JP2771196B2 - Prediction method of pressure loss in mold and mold flow path design method using the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a mold for molding a thermosetting resin, and more particularly to a mold flow path design method suitable for reducing defects in products.

[Conventional technology]

The conventional method of designing a multi-cavity mold flow path for thermosetting resin is to reduce the runner bottom of the mold gradually in the direction of resin flow and to restrict the gate as described in JP-B-55-17697. The flow path was formed so that the corner was gradually increased corresponding to each cavity moving away from the pot along the runner, so that the total pressure loss at the runner and the gate was constant for each cavity.

[Problems to be solved by the invention]

The above prior art does not consider a method for predicting the flow behavior of a resin flowing while changing the temperature and viscosity in a complicated flow path shape, and it is necessary to actually fill each cavity with the resin at the same speed. Was difficult and the improvement of product quality was limited.

It is an object of the present invention to quickly and accurately simulate the flow state of a resin in a mold to set optimal mold specifications and molding conditions, thereby significantly shortening a product development period and improving product quality. It is to plan.

[Means for solving the problem]

The above object is to divide the mold flow path into a plurality of sections, calculate the flow resistance Q and the flow rate unique to each section in each section, and replace each section with a circular pipe shape, and perform a flow simulation with this shape. , Calculate the temperature, viscosity, flow velocity, and average apparent viscosity a of the resin in each part, and calculate the pressure loss ΔP by ΔP
= ΒaQ to achieve flow prediction. FIG. 1 shows the configuration of this analysis system. In FIG. 1, first, an input unit inputs resin physical property values, molding conditions, and mold channel parameters required for a simulation. Next, the input mold flow path specification data enters the flow path volume calculation section and the section division section, and the volume of the entire flow path and the section to be divided are obtained. The data processed by the section dividing section enters the section volume calculating section and the section shape resistance calculating section, and the flow volume and the shape resistance of each section are obtained. On the other hand, the data processed by the section volume calculation unit enters the tubular flow passage replacement unit,
Each section is replaced with a combination of circular pipe channels. further,
Data processed by the channel volume calculation section and the section volume calculation section,
The data of the transfer time in the molding conditions input to the input section is input to the section flow rate and section passage time calculation section, where the flow rate of the resin passing through each section and the time passing through the section are obtained. Then, by using the data processed by the calculation unit, the data processed by the circular pipe flow replacement unit, and the molding condition data input to the input unit, a flow simulation in the circular pipe is performed, and the resin of each part of the flow path is analyzed. Temperature, viscosity,
Calculate the flow rate, average apparent viscosity, etc. The calculation result in the flow simulation unit enters the viscosity comparison unit. If there is a problem in the result, the simulation is stopped, a part of the input data is changed in the input condition changing unit, and the process returns to the beginning. On the other hand, when there is no problem in the viscosity comparing unit, the average apparent viscosity of each section obtained by the flow simulation, and the pressure loss calculation unit using the flow rate and the shape resistance of each section, and Obtain the accumulated total pressure loss. The result is input to the pressure loss comparing unit. If the calculated pressure loss is larger than the predetermined pressure loss, the input condition changing unit is changed, a part of the input data is changed, and the process returns to the beginning. If the pressure loss comparison section determines that there is no problem,
The output unit outputs final mold flow path specifications, molding conditions, and other necessary information.

[Action]

According to the above method, the shape resistance and the flow rate specific to the flow path are strictly determined by calculating the pressure loss required for the optimal mold flow path design. On the other hand, the flow path is complicated and the flow path is complicated and the calculation time is enormous.Complicated actual machine mold flow path shape is replaced with a combination of circular pipe flow paths, and the average apparent viscosity is calculated. In addition, practically sufficient pressure loss prediction accuracy can be ensured.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. First, a flow simulation method in a circular pipe will be described.

 The isothermal viscosity equation for thermosetting resins is represented by the following model.

