JP3419642B2 - Power module - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power module that requires high reliability and heat dissipation when mounting an electronic component such as a semiconductor chip having a high heat generating property.

[0002]

2. Description of the Related Art Alumina (Al ₂ O ₃ ) and aluminum nitride (Al
N), beryllium oxide (BeO), and other ceramics sintered bodies are used as substrates, and circuit boards in which a circuit board made of copper (Cu) or the like is integrally bonded to the surface thereof as a conductive layer are widely used.

A circuit board using an alumina sintered body has a circuit board made of a metal such as Cu having excellent thermal conductivity and electrical conductivity, so that the circuit operation is delayed little and the circuit wiring has a long life. For a long time, it has good wettability with a bonding material such as solder, and can bond a semiconductor chip (IC element) or an electrode plate to the surface of a ceramic sintered body with high bonding strength. As a result, the heat generated from the semiconductor chip It is possible to maintain good radiation performance and semiconductor chip operation reliability.
Further, by bonding a metal plate such as Cu to the back surface of the ceramic substrate, there is an advantage that the purpose of stress relaxation and thermal deformation prevention of the ceramic substrate can be achieved.

However, the distance between the end of the semiconductor chip and the end of the metal circuit is often as small as 1 to 2 mm, and if the thermal conductivity of the ceramic substrate is small, the heat dissipation becomes insufficient, resulting in a thermal resistance. Since the size of the semiconductor chip becomes large, there is a problem that it cannot cope with the high output of the semiconductor chip.

For the above reasons, it has attracted attention to use a ceramic sintered body having a high thermal conductivity for the substrate, and it is possible to improve the thermal conductivity of an aluminum nitride sintered body or a conventional ceramic sintered body such as alumina. It is planned. In a ceramic substrate such as aluminum nitride, if it is attempted to increase the thermal conductivity in order to obtain high heat dissipation, it is necessary to reduce impurities in the ceramic substrate, reduce grain boundaries, and increase the size of crystal grains. However, if the crystal grain boundaries are reduced and the crystal grains are increased, there is a problem in that the strength of the ceramic substrate decreases.

In particular, in an aluminum nitride circuit board using aluminum nitride as a ceramics board, in order to have sufficient durability against damage caused by thermal shock or heat history such as heat shock or heat cycle,
An example has been reported in which the thickness of the bonding layer interposed between the Cu circuit and the aluminum nitride substrate is increased to, for example, 20 μm or more (see Japanese Patent Laid-Open No. 6-196828). However, when the thickness of the bonding layer is increased, there are problems that it becomes difficult to remove an unnecessary brazing material in a later step and heat resistance increases.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation. The present inventors have conducted various studies to solve the above problems, and when a semiconductor chip and a metal circuit on a power module are placed in a specific arrangement relationship, a ceramic substrate having a thermal conductivity and a mechanical strength that are not so large. Even if it is used, it has sufficient durability against damage caused by heat shock and heat history such as heat shock and heat cycle, and has the same thermal resistance as when using a ceramic substrate with high thermal conductivity The present invention has been achieved based on the finding that a power module excellent in radiation performance can be obtained.

That is, the object of the present invention is to have sufficient durability against damage caused by heat shock or heat history such as heat shock or heat cycle, and also have excellent heat dissipation, and to prevent damage to the ceramic substrate. An object of the present invention is to provide a highly reliable power module in which insulation failure such as insulation breakdown is unlikely to occur.

[0009]

The present invention is a power module in which a metal circuit is provided on at least one main surface of a ceramic substrate, and a semiconductor chip is disposed on the metal circuit. When viewed from a direction perpendicular to the half-line L, a half-line L is drawn in an arbitrary direction from the center of gravity of the semiconductor chip, and the distance between the end of the semiconductor chip and the metal circuit end is D on the half-line L. The power module is characterized in that the semiconductor chip is arranged such that at least one half line satisfying D ≧ W exists when the distance from the center of gravity to the end is W.

A power module is preferably characterized in that the semiconductor chips are arranged so that two or more half lines satisfying D ≧ W are present, and more preferably D in all directions. In the power module, the semiconductor chips are arranged so that a half line of ≧ W exists.

Further, the present invention is a power module characterized in that the ceramic substrate is made of an aluminum nitride sintered body or a silicon nitride sintered body.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings. 1A and 1B are views showing an example of a power module of the present invention, FIG. 1A is a plan view, and FIG. 1B is a sectional view taken along the dotted line AA ′ in FIG. In the present invention,
Half line L drawn from the center of gravity G of the semiconductor chip in any direction
The distance between the end of the semiconductor chip and the end of the metal circuit is D,
When the distance from the center of gravity G of the semiconductor chip to the end of the semiconductor is W, it is important to arrange the semiconductor chip on the metal circuit so that at least one half line with D ≧ W exists. Therefore, according to the study by the present inventors, it is possible to obtain a power module that achieves the object of the present invention only when the above condition is satisfied.

