JP7644129B2 - Manufacturing method for double-sided cooled power module - Google Patents

Description

The present invention relates to a dual side cooling (DSC) power module for a power semiconductor package, and more particularly to a manufacturing method for controlling the thickness of a package having members stacked therein and the module.

In the current power semiconductor market, high-end power modules that use high voltage and high current require more efficient heat dissipation. In particular, double-sided cooling power modules for power semiconductor packages require higher thermal performance in response to the high operating temperatures of semiconductor chips due to high power density and high speed.

For example, Patent Document 1 discloses a double-sided cooled power module that is composed of a lower end terminal, a power semiconductor chip, a horizontal spacer, an upper end terminal, and a vertical spacer, and in which these components are stacked inside.

U.S. Patent No. 9,390,996B2

When stacking components using conventional methods, a dry process is carried out using a printed bonding material (adhesive) before the die mounting process. However, because the surface of the printed bonding material is not uniform in flatness, there is a concern that chip cracks or cracks may occur in the insulating substrate in the next process.

In addition, because there is variation in the thickness of the stacked materials, it is difficult to keep the overall layer thickness constant when stacking them one by one using the conventional method that does not involve a bonding material drying process.

When the material thickness tolerance directly affects the thickness tolerance of the entire module, in order to control the stacking height of the double-sided cooling module, after the dies and other parts are stacked and attached to the opposing insulating substrates, the bonding material (adhesive) that is finally attached to the substrate is used as a buffer bonding layer (buffer adhesive layer) using a special metal jig and a reflow process without pre-drying.

The final bonding layer, which does not involve a dry process, can use a special metal jig to compensate for all thickness variations in the raw materials and laminated materials as a buffer bonding layer, which allows the stack height (H) variation of the power semiconductor double-sided cooling (dual-sided cooling module) to be smaller than before.

Furthermore, power semiconductors can be optimized for thermal performance to suit water jacket cooling systems, which means cheaper materials (materials with relaxed dimensional tolerances) can be used and the package thickness of the power semiconductors can be made uniform.

1A and 1B are diagrams illustrating a method for manufacturing a double-sided cooled power module according to a first embodiment of the present invention; 3A and 3B are diagrams illustrating a method for manufacturing a double-sided cooled power module according to the first embodiment of the present invention. 1 is a schematic cross-sectional view of a double-sided cooled power module according to a first embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description in any way.

The manufacturing method of the double-sided cooling power module according to the first embodiment of the present invention is explained with reference to Fig. 1. Fig. 1 (1)-(2) and Fig. 2 (3)-(4) are schematic cross-sectional views showing the manufacturing process, i.e., the assembly process flow for constructing the buffer adhesive layer.

1(1) shows a first bonding process in which a first bonding material 5 is bonded onto a first substrate 1 and pre-dried, and then an electronic component is mounted and bonded. Here, the electronic component is a die 4 bonded onto a spacer 3 using a third bonding material 6.

The first substrate 1 can be an insulating substrate, for example, a DBC substrate or a TPC substrate with a circuit pattern arranged on one side. The spacer 3 is a conductive metal plate and can be Cu. The die 4 is a semiconductor chip and can be Si, SiC, or GaN.

The first bonding material 5 and the third bonding material 6 are similar sintered materials. In bonding using a sintered material, the sintered material is usually applied, pre-dried, and then pressurized and heated to bond the objects to be bonded. Pre-drying also keeps the shape of the bonding material flat.

1 (2) shows a second bonding process in which a second bonding material 7 is bonded onto a second substrate 2. Here, the second substrate 2 can be an insulating substrate similar to the first substrate 1. The second bonding material 7 is a sintered material similar to the first bonding material 5 and the third bonding material 6, and can be manufactured by printing a paste-like material and applying it to the substrate, without using a pre-drying process.

FIG. 1(3) shows a third bonding process in which the electronic components (spacer 3 and die 4) bonded to the first substrate 1 and the second bonding material 7 bonded to the second substrate 2 are bonded face to face.

