JPH08162486A - Resin-sealing of semiconductor element - Google Patents

Abstract

PURPOSE: To prevent the warpage of a package by a method wherein when a semiconductor element is resin-sealed by a transfer molding method, a sealing resin preform is previously pressed and transferred to the vicinity of a gate at the molding temperature of a sealing resin and after a flow of the sealing resin is stopped or is maintained in the state close to a state that it is stopped for a prescribed time for gelling at the molding temperature of the resin, the element is subjected to pressure molding. CONSTITUTION: When a semiconductor element is resin sealed by a transfer molding method, a sealing resin perform heated to the molding temperature of sealing resin 9 is previously pressed and transferred to the vicinity of a gate 5 of a metal mold 2 and after a flow of the sealing resin 9 is maintained in the vicinity of the gate 5 in a state that it is stopped for a prescribed time for gelling at the molding temperature of the sealing resin 9, the resin 9 is again pressed to make the resin 9 flow in a cavity 6, in which the element is arranged, and this semiconductor element is resin-sealed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of resin-sealing a semiconductor element by transfer molding, and more particularly, in the production of a single-sided molded package, the resin-sealing of a semiconductor element capable of preventing the warp of the package and resin-sealing Regarding the method.

[0002]

2. Description of the Related Art Recently, the problems to be solved by the invention
Most of the semiconductor packages are surface-mounted, and further miniaturization, thinning, and weight reduction are progressing, and the packaging density on the substrate is dramatically increasing. However, on the other hand, thinning and BG
Single-sided packages such as A (ball grid array) packages have also been developed. These packages have a big problem that the packages warp during molding due to the difference in expansion coefficient between the sealing resin and the substrate material or lead frame. When the package is warped, the leads and the solder balls do not exist on the plane, so that the leads and the balls cannot be completely connected to the substrate when mounted on the substrate, which is a serious problem.

In order to solve such a problem, various studies have been made from the side of the sealing resin, but such a problem cannot be completely solved only by improving the sealing resin.

The present invention has been made in view of the above circumstances.
It is an object of the present invention to provide a resin encapsulation method for a semiconductor element, which is capable of resin-encapsulating a single-sided molded package or the like by preventing warpage as much as possible by a transfer molding method.

[0005]

Means and Actions for Solving the Problems The present inventor has studied how to prevent the warp of the semiconductor package from the viewpoint of the molding method. That is, the semiconductor element has been conventionally molded and sealed using a one-pot type transfer molding machine or a multi-pot type transfer molding machine. Recently, a large number of multi-pot type molding machines have been used to improve the use efficiency of resins and to cure them for a short time. In this transfer molding, the encapsulating resin preform (tablet) is preheated to the molding temperature, and the encapsulating resin preform heated to this molding temperature is pressed by the plunger to place the semiconductor element from the mold gate. The semiconductor element is made to flow into the mold cavity and is sealed with resin by pressure molding. The present inventor conducted a detailed study on molding conditions and package warpage using a transfer molding machine. Even if the (tablet) is preheated, due to the non-uniformity of the temperature inside the resin preform (tablet) at the time of molding, uneven temperature will occur in the resin that has flowed into the cavity in the conventional molding method, and the curing reaction will proceed uniformly. First, I found that the package warped.

As a result of further studies based on this finding, it was found that the conventional encapsulating resin preform heated to the molding temperature is not forced to flow into the cavity of the mold through the gate at a stroke as in the prior art. First, the encapsulating resin preform heated to the molding temperature is pressure-transferred to the vicinity of the gate of the mold, where the encapsulating resin is stopped for a predetermined time within the gelation time of the encapsulating resin at the molding temperature ( The present invention has been made based on the knowledge that package warpage can be prevented by transferring the semiconductor element by transfer molding after maintaining it in a completely stopped state or a state close to a completely stopped state). .

Therefore, according to the present invention, when the semiconductor element is resin-sealed by transfer molding, the sealing resin preform heated to the pre-molding temperature is pressure-transferred to the vicinity of the gate of the mold, and the vicinity of the gate is transferred. In the above, after maintaining the encapsulating resin in a stopped state for a predetermined time within the gelling time at the molding temperature of the encapsulating resin, the encapsulating resin is re-pressurized to flow into the cavity in which the semiconductor element is arranged. Provided is a resin sealing method for a semiconductor element, which is characterized in that the semiconductor element is resin-sealed.

The present invention will be described in more detail below.

The present invention is for resin-sealing a semiconductor element by transfer molding. For example, QFP (quad flat package), TQFP (sink quad flat package), TSOP (thin small outline package), BGA (ball grid array). ) Are suitable for sealing surface mount packages. Also,
The molding method of the present invention can be applied to any known molding method such as transfer molding or transfer molding in which the molding is performed in a vacuum state.