The reason for this is not clear, but it is considered that when D is less than W, the flow of heat in the lateral direction of the metal circuit is suppressed, and the heat dissipation is deteriorated. Therefore, the greater the number of half-lines satisfying the above condition, the more the heat-dissipating effect is expected. However, according to the results of the study conducted by the inventors, the effect is remarkable with two or more lines, and D is effective in all directions. The heat radiation effect is expected most when the arrangement is such that there exists a half line of ≧ W, which is suitable for achieving the object of the present invention.
In particular, the above arrangement is effective when the semiconductor chip has a high output, and the heat generation amount of the semiconductor chip is 200 W.
It is especially effective when it exceeds.

In the case of a power module having a plurality of semiconductor chips mounted therein, the arrangement of the semiconductor chips exhibiting the largest heat generation on the metal circuit may satisfy the above conditions. It is only necessary to dispose so as to satisfy the above conditions, and it is more preferable to dispose so as to satisfy the above conditions for all semiconductor chips. In particular, when mounting two or more semiconductor chips that generate more than 200 W of heat, it is more desirable to satisfy the above arrangement structure for any of the chips.

When mounting a plurality of semiconductor chips on one metal circuit, in order to ensure sufficient heat dissipation of each semiconductor chip, the intervals between the semiconductor chips are, for example, two adjacent semiconductor chips. If the distances from the center of gravity of each chip to the edge of the semiconductor are Wa and Wb, respectively,
It may be arranged such that (Wa + Wb) or more. That is,
(Wa + Wb) may be replaced by the above D.

As the ceramic sintered body of the present invention, any material having excellent electrical insulation and heat resistance such as alumina, mullite, silicon nitride, aluminum nitride, and beryllium oxide may be used. There is no particular limitation. However, a material having a thermal conductivity of 60 W / mK or more is suitable for exhibiting a good heat dissipation property, and a ceramic fired body having a bending strength of 350 MPa or more is ensured in order to secure the strength after forming the circuit board. Consolidation is preferred.

Among these ceramics sintered bodies, the aluminum nitride sintered body has a high thermal conductivity and is therefore effective for use in a high output power module. The silicon nitride sintered body has a slightly low thermal conductivity, but has a high bending strength. It is effective because of its large size. In particular, since the silicon nitride sintered body has a smaller coefficient of thermal expansion than the ceramic sintered body such as the aluminum nitride sintered body, the power module obtained has high resistance to thermal shock and is further excellent in reliability. Is.

The joining layer of the present invention is generally formed by using a brazing paste. The brazing material paste is, for example, a metal circuit board or a metal radiator plate made of C
When it is u, it is a brazing material containing Ag or Ag and Cu, and preferably the brazing material containing an active metal such as Ti, Zr or Hf.

As a material for the metal circuit board and the metal heat dissipation plate formed on the ceramic substrate, a metal such as copper, nickel, aluminum, molybdenum, or tungsten, or an alloy containing the metal as a main component can be used.

An example of the method of manufacturing the power module of the present invention will be described. First, a brazing material paste containing Ag, Cu and Ti as an active metal is applied to the entire surface of a ceramics substrate (sintered body processed to have a maximum surface roughness of about 10 μm or less), and then spread sufficiently to cover the paste surface. A solid metal plate (Cu) is placed in contact. The ceramics substrate on which the solid metal plate is arranged is heat-treated to manufacture a joined body of both.

A circuit pattern is screen-printed on the metal plate of the bonded body thus manufactured by using an etching resist to form a resist circuit pattern. The circuit pattern structure at this time complies with claim 1 and / or 2.

Next, after etching processing to remove unnecessary metal and brazing material outside the pattern, the etching resist film is removed to obtain a ceramic circuit board having a metal circuit. Thereafter, in order to prevent oxidation and corrosion of the metal circuit, a protective film is selectively formed on the metal circuit by Ni plating or the like, if necessary.

Next, cream solder is applied to a heat sink provided with a solder resist, and the above-mentioned circuit board is placed and heated to bond them. Further, the semiconductor chip coated with cream solder is placed at a predetermined position, heat-treated and bonded, and then a lead wire is bonded to the semiconductor chip. Cream solder is applied to the electrodes of the resin case in which the electrodes are embedded, and the electrodes are covered with a heat sink and heat-treated for bonding. Finally, resin sealing is performed to obtain a power module.

The present invention will be described in more detail based on the following examples.