Here, η: viscosity, η ₀ : initial viscosity, t ₀ : gel time, c: viscosity increase coefficient, T: absolute temperature, and t: time. Also, η ₀ (T) = aexp (b / T) (2) t ₀ (T) = dexp (e / T) (3) c (T) = f / T−g (4) ). a, b, d, e, f, and g are parameters independent of molding conditions. Equation (1) satisfies the following boundary condition.

When t = 0, η = η ₀ (T) (5) When t = t ₀ (T), η = ∞ (6) The characteristic of equation (1) at an arbitrary temperature T is shown in FIG. .

In most cases, the resin flows in the mold while receiving heat from the tube wall, so that the resin is in a non-isothermal state. Next, a method of estimating the viscosity in this case will be described. First, the following expression is obtained by dimensionlessly rearranging the expression (1).

Here, μ = {η / η ₀ (T)} ^{1 / C (T)} (8) τ = t / t ₀ (T) (9) This curve has the property that μ = 1 at τ = 0 and μ = ∞ at τ = 1. This curve is shown in FIG. Now, in Figure 3, has a mu = mu ₁ with tau = tau _1, In this case, time is t _1, the temperature and T _2. Then, when the time Δt has elapsed, the temperature also increases by ΔT, and the time and the temperature are respectively increased.
A new viscosity at t ₂ and T ₂ will be determined.
From equation (9), τ is a function of t and T, and the increment Δτ of τ up to the new state τ ₂ is obtained by the following equation.

Further, the following expression is obtained from the expressions (9) and (3).

The Δt and ΔT in equation (10) are known in advance as shown in FIG. 3, and T = T _{1 in} equation (11) and T = T ₁ and τ = τ in equation (12).
By substituting ₁ , _one obtains Δτ. Therefore, τ ₂ = τ ₁ + Δτ (13), and μ ₂ is obtained from Expression (7) as τ = τ ₂ .

Then, the following equation is obtained from the equation (8).

η = η ₀ (T) μ ^{C (T)} (15) By substituting the values of T = T ₂ and μ = μ ₂ into this equation (15), Thus, the viscosity η _{2 in} a new state is obtained.

By repeating this method from τ = 0 to 1, it is possible to calculate the change in viscosity from the initial stage in a non-isothermal state to gelation.

In order to analyze the state of the resin flowing in the mold, it is necessary to solve by combining the above-mentioned viscosity prediction method and the basic equations of various conservation laws. Shown in

Equations (17), (18), and (19) are continuous equations, momentum, and energy conservation equations, respectively. In equations (17) to (19),
Q: flow rate, R: circular pipe radius, υ _Z : pipe axial velocity, γ: pipe radial distance, Z: pipe axial distance, P: pressure, η: viscosity, P: density, T:
Temperature, t: time, λ: thermal conductivity. The equations (17) to (19) are combined with the isothermal viscosity equations (1) to (4) and the non-isothermal viscosity prediction methods (7) to (16) to calculate the difference under the given initial conditions and boundary conditions. Solving with a numerical analysis method such as the finite element method enables a flow simulation in a circular pipe flow path.
FIG. 4 shows an outline of the simulation program used in this embodiment. In the output, the value of the average apparent viscosity when the Newtonian fluid is assumed to be in a steady isothermal laminar flow is also obtained.

Table 1 shows the physical property values of the epoxy resin for semiconductor encapsulation used in this example.

Here, p, c, and λ are values obtained using a commercially available thermophysical property measuring device. A, b, d, e, f, g are (2), (3), (4)
These are the parameters in the formula, these values are obtained by combining several types of circular pipe channels with different diameters and several types of mold temperature conditions,
The average apparent viscosity of the resin under each condition was actually measured, and determined based on these characteristic values by an extrapolation method, a curve fitting method, or the like. The physical property values shown in Table 1 were input to the simulation program shown in FIG. 3, and the calculated value when the average apparent viscosity ηa in the circular pipe flow path was calculated was compared with the actually measured value in FIG.
Shown in the figure. At each mold temperature, the two agreed very well, and the validity of the simulation method was verified.

