JP3344832B2 - Resin flow prediction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting the behavior of a resin when the resin is injected into a cavity of a mold in which a structure is movably arranged, and more particularly to a sealing material for a semiconductor integrated circuit. The present invention relates to a method of predicting the behavior of a resin used in a mold.

[0002]

2. Description of the Related Art Semiconductor integrated circuit components (IC, LSI, etc.)
Is to place the chip on which the electronic circuit is formed on a metal plate called an island, place the lead and chip in a mold cavity with the lead and chip connected by a gold wire, and apply thermosetting sealing resin. Molded by pouring. In order to ensure the sealing performance, it is necessary that the entire cavity is filled with the resin in the molding process.

However, in recent years, in response to the downsizing and higher functionality of electronic devices, ICs have become thinner, have more pins, and have larger chips. It is getting smaller and the flow resistance is increasing,
The rate of occurrence of defects such as generation of unfilled voids, island shift in which the island moves due to the flow of the resin, short-circuiting due to deformation of the gold wire, and disconnection is increased.

In order to remove such defects, it is important to accurately grasp the behavior of the resin in the cavity during the molding process. If the technology to predict the flow of resin in the cavity is established, systematic calculation and prediction of the behavior of the resin for various molding conditions and mold dimensions based on the flow prediction by computer,
For example, it is possible to predict the structure of the chip, the shape of the mold, the formulation of a sealing resin having excellent fluidity in the mold, and the like.

[0005]

However, with respect to a multi-pin, large chip, and thin part, the conventional flow prediction method that treats a structure such as a chip disposed in a mold as a fixed object has a calculation result. And the behavior of the resin at the time of actual molding does not match. This is considered to be due to the fact that the chip moves in the mold due to the uneven distribution of the internal resin pressure generated during the filling process, and the flow path is deformed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a method for predicting the flow of a resin, which can accurately predict the behavior of the resin in a mold by considering the deformation of the flow path. With the goal.

[0007]

According to the method of the present invention, a flow prediction step for calculating a behavior of a resin at a given filling rate X, and a behavior is predicted by the flow prediction step. Calculating the stress acting on the structure by calculating the internal pressure of the resin, and a structural analysis step of calculating the deformation of the flow path due to the movement of the structure, the deformed flow path as a new flow path, The flow prediction step and the structural analysis step are repeatedly executed until the deformation of the flow path at the filling rate X converges, and a new unit filling rate ΔX is added to the filling rate X to add a new unit filling rate when the flow path deformation converges. It is assumed that the filling rate X is 10
The process is characterized in that the process is repeated until it reaches 0%.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for predicting resin flow according to the present invention will be described below. In the embodiment, the behavior of the resin in the mold cavity is predicted for the integrated circuit component.

As shown in FIG. 1, an integrated circuit component is generally mounted on a chip 1 on which a circuit is formed on an island 2, and a lead 3 and the chip 1 are joined together by a metal wire 4 in a mold. It is configured by being sealed with a resin 5 poured into the inside.

[0010] As shown in FIG.
The resin 5 is injected from the gate 11 located on the lower side of the island 2 and is filled in the space on the lower side of the island 2 and mainly into the space on the upper side of the island 2 through the gap S between the island 2 and the lead 3. Is also wrapped around and filled. As the resin 5 is charged, the air in the mold 10 is discharged from an air vent 12 provided on the opposite side of the gate 11.

The resin injected into the cavity flows separately above and below the island 2 and the chip 1, but the flow is faster at the lower side of the island 2 than at the upper side due to less flow resistance. For this reason, the pressure on the lower side becomes relatively high, and a moment acts to lift the island 2 from below.

Considering only this moment, chip 1
Will always collide with the upper wall of the cavity, but in many cases will not actually collide. This is expected because the resin flowing upward functions as a cushion.

In the prediction method of the embodiment, while the behavior of the resin is predicted by the flow prediction program, the deformation of the flow path is considered at each stage of filling by the structural analysis program, and the flow prediction is performed again based on the deformed flow path. Execute. In addition, the internal pressure of the resin is used as the driving force for the deformation, and the elasticity of the island, which is the structure, and the elasticity of the resin that has wrapped around the back of the structure when viewed from the gate into which the resin is injected are used as the resistance to the deformation. I have.