In the present invention, therefore, in such a semiconductor element sealing method by transfer molding, the sealing resin is pressure-transferred to the vicinity of the gate at the molding temperature in advance, and the gelling time at the resin molding temperature is set. After stopping the flow of the sealing resin during or while maintaining a state close to the stopped state,
It is pressure-molded.

This will be described with reference to FIGS.
3 to 3 are for sealing the TSOP package, FIGS. 4 to 6 are for sealing the BGA package, in which 1 is a plunger of the transfer molding machine, 2 is a mold, 3 is a plunger pot, Reference numeral 4 is a runner, 5 is a gate, 6 is a cavity, 7 is a semiconductor element, 8 is a lead frame or a resin substrate, and 9 is a sealing resin.

First, the preform (tablet) of the pre-sealing resin 9 is set in the plunger pot portion 3 (usually heated to 165 to 180 ° C.) heated to the molding temperature (FIGS. 1 and 4). Immediately, preferably, after being left for several seconds to be preheated, it is pressure-transferred by the plunger 1 to the vicinity of the gate 5 through the runner 4 as shown in FIGS. In this state, the flow of the sealing resin 9 is temporarily stopped (in the present invention, the stopped state means a substantially stopped state, and includes a completely stopped state and a state close thereto), and sealing Let stand during the gel time of the resin. As a result, the temperature distribution of the resin 9 can be made uniform by partially fluidizing the sealing resin 9 that has not been uniformly heated by preheating. The gelling time of the sealing resin depends on the molding temperature 175.
It is about 15 to 25 seconds at a temperature of ℃. Therefore, the standing time is usually 10 seconds or less and 0.5 seconds or more, and preferably 5 seconds or less and 1 second or more. If it is longer than 10 seconds, the sealing will thicken within the standing time, resulting in wire deformation or unfilling, and if it is shorter than 0.5 seconds, the resin temperature may not be uniform and the package may warp after molding. .

Then, the plunger 1 is lowered again to pressurize the sealing resin 9 and transfer it into the cavity 6,
The encapsulating resin 9 is cured for a minute to encapsulate the semiconductor element 7 (FIGS. 3 and 6). Then, when the curing reaction is completed,
Open the mold and take out the molded package.

FIG. 7 shows the descent profile of the plunger in the conventional method and the method of the present invention. In the conventional molding method, the plunger descends with the start of molding, and the plunger is almost linear until the cavity is completely filled. The jar keeps descending. The present invention illustrates the lowering of the plunger in FIG.
It is temporarily stopped in the state of No. 5, and is lowered again after a lapse of a predetermined time.

In the above-mentioned molding method, it is more effective to lower the molding temperature against the warp, but from the viewpoint of productivity, the range of 160 to 190 ° C. is desirable. Especially 160
C. to 175.degree. C. is a desirable range from the viewpoint of curability and warpage.

The molding pressure is 30 Kg / mm ² to 10
0 kg / mm ² , particularly preferably 40 to 70 kg / mm
² 30kg / mm unfilled with the molding pressure is too low at less than ² tends to occur, and if the inside the package exceeds 100 Kg / mm ² have sensitive element to the pressure,
The characteristics may change.

As the encapsulating resin, any encapsulating resin that is generally commercially available can be used, but in the present invention, an epoxy encapsulating material composed of the following constituents is particularly preferable. Can be used for.

That is, this epoxy encapsulating material (epoxy encapsulating resin composition) contains an epoxy resin, a phenolic resin as a curing agent for the epoxy resin, and an inorganic filler, and the main epoxy resin is one molecule. Any may be used as long as it has at least two epoxy groups.
For example, bisphenol A type epoxy resin, novolac type epoxy resin, alicyclic epoxy resin, glycidyl type epoxy resin, biphenyl type epoxy resin, naphthalene ring-containing epoxy resin, cyclopentadiene-containing epoxy resin, etc. are used. May be combined. These epoxy resins have a softening point of 50 to 10
Those having an epoxy equivalent of 100 to 400 at 0 ° C are desirable. Further, a brominated epoxy resin can be used for flame retardancy.

Phenolic resins which act as curing agents for epoxy resins include phenolic hydroxyl groups such as phenol novolac resins, cresol novolac resins, triphenol methane, phenol aralkyl resins, naphthalene ring-containing phenol resins and cyclopentadiene-containing phenol resins. The thing which has more than one is mentioned. Among the phenolic resins, those having a softening point of 60 to 120 ° C. are preferable. 90-150 as the hydroxyl equivalent
The thing of is desirable. The phenol resin may be used in any amount as long as the equivalent ratio of epoxy group to hydroxyl group is in the range of 0.5 to 2, but is usually 30 to 100 parts by weight, preferably 40 to 70 parts by weight per 100 parts by weight of the epoxy resin. Parts by weight. If it is less than 30 parts by weight, sufficient strength cannot be obtained,
On the other hand, if it exceeds 100 parts by weight, unreacted phenol resin remains and moisture resistance is reduced.