6-a to 6-d show the outline of the manufacturing process of the resin-encapsulated semiconductor. FIG. 6A shows an enlarged view of a state in which chips 2 are mounted on a lead frame 1 and these are connected by gold wires 3, and a multiple lead frame 1 in which a plurality of such devices are mounted. FIG. 6-b shows a process of sealing the device with resin. First, the lead frame 1 is placed on the cavity 5 of the lower mold 4, and the upper mold 6 is closed and fixed in the mold. On the other hand, the thermosetting resin 7 preformed in the form of a tablet is preheated by a high frequency preheater (not shown) and then put into a pot 8, and the plunger 9 attached to the molding machine (not shown) is removed. Lower it. At this time, the resin 7 that has received heat from the mold heated by the heater 10 melts and flows into the cavity 5 through the runner 11 and the gate 12. After a predetermined time elapses after the cavity 7 is completely filled with the resin 7, the resin 7 is cured and taken out of the mold in the state shown in FIG. 6-c. Then, through the cutting and bending steps of the lead frame 1, the final shape shown in FIG. 6-d is completed. 6B, when the filling time of the resin 7 into each cavity 5 is shifted, the viscosity of the resin, the flow velocity,
The cured state is different, and there is a problem that the void remains, the gold wire 3 is deformed, and the like based on these factors. Therefore, a flow path design method for making the filling state of the resin 7 uniform will now be described.

In order to make the filling state of the resin into each cavity uniform, the mold flow path specifications that can equalize the sum of the pressure loss at the runner and the gate part until reaching each cavity when distributing the same flow rate to each cavity Just ask. Therefore, a calculation for estimating the pressure loss in the flow path is required.
The cross-sectional shape of the runner 11 and the gate 12 in FIG. b is a semicircular bottom or inverted trapezoid, and in most cases, the cross-sectional area changes along the flow direction. The calculation time required to perform the flow simulation in advance with such complicated boundary conditions becomes enormous, and it is not a practical design system. Therefore, the present invention uses the following method. That is, the flow path is divided into a plurality of sections, the flow path-specific shape resistance β and the flow rate Q are calculated in each section, and each section is replaced with a circular pipe shape, and a flow simulation is performed using this shape, and the resin , The temperature, the viscosity, the flow velocity, and the average apparent viscosity a were calculated, and the pressure loss ΔP was determined by the following equation.

ΔP = aQ (20) FIG. 7-a shows an example of one section of the flow path whose cross-sectional area changes along the flow direction. X is the distance along the flow direction from the reference point, and X ₁ and X ₂ are the start point and end point of the section, respectively. W is the width of the flow channel, h is the depth of the flow channel, and both are functions of X. Now, in this section, if W ≧ h, β
Is obtained by the following equation.

Here, F is a shape factor determined by the flow path cross-sectional shape and the ratio of W to h. In equation (21), β is obtained by giving W, h, F in the form of a function of X, and performing analytical or approximate integration by Simpson's formula or the like. In the condition of W <h, Is used. Further, a portion satisfying W ≧ h in the section and W <h
When there are coexisting locations, (2
What is necessary is just to add up using Formulas 1) and (22). 7-b
The figure shows the replaced circular channel. In the section X ₁ to X _2,
A circular pipe with a uniform pipe diameter. This diameter is determined by calculation so that the section volume in FIG. 7-a is the same as the section volume in FIG. 7-b. The broken line of the 7-b diagram shows the shape after replacement of the circular tube before and after the section of the section X ₁ to X ₂ in the flow path of the tapered along the flow direction. Since the replacement is performed in this manner, the flow simulation method in a circular pipe described above can be used as it is, and the average apparent viscosity a in each section can be estimated. In addition, the section passing flow rate Q is first determined from the mold channel volume V _f and the resin injection time tp of the plunger.
The flow rate Qp discharged from the pot is calculated in advance by Qp = _Vf / tp, and is obtained in advance by distributing Qp according to the number of branches of the flow path. As described above, the pressure loss in each section is obtained, and the accumulated pressure loss is obtained to obtain the total pressure loss ΔP _T.

