventors have found that a highly reliable semiconductor device having a small number of defects and no occurrence of defective products as described above can be obtained, and the present invention has been completed.

That is, the present invention provides a pot having a pot and one end directly connected to the pot and the other end directly connected to a cavity in which a semiconductor element assembly is arranged. A thermosetting resin in a semiconductor encapsulating resin tablet which is injected into the cavity and melt-pressed into the cavity via the gate.
Resin as a curing agent and Novolats as a curing agent
And a melt viscosity at a mold temperature for the above-mentioned melt injection in the range of 500 to 1,000 poise, and a tableting density. Is 90% or more.

In this specification, the melt viscosity of the resin tablet is defined as the composition of 2 g of the tablet being molded into a size (tablet) having a cross-sectional diameter of 10 mm and a height of 15 mm, and using this molding material for Shimadzu. Koka type flow
Tester (nozzle diameter 1mm, nozzle length 10mm, load 10
Kg / cm ² ) at a predetermined temperature (mold temperature).

The above-mentioned tableting density means a molding density at the time of compression molding at room temperature from a composition containing a thermosetting resin and an inorganic filler, and [tablet density (g / cm ³ )].
/ Density of cured resin (g / cm ³ )] × 100%. Here, the above tablet density is
The weight of the tablet (g) / the volume of the tablet (cm ³ ), and the above-mentioned cured resin density is obtained by the weight of the cured resin (g) / the volume of the cured resin (cm ³ ). Can be

[0011]

DETAILED DESCRIPTION OF THE INVENTION The composition for resin tablet molding used in the present invention is an epoxy resin as a thermosetting resin.
And novolak-type phenolic resin as its curing agent
If further an essential component and an inorganic filler, 必 thereto
If necessary, additives such as a curing accelerator, a silane coupling agent, a release agent, and a coloring agent are added, and the mixture is mixed with or without heating.

The composition usually has an average particle diameter of 0.1 to
By pulverizing to about 0.5 mm and compression molding at room temperature according to a conventional method, it is generally suitable for a runnerless type transfer molding and has a cross-sectional diameter of 4.5 to 25 mm and a height of 5 to 30 mm.
The resin tablet has a columnar shape, but the tablet may have another shape such as a prismatic shape in addition to the cylindrical shape.

In the present invention, as described above, the melt viscosity of such a resin tablet is in the range of 500 to 1,000 poise at the temperature of a molding die (usually 150 to 200 ° C., preferably 160 to 190 ° C.). Is set as the largest feature point. In other words, when the viscosity is set in such a range, this is put into a pot and gated.
The air entrainment at the time of melt-pressing the cavity through the cavity is suppressed, so that the inside of the sealing resin that is melt-pressed into the cavity and cured so as to cover the semiconductor element assembly structure disposed therein is Almost no voids are observed. In addition, in the above viscosity range, there is no possibility that the fluid resistance applied to the semiconductor element assembly when melt-pressed into the cavity becomes excessively large, and there is no particular concern that the structure is physically damaged.

On the other hand, a conventional resin tablet is
Since the above melt viscosity was set to a low value of usually 200 poise or less from the viewpoint of melt indentation, entrainment of air at the time of pot injection was inevitable, which caused many voids in the sealing resin. I think that the. As the melt viscosity increases, the above problem decreases, but less than 500 poise still does not provide satisfactory results. On the other hand, if the melt viscosity is too high and exceeds 1,000 poise, which is out of the specified range of the present invention, the fluid resistance becomes large, and the breaking and bending of the bonding wire in the semiconductor element assembly occurs. And other critical defects such as short circuit failure.

The melt viscosity of the resin tablet of the present invention is
The above-mentioned specific range can be easily set, for example, by appropriately adjusting the melt viscosity of the thermosetting resin to be used and the amount of the inorganic filler used. The most typical thermosetting resin is an epoxy resin,
The melt viscosity of this epoxy resin is 1 in consideration of the mold temperature.
It is generally preferred that the temperature be in the range of 15 to 30 poise at a temperature of 50 ° C. In addition, as the amount of the inorganic filler increases, the melt viscosity of the tablet increases, but it is generally preferable that the amount of the inorganic filler be in the range of 72 to 80% by weight of the tablet, that is, the composition. The melt viscosity of the epoxy resin means a value measured by an Oswald viscometer.

