JP3139482B2 - Mold package before mounting and method for correcting warpage thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold package before mounting and a method for correcting warpage thereof, and more particularly to a mold package before mounting for correcting warpage of a thin and large mold package and a method for correcting warpage thereof.

[0002]

2. Description of the Related Art A mold package is soldered at the time of mounting. Warpage occurs in the mold package due to thermal stress during soldering. The mold package that was convex before mounting changes to concave after mounting due to the thermal stress. Here, the convex shape is a geometric form of the mold package defined from the viewpoint of the printed circuit board to be mounted.

[0003] Such a change in form causes defective soldering mounting. Techniques for preventing the occurrence of such defects are described in JP-A-64-57630 and JP-A-8-16248.
No. 6 is known. These known techniques are techniques for suppressing the occurrence of warpage by applying heat to a mold package that is supposed to cause warpage and cooling while compressing the mold package from both sides. This is a diversion of a kind of annealing technique. Such annealing is not a technique for guaranteeing that warpage during mounting is completely prevented.

[0004] It is desired to minimize the occurrence of defects during mounting without causing thermal deformation during mounting. It is preferable to incorporate a step that does not cause thermal deformation during mounting into the assembly process of the mold package, and it is further desirable that the efficiency of the step be high and the manufacturing equipment be inexpensive.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a mold package before mounting and a method for correcting warpage of the package before mounting, which does not cause thermal deformation during mounting and minimizes the occurrence of defects during mounting. . Another subject of the present invention is:
An object of the present invention is to provide a mold package before mounting and a method for correcting warpage thereof, which has a high efficiency of steps for preventing thermal deformation during mounting. Still another object of the present invention is to provide a mold package before mounting and a method for correcting warpage thereof, in which manufacturing equipment for steps that do not cause thermal deformation during mounting is inexpensive.

[0006]

Means for solving the problem are indicated in the following description in which the means for solving the problem are expressed according to the claims. It shows that it corresponds to the member, the process, and the operation of at least one of a plurality of forms of the present invention. However, the solution means of the present invention is to be interpreted as being limited to the members of the embodiment indicated by those numerals. It is not a thing, but to clarify the correspondence.

The method for correcting the warpage of a mold package before mounting according to the present invention is directed to a mold package (11, 12) having a two-layer structure and warping in the direction of the normal to the thermal interface of the two-layer structure. ) Is a method for forming a warped shape of a mold package for positively imparting the warped shape, wherein the two-layer structure is provided for a first temperature applied to a first layer (1) which is one of the two-layer structures. And the step of relatively controlling the second temperature applied to the second layer (2), which is the other layer.

By positively applying a temperature difference to the first layer (1) and the second layer (2) before mounting, it is possible to avoid the occurrence of warpage during the soldering step. In a two-layer structure object in which warpage has occurred to some extent, the warp is not substantially further amplified by the second temperature difference. This step is preferably included in the assembly process of the mold package (11). It is particularly important in terms of complanability that the step is inserted before the lead forming step involved in the assembly process.

The step includes the step of providing a thermal head between the first temperature and the second temperature. Even if there is no temperature drop, when the first layer (1) and the second layer (2) have different expansion coefficients, warpage in a specified direction can be given.
It is preferable to lower the first temperature below the glass transition point of the first layer (1) and maintain the second temperature above the glass transition point of the second layer (2). In that case, it is particularly important that the descent is quenching. Means for positively shortening the time for lowering the first layer below the glass transition point is actively used.

The holding of the holding step is preferably performed on a board (4) or a hot plate, and the lowering of the lowering step is preferably performed by an air blow (6), from the viewpoint of reducing equipment costs. It is practically desirable to correct the warpage from the convex shape defined during mounting to the concave shape defined during mounting.

The mold package before mounting according to the present invention is provided with a concave warpage defined after mounting.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Corresponding to the drawings, the embodiment of the method for correcting warpage of a mold package before mounting according to the present invention is provided with a thermal deformation process. As shown in FIG. 1, the mold package 11 is formed of a resin-molded upper package 1 and a resin-molded lower package 2. The upper package 1 and the lower package 2 have a two-layer structure thermally. In the vicinity of the height position of the boundary surface of the two-layer structure, many lead wires 3 are arranged so as to protrude from the molded resin molded body.

The arrow shown in FIG.
1 shows the expansion direction when the temperature rises substantially uniformly as a whole. The temperatures are both higher than the glass transition point. The upper package 1 is heated to a temperature higher than its glass transition point (hereinafter, referred to as a first glass transition point), and the lower package 2 is heated to a temperature higher than its glass transition point (hereinafter, referred to as a second glass transition point). I have. Although the arrows are absolutely shown, warpage can be shown as relative expansion and contraction directions (expansion and contraction directions).

FIG. 2 shows that the temperature of the lower package 2 is maintained at or above the second glass transition point, and the temperature of the upper package 1 is maintained at the first glass transition point.
It shows the directions of expansion and contraction of both layers 1 and 2 when the temperature falls below the glass transition point. The upper package 1 is contracting, and the lower package 2 is expanding. When the temperatures of both layers are both equal to or higher than the glass transition point and there is a difference between the two temperatures, the expansion and contraction thereof can be relative.