FIG. 8 is a flow chart for designing runners and gates for adjusting the resin filling state in each cavity in the multi-cavity mold having the structure shown in FIG. 6-b. First, a resin physical property value, molding conditions, and mold data are input. Among these, the resin physical property values are physical quantities for each resin indicated by the symbols in Table 1. The molding conditions are the resin injection time of the plunger tp,
Maximum setting of the molding machine plunger pressure P _M, the resin preheating temperature,
Mold temperature. For the specifications of the mold, for the first calculation, provisional values are input for the specifications other than the fixed factors such as the pitch between cavities and the flow path layout. Next, the volume _Vf of the entire channel is calculated, and the channel is divided into sections.
At this time, the number of junction surfaces in the section is at least equal to the number of branches in the flow path, and there is no branch in the resin flow in the section. Then, the section volume Vn and the section shape resistance βn are calculated. From the above, first, the flow rate Qp discharged from the pot is defined as Qp
= _Vf / tp, and Qp is distributed according to the number of branches in the flow path to obtain the flow rate Qn in each section. At this time, it is assumed that the same flow rate is distributed to each cavity. Then, the resin passage time tn of each section is obtained from Vn / Qn. Further, the diameter of the circular pipe flow path having the same volume is obtained for each section from Vn. The flow simulation in the circular pipe channel replaced in this manner is sequentially performed from the upstream side under the given initial and boundary conditions, and the resin temperature, viscosity η, flow velocity distribution, and average apparent viscosity ηa in each section. Is calculated. Here, at a predetermined position in the radial direction of each section, η on the downstream side and that on the upstream side are compared, and it is checked that the downstream side does not rise above the upstream side. If an increase in η occurs on the downstream side, recalculation is performed by changing the molding conditions and mold specifications. This is because the condition under which the rise of η occurs during the flow is because the high-viscosity resin whose curing reaction has advanced flows into the cavity, and the possibility of molding failure is extremely high, and the purpose is to prevent this in advance. is there. When a condition without an increase in η is obtained,
First, the pressure loss ΔP _{Rn of} each section of the runner is calculated as ΔP _Rn = βn ·
Calculate with anQn, accumulate this and pressure loss ΔP in the runner
_Ask for _RT . Next, the pressure loss ΔP _R s ≦ ΔP _RT in the runner set in advance for comparison is compared, and when ΔP _RS ≦ ΔP _RT , the mold flow path, specifications, resin injection time of the plunger, resin preheating Change the value of at least one of the temperature and mold temperature and re-enter to find the ΔP _RT at that time, change the conditions sequentially, and change the runner specifications and molding conditions where ΔP _RS > ΔP _RT is satisfied. decide. This is because if the pressure loss approaches the set plunger maximum pressure P _M of the molding machine, the plunger can no longer be moved down at constant speed, the retention of the resin in the middle flow, there is a phenomenon that frequently molding defects, first runner this The purpose is to prevent in some parts. It should be noted, ΔP _RS will keep the much lower value than the P _M. Subsequently, the pressure loss at each gate portion is set so that the sum of the pressure loss at the runner portion and the pressure loss at the gate portion until reaching each cavity is constant.
At this time, the preset pressure loss ΔPs is compared with the total pressure loss ΔP _T obtained by calculation, and when ΔPs ≦ ΔP _T , re-calculation is performed by changing molding conditions and part of the mold flow path parameters again. .
Then, upon reaching the ΔPs> ΔP _T, to determine the pressure loss [Delta] P _G n should be given to the gate portion. ΔPs is ΔP _R s
To an intermediate value of P _M. Then, [Delta] P _G n and the flow gate portion average apparent viscosity was determined by simulation a _G; · and the shape resistance beta _G n should be given at each gate from the gate unit flow rate _{Q G n β G n = ΔP} G n / a G Calculated by Q _G n.
Then, using the relational expressions shown in Expressions (21) and (22),
Inversely calculates the specifications of the gate. Further, if the obtained specifications do not satisfy the constraints at the gate portion, such as the upper and lower limits of the angle of the tapered portion along the flow direction, the upper and lower limits of the depth, etc. A part of the condition is changed, and gate specifications are determined where the constraint condition is satisfied.