Next, a prediction method according to the embodiment will be described with reference to FIG.

As a first step, a flow path model for flow calculation is created. For example, when a model of a semiconductor component sealing structure is used as a model, the shape in the mold cavity, the arrangement of islands, chips and gold wires, the position of gates for injecting resin, and the positions of air vents for venting air, etc., are taken into consideration. To create a flow channel model.

As a second step, a resin characteristic model, flow initial conditions and boundary conditions are input. The resin is modeled, for example, from the following characteristics.

(1) Dependence of viscosity on shear rate, temperature, and degree of cure (2) Dependence of degree of cure on temperature and time (3) Specific heat, thermal conductivity, fluid density

The initial flow conditions and boundary conditions are, for example, the temperature, flow rate, pressure and the temperature of the mold at the position where the resin flows.

In the third step, the flow calculation from the filling rate 0 to the current filling rate X (X = ΔX in the initial state) is executed. For this flow calculation, a commercially available general flow prediction program can be used. ΔX is a filling rate which is a unit for predicting the flow path deformation, and thereafter, repeatedly predicts the flow path deformation while adding ΔX. The unit filling rate ΔX is set to such an extent that an error between the flow path deformation calculated as the filling proceeds and the actual flow path deformation does not increase.

In a fourth step, internal pressures at all positions inside the filled resin are calculated, and in a fifth step, a structural model for deformation analysis is created based on the calculated internal pressures. At this time, the resin wrapping around the back side of the structure when viewed from the gate side, for example, the resin wrapping around the upper side of the island is also modeled. A model of a structure, for example, a chip or an island is also input.

In a sixth step, a deformation analysis is performed based on the structural model. For this deformation analysis, a commercially available general structural analysis program can be used. The driving force of the deformation used in the analysis is the internal pressure of the resin, and the resistance to the deformation is the elasticity of the structure and the elasticity of the resin that has wrapped around the back of the structure.

When the resin behaves as a liquid, that is, when it is considered as a model flowing from a gate, it is not necessary to consider it as a drag element. If compressed, it must be taken into account as a drag factor.

When a general elastic body such as rubber is used as a model, a linear analysis is possible because a reaction force is generated during both compression and tension. Although it sometimes functions as an elastic body, a linear force cannot be analyzed because a reaction force does not act during tension.
Therefore, in the method of the embodiment, a non-linear analysis is performed on the portion of the drag component that is modeled on the resin, taking into account the reaction force only during compression and excluding this effect during tension. However, a linear analysis program can be used if a step of determination is made so that the drag of the resin is not taken into account during tension.

In the seventh step, the dimensions of the flow path model for flow analysis are changed using the displacement of the structure, that is, the lifting of the island or the like as the flow path deformation.

In an eighth step, it is determined whether or not the flow path deformation at the filling rate X has converged by comparing the previous flow path with the previous flow path. , The third to seventh steps are executed again. If it is determined that the flow path deformation at the filling rate X has converged, the process proceeds to the ninth step.

FIG. 4 shows an example of the displacement of the island used for the judgment in the eighth step. The straight line in FIG. 4 shows how much the end of the island on the gate side and the air vent side is displaced from the design position, and the vertical axis shows the amount of displacement. In this example, three times at a filling rate of 50%,
At 70%, it can be determined that the flow path deformation has almost converged by repeating four times.

In the ninth step, it is determined whether or not the filling rate X has reached 100%. If not, the flow path where the deformation converges at the filling rate X is defined as the basic flow path. The third step to the eighth step are repeatedly executed with X + ΔX obtained by adding the unit filling rate ΔX as a new filling rate X.

If it is determined in the ninth step that the filling rate has reached 100%, the flow prediction processing of the resin is terminated. In the flowchart of FIG. 3, a method of repeatedly calculating the flow from the filling rate 0 to the section X while adding the unit filling rate ΔX to the filling rate X is adopted, but after the calculation at the filling rate X is completed. , The next stage is X to X +
It is also possible to adopt a method of calculating only the newly added section up to ΔX and increasing the filling rate stepwise by integration with the previous calculation.

Next, a description will be given of a method of measuring the drag of a resin functioning as a drag against deformation in the deformation analysis executed in the sixth step. The drag of the resin is
For example, as shown in FIG. 5, it can be detected by sandwiching a resin between two opposed disks, pushing up the lower disk at a constant speed, and measuring the load acting on the upper disk.