As such an epoxy resin, a cresol novolak type epoxy resin or a halogenated phenol novolak type epoxy resin having an epoxy equivalent of 175 to 300 can be preferably used. In the case of an epoxy resin, an appropriate curing agent is required. Preferred examples of the curing agent include novolac type phenol resins such as cresol novolak resin and phenol novolak resin. Curing accelerators commonly used with these curing agents include 2-methylimidazole, boron trifluoride,
And triphenylphosphine.

As the above-mentioned inorganic filler, quartz glass powder, silicon dioxide powder and the like are preferably used. Other conventionally known calcium silicate, aluminum nitride, zirconium oxide, clay, calcium carbonate, antimony oxide It is also possible to use powders of, for example, alumina, silicon carbide, and glass fibers. In general, the average particle diameter of the inorganic filler is preferably about 5 to 20 μm.

The resin tablet of the present invention is characterized in that it has a melt viscosity in a specific range as described above, and has a tableting density, that is, a molding density at room temperature compression molding from a composition powder of 90% or more. Preferably, it is 93% or more. If the tableting density is lower than 90%, the air content at the time of pouring the pot is increased, and the effect of reducing the voids by defining the melt viscosity is impaired.

Next, a method of resin-sealing a semiconductor by a runnerless transfer molding using the resin tablet having the above-described structure according to the present invention will be described with reference to FIGS.

FIG. 1 shows a cross-sectional structure of a transfer molding die of a runnerless type comprising an upper die 10 and a lower die 11, wherein a plurality of pots are provided at predetermined intervals in the direction perpendicular to the paper. 1 and a gate 3 having one end directly connected to each of the pots 1 and the other end directly connected to the cavities 2 (2a, 2b).
(3a, 3b), and each pot 1 is provided with a plunger 4.

The size of each of the above components differs depending on the size of the semiconductor to be resin-sealed. For example, the pot 1 is designed to have a shape and size corresponding to the resin tablet 7, and No. 3 usually has a cross-sectional area of 0.6 to 1.
It is designed to be 0 mm ² and generally 5 to 15 mm long. In addition, this size is shown in FIGS.
This is substantially the same even when using other molding dies as shown in FIG.

The above cavity 2 of such a molding die
a, 2b, a plurality of semiconductor elements disposed at predetermined intervals in the direction perpendicular to the paper of the lead frames 5a, 5b, and a semiconductor element assembly structure including external leads and bonding wires surrounding the semiconductor elements. 6a, 6b (for example, 16 Pin
DIPs, 42-pin DIPs, power transistors, etc.) are arranged, and the resin tablet 7 of the present invention is put into each pot 1, and is pressed by the plunger 4 while being heated at the mold temperature. The mold temperature at this time is usually 150 to 200 ° C, preferably 160 to 190 ° C, as described above. The plunger pressure is generally 50 to 120 kg / cm ² , preferably 70 to 1 kg / cm ² .
It is set to 00 kg / cm ² .

The resin tablet 7 is melted by the above-mentioned heating and pressing, and the cavity 2 is formed via the gates 3a and 3b.
a and 2b, and is cured in a state where the semiconductor element assembly structures 6a and 6b disposed here are entirely covered. At this time, since the melt viscosity and the tableting density of the resin tablet 7 are within the above-mentioned specific ranges, almost no voids are found in the cured resin, and there is no possibility of causing physical damage to the assembly structures 6a and 6b. Absent.

FIG. 2 shows a state in which the transfer molding has been performed as described above, and the mold has been released from the molding die composed of the upper die 10 and the lower die 11. Reference numerals 20a and 20b denote the leads, respectively. It is a hardened sealing resin which covers the semiconductor element assembly structures 6a, 6b disposed at predetermined intervals on the doframes 5a, 5b. Here, 30a and 30b are resins cured in the respective gates 3a and 3b, and 100 is a resin cured in the respective pots 1. These resin parts 30a, 30b, and 100 cause molding loss. However, since there is no runner, there is no resin loss at the runner part, and the material cost can be reduced accordingly.