FIG. 3 shows a mold package before mounting and a warpage of the mold package 12 formed by the warp correcting method according to the present invention, which is before mounting.
The mold package 12 shown in FIG. 3 is obtained through the thermal history of the process including the steps shown in FIG. 1 and the steps shown in FIG. Since the extension amount (positive) of the lower package 2 is larger than the extension amount (either positive or negative) of the upper package 1, the radius of curvature of the upper surface of the upper package 1 is smaller than the radius of curvature of the lower surface of the lower package 2. . When a mounting target such as a printed wiring board is arranged on the lower side of the lower package 2 or on the side of the lower package 2, the mold package 12 shown in FIG. 3 is defined to be concave.

The step of lowering the temperature of the upper package 1 to a temperature equal to or lower than the first glass transition point while maintaining the temperature of the lower package 2 equal to or higher than the second glass transition point is that the temperature drop is rapid cooling. Is preferred. When the rapid cooling is performed in this manner, when the lower package 2 is in the expanded state, the upper package 1 contracts and hardens, and the lower package 2 expands due to the concave warpage of the upper package 1 that contracts and hardens. It will imitate the warpage of 1. Such copying is more effective for quenching.

FIG. 4 shows such a rapid cooling method. The mold package 11 is placed on the upper surface of the board 4. By heating the board 4, the lower package 2
Is raised to a temperature equal to or higher than the second glass transition point and maintained at that temperature. Due to the propagation of the temperature, the temperature of the upper package 1 also rises to a temperature equal to or higher than the first glass transition point. The entire board 4 and the mold package 11 may be heated.

The heating is stopped, and a cooling gas is blown from the air blow 6 onto the upper surface of the upper package 1. The lower package 2 which is in contact with the board 4 and is shielded from the airflow of the air blow 6 by the upper package 1 has poor heat radiation.
The upper package 1 that comes into direct contact with the cooling airflow has good heat dissipation. Due to such a difference in heat radiation, a temperature difference between the upper package 1 and the lower package 2 is suddenly generated. Due to this temperature drop, a concave warpage is positively applied to the mold package 11 so that the mold package 12 can be formed.

By using the board 4, the temperature of the mold package 11 can be raised by using a heating means such as an infrared reflow furnace, a thermostat, or a hot plate. A temperature difference can be created. It is preferable that the air blow 6 be capable of uniformly cooling the surface of the upper package 1.

Example: A mold package 11 is placed on a SUS board 4, and the board 4 is heated on a hot plate and cooled by air blow, while maintaining the temperature of the lower package 2 at or above its glass transition point. Upper package 1
The time required to lower the temperature of the
When the cooling time was 20 seconds, no concave change was observed, as compared to the case where the displacement of the warp around the mold package 12 was 80 microns. According to this comparative test, under certain experimental conditions,
8 seconds can be defined as rapid cooling and 20 seconds as slow cooling.

From the experiments according to this embodiment, it is necessary to control the cooling time in order to rapidly cool one while maintaining the other at or above the glass transition point while maintaining one at or above the glass transition point. The mold package before mounting and the warpage correcting method according to the present invention include some means for positively controlling the quenching time. Such means can be provided in various ways, for example, controlling the temperature of the cooling gas of the air blow 6, controlling the flow rate thereof, and controlling the temperature after the entire heating.

It is important that the warp correcting step in the entire process of assembling the mold package is inserted before lead molding so that coplanarity is not affected during mounting.

[0023]

According to the present invention, the mold package before mounting and the method for correcting the warpage thereof can prevent the occurrence of defects due to soldering during mounting. The steps for this are simple and the equipment is inexpensive.

[Brief description of the drawings]

FIG. 1 is a sectional view showing steps of an embodiment of a method for correcting a warpage of a mold package before mounting according to the present invention.

FIG. 2 is a cross-sectional view showing another step thereof.

FIG. 3 is a sectional view showing still another step thereof.

FIG. 4 is a sectional view showing still another step thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st layer (upper package) 2 ... 2nd layer (lower package) 3 ... Lead wire 4 ... Board or hot plate 6 ... Air blow 11, 12 ... Mold package

Claims (9)

(57) [Claims] 1. A warp shape of a mold package for positively imparting a warp shape of a mold package having a two-layer structure thermally and warping in a direction of a normal to a thermal boundary surface of the two-layer structure. A second temperature applied to a second layer, which is another layer of the two-layer structure, relative to a first temperature applied to a first layer, which is one layer of the two-layer structure. To correct the warpage of the mold package before mounting. 2. The method according to claim 1, wherein the step is included in an assembly process of the mold package. 3. The method according to claim 2, wherein the step is inserted before a lead forming step included in the assembling process. 4. The warpage correction of a mold package before mounting according to claim 2, wherein the step includes a step of giving a thermal head between the first temperature and the second temperature. Method. 5. The method according to claim 2, wherein the step of lowering the first temperature is lower than the glass transition point of the first layer, and the step of lowering the second temperature of the second layer. A method for correcting warpage of a mold package before mounting, comprising a holding step for holding the above. 6. The mold package according to claim 5, wherein the step of lowering includes a step of positively shortening a time for lowering the first layer below the glass transition point. How to correct warpage. 7. The method according to claim 5, wherein the holding in the holding step is performed on a hot plate, and the lowering in the lowering step is performed by air blowing. 8. The method according to claim 1, wherein the step includes correcting the warpage from a convex shape defined at the time of mounting to a concave shape defined at the time of mounting. To correct the warpage of the mold package. 9. A mold package before mounting having a thermally two-layer structure and having a concave warpage defined after mounting.