The load detected from the upper disk, that is, the drag of the resin, increases as the distance between the disks becomes smaller, as shown in the graph of FIG. 6, for example. The value of the detected drag can be converted to the internal pressure by dividing it by the cross-sectional area of the disk, and converted to an elastic modulus that shows how the internal pressure of the resin changes when it is pushed in a small amount. You can also.

When the drag is measured by the apparatus shown in FIG. 5, when the compressive force exceeds a certain value, the resin flows to the side of the disk. The point at which the flow starts is defined as the yield position as shown in FIG. 7, and at this point the elastic modulus decreases. The yield position appears at low pressure when the shear rate is high and at higher pressure when the shear rate is low. What is used as a model for the drag is the modulus of elasticity in the compression region up to the yield position.

FIG. 8 shows the result (a) of the prediction calculation of the embodiment.
(b), results (c) and (d) at the time of actual molding, and results (e) and (f) of the conventional prediction calculation without considering the flow path deformation. (a), (c) and (e) show the progress of the resin on the upper surface of the chip, and (b), (d) and (f) show the progress of the resin on the lower surface.

On the upper surface side, almost the same results as in the actual molding are obtained in both the method of the embodiment and the conventional method. On the other hand, for the lower surface, unfilled voids generated at the time of actual molding are predicted by the method of the embodiment, but unfilled voids are not predicted by the conventional method. Thus, it can be understood that the prediction accuracy is improved by considering the flow path deformation.

[0034]

As described above, according to the present invention, the behavior of the resin injected into the mold can be more accurately determined by repeatedly executing the calculation of the flow of the resin and the structural analysis of the flow path deformation. The simulation result can be predicted, and a simulation result almost coincident with the actual molding time can be obtained. Therefore, in the field of integrated circuit components, it is possible to accurately analyze molding conditions which do not cause defects such as generation of unfilled voids and gold wire flow.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a general configuration of an integrated circuit component.

FIG. 2 is an explanatory view showing an arrangement of structures arranged in a mold when manufacturing an integrated circuit.

FIG. 3 is a flowchart illustrating a method for predicting resin flow according to an example.

FIG. 4 is a graph showing the displacement of an island.

FIG. 5 is an explanatory view of an apparatus for measuring a drag of a resin.

6 is a graph showing a relationship between a drag measured by the apparatus shown in FIG. 5 and a disc interval.

FIG. 7 is a graph showing the relationship between the internal pressure and the elastic modulus of the resin.

FIG. 8 is an explanatory diagram comparing simulation results of the example and the conventional example with results of actual molding.

[Explanation of symbols]

 Reference Signs List 1 chip 2 island 3 lead 4 gold wire 5 resin 10 mold 11 gate 12 air vent

Continuation of the front page (56) References JP-A-64-98967 (JP, A) JP-A-1-141020 (JP, A) JP-A 64-67319 (JP, A) JP-A 64-67320 (JP) , A) JP-A-64-67322 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 11/00-11/16 B29C 39/00 B29C 45/02 JICST file (JOIS )

Claims (3)

(57) [Claims] 1. A resin flow prediction method for predicting a behavior of a resin in a process of injecting the resin into a cavity of a mold in which a structure is movably arranged, the method comprising: A flow prediction step of calculating the behavior of the resin; calculating the stress acting on the structure by calculating the internal pressure of the resin whose behavior is predicted by the flow prediction step, and deforming the flow path due to the movement of the structure The flow prediction step and the structural analysis step are repeatedly performed until the deformation of the flow path at the filling rate X converges. When the flow path deformation converges, a predetermined unit filling rate ΔX is added to the filling rate X.
And a process is repeated until the filling rate X reaches 100% by returning to the flow predicting step. 2. In the structural analysis step, the internal pressure of the resin is used as a driving force for deformation, and the elasticity of the structure as a drag against deformation and the back side of the structure as viewed from a gate into which the resin is injected. 2. The method according to claim 1, wherein the elasticity of the wrapped resin is used. 3. In the structural analysis step, a non-linear analysis is performed on a portion of the drag component which is modeled on a resin, taking into account the reaction force only during compression and excluding this effect during tension. 3. The method according to claim 2, wherein the flow of the resin is predicted.