[0025]

【Example】

[Examples 1 to 4, Comparative Examples 1 and 2] Thermal conductivity 130 W / m
K, a thickness of 0.65 mm, and an aluminum nitride sintered body having a size of 50 × 60 mm, the active metal (Ti) -containing Ag—Cu-based brazing material paste was applied to both surfaces by a screen printing method, and was dried. A 3 mm Cu plate for metal circuits and a 0.15 mm thick Cu plate for metal heat dissipation are placed in contact with each other,
Heat treatment was performed in vacuum at 830 ° C. for 30 minutes to obtain a joined body of the aluminum nitride substrate and the Cu plate.

An ultraviolet-curable etching resist was printed on the Cu plate of the above-mentioned bonded body by a screen printing method and cured. The circuit pattern at this time is 24 ×
It was 42 mm, 32 × 42 mm or 24 × 30 mm. After that, with the ferric chloride solution, unnecessary C except for the pattern is added.
u was removed. Then, after removing the unnecessary brazing material between the Cu circuit patterns with an aqueous solution containing ammonium hydrogen fluoride and hydrogen peroxide, the resist was removed. Furthermore, electroless N
A Ni protective film was selectively formed at a predetermined position on the Cu circuit by i plating.

According to the above operation, the aluminum nitride circuit boards shown in Examples 1 and 2 of Table 1 and Comparative Example 1 were completed. For the samples of Examples 3 and 4 and Comparative Example 2, the ceramic substrate had a thermal conductivity of 70 W / mK and a thickness of 0.3.
A sample was obtained by the method described above except that a silicon nitride sintered body having a size of 5 mm and a size of 60 × 50 mm was used.

A transistor having a bottom area of 16 × 20 mm is mounted as a heat source on the center surface of the metal circuit of these circuit boards, and a Cu plate having a thickness of 2.5 mm is soldered on the back surface as a heat sink to manufacture a power module. did.
At this time, the position of the transistor is such that the distance D between the transistor end and the metal circuit end of the half line L drawn from the center of gravity of the transistor in an arbitrary direction is compared with the distance W from the center of gravity of the transistor to the end of the transistor. The largest half-line (that is, the half-line having the largest D / W, and if there are multiple D / W, select an arbitrary one) as the half-line L1, and the counterclockwise direction is 9
0 degree (half line L2), 180 degree (half line L1 '), 270
Draw a half line that forms an angle of degrees (half line L2 ') and
D (D1) and W (W1) above and D (D
1 ') and W (W1'), D1 = D1 ', W1 = W
Arrange so as to be 1 ', similarly D2 = D2', W2 = W
Arranged to be 2 '. Table 1 shows the results of measuring the thermal resistance of the prepared module.

[0029]

[Table 1]

As is clear from the results shown in Table 1, the power modules according to Examples 1 to 4 are excellent in heat dissipation and have high reliability. In addition, comparing Examples 1 and 2, it is clear that Example 2 has better heat dissipation.
Further, comparing Examples 3 and 4, Example 4 is superior in heat dissipation. On the other hand, the power modules using the circuit boards according to Comparative Examples 1 and 2 cannot obtain sufficient heat dissipation, and thus cannot cope with high integration and high output of semiconductors.

[0031]

EFFECTS OF THE INVENTION According to the present invention, it is not necessary to use a ceramic substrate having a particularly high thermal conductivity, and it has sufficient durability against damage caused by thermal shock such as heat shock or heat cycle and thermal history. Moreover, it is possible to easily provide a highly reliable power module which has excellent heat dissipation and is less likely to cause insulation failure such as insulation breakdown caused by damage to the ceramic substrate.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a power module of the present invention,
(A) is a plan view and (b) is a cross-sectional view taken along line AA ′ in (a).

[Explanation of symbols]

1: Semiconductor chip 2: Solder 3: Metal plate 4: Ceramic substrate 5: Heat sink 6: sealing resin L: An example of a half line passing through the center of gravity of the semiconductor chip D: Distance between end of semiconductor chip and end of metal circuit W: Distance from center of gravity of semiconductor chip to edge G: Center of gravity of semiconductor chip

Claims (4)

(57) [Claims] 1. A power module in which a metal circuit is provided on at least one main surface of a ceramics substrate, and a semiconductor chip is arranged on the metal circuit. The power module is viewed from a direction perpendicular to the substrate. , A half line is drawn in an arbitrary direction from the center of gravity of the semiconductor chip, the distance between the end of the semiconductor chip and the end of the metal circuit on the half line is D, and the distance from the center of gravity of the semiconductor chip to the end is W. When you do, D
A power module, wherein the semiconductor chips are arranged so that at least one half line satisfying ≧ W exists. 2. The power module according to claim 1, wherein the semiconductor chips are arranged so that two or more half lines satisfying D ≧ W are present. 3. The power module according to claim 1, wherein the semiconductor chip is arranged so that a half line satisfying D ≧ W exists in all directions. 4. The power module according to claim 1, wherein the ceramic substrate is made of an aluminum nitride sintered body or a silicon nitride sintered body.