9-a to 9-c show the structures of the mold runner 11 and the gate 12 designed using this method. FIG. 9-a shows the structure of the runner 11 and the gate 12 when FIG. 6-b is viewed from above. Here, in FIG. 15-b, the pot 8 and the runner 11 and the cavity 5 up to the bent portion connected to the pot are omitted. FIG. 9-b is a side view of FIG. 9-a, and the runner 11 has a structure in which the depth is gradually reduced along the flow direction in order to reduce the deviation of the arrival time of the resin to each cavity. . FIG. 9-c is a view of FIG.
FIG. 4B is a diagram showing a cross section taken along the line AA and a cross section taken along the line BB of FIG. Structured. If there is a constraint on the gate throttle angle, the width and depth of the gate outlet 13 may be changed to secure the necessary pressure loss value at each gate.

Next, the effects of the present invention will be described. FIGS. 10-a and b show the inside of the cavity by the conventional method in which the mold having the structure of 9-a, b and c was designed on the assumption that the viscosity of the resin was constant without using the flow simulation method. It shows the filling state of the resin. The vertical axis in FIG. 10-a shows the dimensionless filling rate of the resin in each cavity, and the horizontal axis shows the dimensionless filling time since the resin started to enter the cavity. Shows the ideal filling at the same speed.
In the conventional method, the filling of each cavity with the resin greatly deviates from the ideal filling. FIG. 10-b shows the state of filling of the resin 7 at the dimensionless filling time 0.5 in FIG. 9-a, in which the resin is rapidly filled from the cavity 5 on the upstream side. FIG. 11-a shows the filling state of the resin in the cavity in the mold designed according to the present invention using the flow simulation method. Filling conditions very close to ideal filling were obtained in all cavities. FIG.
FIG. 3A shows the state of filling of the resin 7 at the dimensionless filling time 0.5 in FIG.

FIG. 12 shows a comparison between the resin maximum flow velocity in the cavity and the resin residence time. Here, tp indicates the resin injection time. In the mold designed by the conventional method, the flow velocity becomes higher in the cavity on the downstream side. This indicates a result that the flow rate shifts to the downstream every time the resin is completely filled from the upstream side due to the filling state shown in FIGS. 10-a and 10-b. On the other hand, in the mold designed by the present invention, as shown in FIGS. 11A and 11B, the resin is uniformly filled, so that the flow rate concentration does not occur, and the flow velocity shows almost the same value as each cavity. On the other hand, in the mold designed by the conventional method, the residence time of the resin increases in the cavity on the upstream side. Here, the residence time is the time from completion of filling of the resin in the cavity to stop of the plunger. In the mold designed by the present invention, there is almost no residence time in any cavity.

FIG. 13 shows a comparison of the incidence rate of defective gold wire deformation. Here, the results when two types of the gold wire A having a large diameter and the gold wire B having a small diameter are used are shown. In the case of the metal wire A, there is no metal wire deformation defect in the metal mold designed by the conventional method or the metal mold designed by the method of the present invention. On the other hand, in the case of the gold wire B, in the mold designed by the conventional method, the defect generation rate becomes higher toward the cavity on the downstream side. This corresponds to the increase in the flow velocity in FIG. 12, and indicates that the gold wire having a small diameter and a small rigidity tends to be deformed as the flow velocity increases. On the other hand, in the mold designed by the method of the present invention, there is no increase in the flow velocity, so that no defect occurs even in the wire B.

 Table 2 shows a comparison of the occurrence rate of appearance defects of molded products.

Under the condition that tp was 18 s, no defect occurred in either method, but when tp reached 30 s, the defect rate of the mold calculated by the conventional method was 100%. This is the eleventh
This is because the residence time of the gate shown in the figure becomes very long, and the resin hardens without sufficiently applying pressure in the cavity. On the other hand, in the mold according to the present invention having almost no gate stagnation, no defect occurs even under this condition.