In the molding die shown in FIG.
In this configuration, the cavities 2a and 2b are directly connected to the other ends of the gates 3a and 3b, one ends of which are directly connected to the one pot 1. However, the cavities are directly connected to one pot 1 via the gate 3. In general, the number of 2 can be freely selected in the range of 1 to 6, preferably 2 to 4. For example, FIGS. 3A and 3B show this example.

That is, as shown in FIG. 3A, four cavities 2c, 2d, 2e and 2f are directly connected to one pot 1 via gates 3c, 3d, 3e and 3f. Also, as shown in FIG. 3 (B), gates 3g and 3h, one end of which is directly connected to one pot 1, are each made into a bifurcated shape, and two cavities 2g are provided at both ends thereof.
A configuration in which 2g ′ and 2h, 2h ′ are directly connected may be adopted.

[0027]

As described above, in the present invention, the melt viscosity and the tableting density of the resin tablet for runnerless transfer molding are set to specific ranges so that the semiconductor element assembly can be formed at the time of molding. Voids inside the sealing resin can be reduced without causing damage, thereby making it possible to obtain a resin-sealed semiconductor device having excellent moisture resistance reliability and the like.

[0028]

Next, an embodiment of the present invention will be described in more detail. Hereinafter, “parts” means “parts by weight”.

Example 1 Epoxy equivalent of 19 with a melt viscosity of 25 poise at 150 ° C.
20 parts of cresol novolak type epoxy resin (hereinafter referred to as epoxy resin A), 10 parts of novolak type phenolic resin, 96 parts of silicon dioxide powder, 0.5 part of 2-methylimidazole, and 0 parts of carnauba wax 0.5 part, 0.5 parts of carbon black and 0.5 parts of a silane coupling agent were mixed, heated and kneaded with a heating roll at 90 ° C. for 5 minutes, and then cooled and pulverized to obtain an average particle diameter of 0.1 part. An epoxy resin composition powder of about 0.5 mm was obtained.

This powder is subjected to room temperature compression molding using a tableting machine.
A cylindrical resin tablet having a sectional diameter of 9.8 mm, a height of 13 mm, and a weight of 1.77 g was produced. 17 of this tablet
The melt viscosity at 5 ° C. was 800 poise and the tablet density was 95%. This tablet was used as the resin tablet for semiconductor encapsulation of the present invention.

Example 2 The epoxy resin composition powder prepared in Example 1 was subjected to room temperature compression molding using a tableting machine to obtain a cross-sectional diameter of 9.8 mm and a height of 14.2.
A cylindrical resin tablet having a diameter of 1.75 g and a weight of 1.75 g was produced. The tablet had a melt viscosity at 175 ° C. of 805 poise and a tableting density of 90%. This tablet was used as the resin tablet for semiconductor encapsulation of the present invention.

Example 3 In place of the epoxy resin A, the melt viscosity at 150 ° C. was 1
An epoxy resin composition powder was prepared in the same manner as in Example 1 except that the same amount of a 5-poise cresol novolak type epoxy resin having an epoxy equivalent of 195 was used, and this powder was subjected to room temperature compression molding using a tableting machine. , Cross section diameter 9.8mm, height 1
A cylindrical resin tablet having a size of 4.2 mm and a weight of 1.75 g was produced. The melt viscosity of the tablet at 175 ° C. is 5
At 70 poise, the tablet density was 90%. This tablet was used as the resin tablet for semiconductor encapsulation of the present invention.