Each bonding material becomes a sintered bond layer, but the first bonding material 5 and the third bonding material 6 are pre-dried, so they harden and can maintain a flat shape. The second bonding material 7 is not pre-dried, so it maintains a softened state.

1(4), the substrates formed in the third bonding process are placed in a lower reflow jig 8, and then covered with an upper reflow jig 9. A special metal jig 10 is used to apply tension from the inside between the first substrate 1 and the second substrate 2. Then, in the fourth bonding process, the substrates are heated and bonded.

Fig. 3 shows the state after removal from the reflow jig after the fourth bonding step described above. Usually, the double-sided cooling power module is completed by molding the space between the boards with a molded resin. Here, the molded resin and the external lead-out terminals are the same as those seen in the prior art, and are therefore not shown.

Here, when the second bonding material 7 is bonded in a softened state, it is crushed into a fillet shape and becomes a buffer bonding layer (buffer adhesive layer).

In other words, by using a softened adhesive layer that has not been pre-dried as a buffer, the second bonding material 7 can absorb the dimensions as a buffer and maintain the target module thickness H (Figure 3) even if there is a large variation in the thickness of the spacer 3 or die 4.

Even when there are a plurality of spacers or dies, the stacking height can be corrected. This also applies when the stacking order of the spacers or dies is arbitrary.

Resin decomposition and cross-sectional analysis of the completed double-sided cooled power module confirmed that the fillet shape was different from the laminated structure of other power semiconductor modules.

Conventional reflow jigs are called location guide blocks and have a structure in which the power module is sandwiched between upper and lower jigs. Therefore, although the maximum height of the power module can be controlled, it is difficult to control the minimum height.

Therefore, in the present invention, the special metal jig 10 is used by combining the lower reflow jig 8 and the upper reflow jig 9, inserting the special metal jig 10 into the inside of each board so as to press the board against the inner walls of the lower reflow jig 8 and the upper reflow jig 9 from the inside of the board, and applying tension, and by using the second bonding material 7, which is the last flowable adhesive layer under the die 4, as a buffer bonding layer (buffer adhesive layer), the stack thickness H can be corrected to control it to a constant height.

If the double-sided cooled power module can be controlled to a constant height, it will not be affected by variations in the thickness of the laminated components, and when it is incorporated into a unit or device, there will be no gaps between it and the heat sink (water jacket), and sufficient contact will be achieved, allowing high thermal performance to be maintained.

The number of electronic components may be one or more, and the combination of the spacers 3 and the dies 4 and the order of stacking may be freely changed.

The second bonding material may be disposed between the "substrate and die", the "die and spacer", or the "spacer and substrate", with the same effect.

Moreover, the spacer may be made of Cu, Cu/Mo, or the like.

Furthermore, if the thickness variation is corrected, the bonding material before pre-drying can be of tape or paste type.

1, first substrate 2, second substrate 3, spacer 4, die (chip)
5: First bonding material 6: Third bonding material 7: Second bonding material (buffer bonding layer)
8, lower reflow jig 9, upper reflow jig 10, special metal jig 11, power module

Claims (4)

A method for manufacturing a double-sided cooled power module, comprising a first bonding process in which a first bonding material is bonded onto a first substrate and pre-dried, followed by mounting and bonding of electronic components; a second bonding process in which a second bonding material is bonded onto a second substrate; a third bonding process in which the electronic components bonded to the first substrate and the second bonding material bonded to the second substrate are bonded face-to-face; and a fourth bonding process in which tension is applied between the first substrate and the second substrate, and the substrates are heated and bonded. The method for manufacturing a double-sided cooled power module according to claim 1, characterized in that the first bonding material or the second bonding material is a sintered material, contains at least one of silver, copper, silver oxide, and copper oxide, and is in a paste or tape state. The method for manufacturing a double-sided cooled power module according to claims 1 and 2, characterized in that the electronic components are made of semiconductor chips, spacers, or a combination thereof, Si, SiC, or GaN. The method for manufacturing a double-sided cooled power module according to any one of claims 1 to 3, characterized in that the first substrate and the second substrate are made of DBC (Direct Bonded Copper) substrates.

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