〔The invention's effect〕

According to the present invention, the design of the optimal flow path specifications and the selection of the optimal molding conditions for mass-produced dies can be performed quickly and with high precision on a desk. The effect of reducing costs and reducing costs by reducing the diameter of the gold wire is very large.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of the analysis system of the present invention, FIG. 2 is a characteristic diagram of an isothermal viscosity model used in one embodiment of the present invention, and FIG.
The figure is an explanatory diagram for calculating the change in viscosity in a non-isothermal state,
FIG. 4 is a schematic flowchart of a flow simulation,
FIG. 5 is a comparison diagram of the measured value of apparent viscosity a and the calculated value,
FIGS. 6-a to 6-d are explanatory views of the resin sealing process of the semiconductor, FIGS. 7-a to 7-b are explanatory views for calculating the pressure loss in the flow path, and FIG. Flowchart for runner and gate design of casting die, 9-a to 9-c
The figure shows the mold runner and gate structure, 10-a, 10-
Fig. b is a diagram showing the state of resin filling in the cavity by the conventional method, Figs. 11-a and 11-b are diagrams showing the state of resin filling in the cavity by the method of the present invention, and Fig. 12 is a resin in the cavity. Fig. 13 is a comparison diagram of the maximum flow velocity and the resin residence time, and Fig. 13 is a comparison diagram of the occurrence rate of defective gold wire deformation. 4 ... lower mold, 5 ... cavity, 6 ... upper mold, 7 ... thermosetting resin, 8 ... pot, 11 ... runner, 12 ... gate.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuhiro Sugino 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. Production Research Laboratory (72) Inventor Kunihiko Nishi 5--20, Josuihoncho, Kodaira-shi, Tokyo No. 1 Inside the Musashi Plant of Hitachi, Ltd. (56) References JP-A-59-88656 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 11/00-11/04

Claims (4)

(57) [Claims] In the design of a mold provided with a pot and a flow path connected to the pot, a flow path volume V _f
Is calculated, setting the resin injection time t _p of the plunger for injecting a thermosetting resin was charged into the pot in the flow passage, the resin flow rate Q _p is injected from the pot into the flow path Q _p = _Vf
/ t _p , and distributes Q _p according to the number of branches of the flow path, calculates the flow rate Q _n at an arbitrary position in the flow path, and moves the flow path in the flow direction of the resin. Divide into a plurality of sections at any vertical cross section, and in each section, calculate the flow path resistance value β _n determined from the flow path width, depth, cross-sectional shape and length, and set each section in the flow direction. Along with the shape of a circular pipe, solve the basic equation describing the viscosity change transport phenomenon of the resin under the given initial and boundary conditions in the circular pipe, and calculate the average apparent viscosity _an of the resin in each part of the circular pipe And
The pressure loss [Delta] P _n occurring in each section calculated in _{ΔP n = β n an Q n} , the pressure loss prediction method in the mold, characterized in that determining the total pressure loss [Delta] P _T by accumulating [Delta] P _n. 2. The method of claim 1, wherein, when comparing the overall pressure drop [Delta] P _T determined by calculation the pressure loss [Delta] P _S set in advance for comparison, was a ΔP _S ≦ ΔP _T, the flow path Of the specifications, the injection time of the plunger, the temperature of the mold, and the preheating temperature of the resin, at least one of the conditions is changed and the value is re-input to obtain ΔP _T at that time, and the conditions are sequentially changed to obtain ΔP _S > A mold flow path design method characterized in that flow path specifications and molding conditions are determined within a range satisfying> ΔP _T. 3. The method according to claim 2, wherein the resin viscosity on the downstream side is higher than that on the upstream side at a predetermined position in the radial direction within the circular pipe replaced in each section, satisfying ΔP _S > ΔP _T. A flow path design method for a mold, characterized in that flow path specifications and molding conditions are determined within a range not satisfying the requirement. 4. The mold according to claim 1, wherein the mold has a structure in which a plurality of cavities branched and connected via a gate to a runner connected to the pot are arranged along the runner. The number should be at least the same as the number of branches in the channel,
Assuming that the same flow rate is distributed to each cavity,
A method of designing a mold flow path, comprising changing gate specifications for each of the cavities so that the total pressure loss in the runner and the gate is constant for each of the cavities.