Comparative Example 1 In place of epoxy resin A, the melt viscosity at 150 ° C. was 5
An epoxy resin composition powder was obtained in the same manner as in Example 1 except that the same amount of cresol novolak type epoxy resin having an epoxy equivalent of 195 was used and the amount of silicon dioxide powder used was changed to 75 parts. Was. This powder was subjected to room temperature compression molding using a tableting machine, and had a cross-sectional diameter of 9.8 mm and a height of 14.
A cylindrical resin tablet having a size of 2 mm and a weight of 1.75 g was produced. The melt viscosity of the tablet at 175 ° C. was 120.
In poise, the tablet density was 90%. This tablet was used as a resin tablet for semiconductor encapsulation for comparison.

Comparative Example 2 An epoxy resin composition powder was obtained in the same manner as in Example 1 except that the amount of silicon dioxide powder used was changed to 128 parts. This powder was subjected to room temperature compression molding using a tableting machine to produce a cylindrical resin tablet having a cross-sectional diameter of 9.8 mm, a height of 14.2 mm, and a weight of 1.75 g. 175 of this tablet
Melt viscosity at 1500C is 1,500 poise and tableting density is 90
%. This tablet was used as a resin tablet for semiconductor encapsulation for comparison.

Next, a semiconductor was resin-sealed by a runnerless transfer molding using each of the resin tablets according to the above Examples and Comparative Examples, and the performance was examined. The molding die having the structure shown in FIG. 1 was used. The number of pots is 103, and therefore the number of cavities is 20, the size of each gate is 0.7 mm ² in cross section, 7 mm in length, and the capacity of each cavity is 402 mm ³ .

On the two lead frames arranged in this molding die, ten semiconductor element assembly assemblies are arranged at predetermined intervals, and these assemblies are fixed so as to be located in each cavity. Be done. The mold temperature is 1
At 80 ° C., the plunger pressure was 90 kg / cm ² , and the plunger speed was 1.85 mm / sec. Depending on the temperature of the mold, the resin tablet is usually heated to a temperature of 175 to 180 ° C.

With respect to the semiconductor device thus sealed with resin, the number of voids in the resin-sealed portion and the damage to the semiconductor device were examined. The results are shown in Table 1 below.
The number of voids was obtained by taking a photograph with a soft X-ray apparatus and examining the number of voids having a diameter of 0.2 mm or more. The damage of the semiconductor device was determined by examining whether an abnormality such as disconnection or bending of the bonding wire in the semiconductor element assembly was observed by soft X-ray photography.

[0038]

[Table 1]

As is evident from the results shown in Table 1, according to the resin tablet of the present invention, it is possible to manufacture a highly reliable resin-encapsulated semiconductor device having few voids and no semiconductor damage. Can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a runnerless transfer molding die to which a resin tablet of the present invention is applied.

FIG. 2 is a plan view showing a state in which the semiconductor is resin-sealed using the above-mentioned molding die and then released from the molding die.

FIGS. 3 (A) and 3 (B) are configuration diagrams each showing a modified example of the molding die of FIG. 1 in which the connection state of the pot, the gate and the cavity is different.

[Explanation of symbols]

1 pot 2 (2a, 2b, 2c, 2d, 2e, 2f, 2g, 2g
', 2h, 2h') Cavity 3 (3a, 3b, 3c, 3d, 3e, 3f, 3g, 3
h) Gate 6a, 6b Semiconductor element assembly structure 7 Resin tablet 10, 11 Mold 20a, 20b Sealing resin

Claims (3)

(57) [Claims] 1. A molding die having a pot and a gate having one end directly connected to the pot and the other end directly connected to a cavity in which a semiconductor element assembly is arranged is inserted into the pot through the gate. In the resin tablet for semiconductor encapsulation melt-pressed into the cavity, an epoxy resin as a thermosetting resin and a resin as a curing agent thereof are used.
It is composed of a composition containing a volatile phenolic resin and an inorganic filler, and has a melt viscosity at a mold temperature for the above-mentioned melt injection in the range of 500 to 1,000 poise and a tableting density. Is 90% or more. 2. The resin tablet for encapsulating a semiconductor according to claim 1, wherein the tablet density is 93% or more. 3. The inorganic filler has an average particle size of 5 to 20.
The resin tablet for semiconductor encapsulation according to claim 1 or 2, wherein the thickness is about μm.