The encapsulating resin composition used in the present invention contains an inorganic filler. The inorganic filler reduces the expansion coefficient of the sealing material and reduces the stress applied to the semiconductor element. As specific examples, crushed and spherical fused silica and crystalline silica are mainly used. In addition to these, alumina, silicon nitride, aluminum nitride, etc. can also be used. The average particle size of the inorganic filler is preferably 5 to 20 μm. The filling amount of the inorganic filler is preferably 200 to 2100 parts by weight, and if it is less than 200 parts by weight, the expansion coefficient increases, the stress applied to the semiconductor element increases, and the element characteristics deteriorate. Again 2100
If it exceeds the weight part, the viscosity at the time of molding becomes high and the moldability deteriorates. In order to achieve both low expansion of the cured product and moldability, it is better to use a blend of spherical and crushed products, or to use only spherical products. This type of inorganic filler is preferably surface-treated with a silane coupling agent before use.

Typical examples of the curing catalyst for epoxy resin and phenol resin include imidazole or its derivative, phosphine derivative and cycloamidine derivative. The amount of catalyst is 0.001 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the epoxy resin. If it is less than 0.001 part by weight, it cannot be cured in a short time, and if it exceeds 5 parts by weight, the curing rate is too fast to obtain a good molded product.

A silicone-based flexibility-imparting agent may be added to the encapsulating resin composition to reduce stress. For example, a silicone rubber powder, a silicone gel, a block polymer of an organic resin and a silicone polymer, or the like can be blended, and the surface of the inorganic filler may be treated with a two-component type silicone rubber or silicone gel. Usually, the amount of this type of stress reducing agent used is 0.5 to 10%, preferably 1 to 5% of the total system. If it is less than 0.5%, sufficient impact resistance is not given, and if it exceeds 10%, the mechanical strength becomes insufficient. Furthermore, silane coupling agent, antimony oxide,
You may mix | blend a phosphorus compound etc. with a sealing resin composition.

By using the encapsulating resin composition of this kind of composition and molding by the encapsulating method described above, a package with less warpage can be obtained.

[0024]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Examples and Comparative Examples A 1.4 mm-thick TSOP package using a 32-pin copper frame and a 24-sided 1.5 mm-thick BGA package using a BT resin as a substrate are shown in FIGS. As shown in FIGS. 6A to 6C, it was sealed with a commercially available epoxy sealant. The epoxy encapsulants used were KMC240 and KMC216 (both manufactured by Shin-Etsu Chemical Co., Ltd.), and their general characteristics are shown in Table 1. In addition, molding uses a multi-pot type transfer molding machine,
The molding conditions are as shown in Table 2. Table 2 shows the results of the amount of warpage of the package after molding. The method of evaluating the amount of warpage is as follows.

Warpage amount of package: After molding and post-curing (175 ° C./6 hours), five packages were used, and the warpage in the diagonal line of each package was measured and averaged. In the case of the TSOP package, 8 μm or less and in the case of the BGA package, 20 μm or less were judged as acceptable products by the mounting test on the substrate.

[0027]

[Table 1]

[0028]

[Table 2]

FIG. 7 shows the relationship between the plunger descent distance and time in Example 2 and Comparative Example 1.

From the results shown in Table 2, it was confirmed that the warp of the package was remarkably improved by adopting the resin sealing method of the present invention.

[0031]

According to the present invention, when the semiconductor element is resin-molded by transfer molding, the sealing resin is pressure-transferred to the vicinity of the gate at the molding temperature in advance during the gelling time at the resin molding temperature. Warping of the package can be prevented by performing pressure molding after the flow of the sealing resin is stopped or maintained in a state close to the stopped state.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating a preheating step when a TSOP package is resin-sealed according to the method of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating the resin flowing step.

FIG. 3 is a schematic cross-sectional view illustrating the pressure molding step.

FIG. 4 is a schematic cross-sectional view illustrating a preheating step when resin-sealing a BGA package according to the method of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating the resin flowing step.

FIG. 6 is a schematic cross-sectional view illustrating the pressure molding step.

FIG. 7 is a schematic diagram for explaining a lowered state of the plunger according to the method of the present invention and the conventional method.

[Explanation of symbols]

 1 Plunger 2 Mold 3 Plunger pot part 4 Runner 5 Gate 6 Cavity 7 Semiconductor 8 Lead frame or substrate 9 Sealing resin

Claims (1)

[Claims] 1. When resin-sealing a semiconductor element by transfer molding, a sealing resin preform heated to a preforming temperature is pressure-transferred to the vicinity of a gate of a mold, and the sealing is performed near the gate. After maintaining the resin in a stopped state for a predetermined time within the gelling time at the molding temperature of the sealing resin, the sealing resin is repressurized to flow into the cavity in which the semiconductor element is arranged, A resin encapsulating method for a semiconductor element, which comprises encapsulating.