JPH10223809A - Power module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability power module, which has a full durability to damage, which is generated by a thermal shock, such as a heat shock and a heat cycle, and a thermal hysteresis, and moreover, is superior in heat dissipation property and hardly generates an insulation failure. SOLUTION: This power module is one constituted into a structure, wherein a metallic circuit is provided on at least one major surface of a ceramic board 4 and a semiconductor chip 1 is disposed on said metallic circuit. The power module is seen from the direction vertical to the board 4, a half straight line L is drawn from the center of gravity of the chip 1 to an arbitrary direction and when the distance between the end part of the chip 7 and the end part of the metallic circuit is assumed D on the half straight line L and the distance between the center of gravity of the chip and the end part of the chip is assumed W, the above chip 1 is disposed in such a way that the half straight line, which is formed on the condition of D>=W exists at least one or more. Preferably, the board 4 is formed using a sintered body of an aluminium nitride film or a silicon nitride film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power module which requires high reliability and heat dissipation when mounting electronic components such as semiconductor chips having high heat generation.

[0002]

2. Description of the Related Art Conventionally, alumina (Al ₂ O ₃ ), aluminum nitride (Al
A circuit board is widely used in which a ceramic sintered body such as N) or beryllium oxide (BeO) is used as a substrate, and a circuit board made of copper (Cu) or the like is integrally joined as a conductive layer on the surface thereof.

In a circuit board using an alumina sintered body, a circuit board is formed of a metal such as Cu having excellent heat conductivity and electric conductivity, so that circuit operation delay is small and circuit wiring life is long. For a long time, it has good wettability to bonding materials such as solder and can bond a semiconductor chip (IC element) or an electrode plate to the surface of the ceramic sintered body with high bonding strength. As a result, heat generated from the semiconductor chip can be reduced. It is possible to maintain good radiation performance and semiconductor chip operation reliability.
Further, by joining a metal plate such as Cu to the back surface of the ceramic substrate, there is an advantage that the objects of stress relaxation and thermal deformation prevention of the ceramic substrate can also 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. If the thermal conductivity of the ceramic substrate is small, the heat dissipation becomes insufficient, resulting in a low thermal resistance. As a result, there is a problem that the semiconductor chip cannot cope with high output of the semiconductor chip.

For the above reasons, the use of a ceramic sintered body having a high thermal conductivity for the substrate has attracted attention, and the use of an aluminum nitride sintered body and the improvement of the thermal conductivity of a conventional ceramic sintered body such as alumina have been increasing. It is being planned. In the case of ceramic substrates such as aluminum nitride, in order to increase the thermal conductivity in order to obtain high heat dissipation, it is necessary to reduce impurities in the ceramic substrate, reduce crystal grain boundaries, and increase the size of crystal grains. However, when the crystal grain boundaries are reduced and the crystal grains are enlarged, there is a problem that the strength of the ceramic substrate is reduced.

In particular, an aluminum nitride circuit board using aluminum nitride as a ceramic substrate has sufficient durability against damage caused by heat shock and heat history such as heat shock and heat cycle.
There has been reported an example in which the thickness of a bonding layer interposed between a Cu circuit and an aluminum nitride substrate is increased to, for example, 20 μm or more (see JP-A-6-196828). However, when the thickness of the bonding layer is increased, there are problems that it becomes difficult to remove unnecessary brazing material in a subsequent process and that thermal resistance increases.

[0007]

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

That is, an 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 excellent heat dissipating property, and to prevent breakage of a 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]

SUMMARY OF THE INVENTION The present invention is a power module having a metal circuit provided on at least one main surface of a ceramic substrate, and a semiconductor chip disposed on the metal circuit. When viewed from a direction perpendicular to the semiconductor chip, a half line L 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 L is D, A power module characterized in that the semiconductor chips are arranged so that at least one half line satisfying D ≧ W exists when a distance from the center of gravity to the end is W.

[0010] Preferably, the power supply module is characterized in that the semiconductor chips are arranged so that two or more half-lines satisfying D ≧ W are present. A power module, wherein the semiconductor chips are arranged so that a half line satisfying ≧ W exists.

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

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. 1A and 1B are diagrams showing an example of a power module according to the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along a dotted line AA ′ in FIG. In the present invention,
Half line L drawn in any direction from the center of gravity G of the semiconductor chip
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 that the semiconductor chip is arranged on the metal circuit so that at least one or more half lines satisfying D ≧ W exist. According to the study by the present inventors, a power module that achieves the object of the present invention can be obtained only when the above condition is satisfied.

Although the reason for this is not clear, 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 radiation is reduced. Therefore, the greater the number of half-lines satisfying the above condition, the more the heat radiation effect is expected. However, according to the results of the studies by the inventors, the effect is remarkable with two or more lines, and D The heat radiation effect is most expected when the arrangement is such that a half line satisfying ≧ W is present, 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 200W.
It is particularly effective when the value exceeds.

For a power module having a plurality of semiconductor chips mounted thereon, the arrangement of the semiconductor chips exhibiting the largest amount of heat on the metal circuit may satisfy the above-described conditions. The arrangement may be such that it satisfies the above conditions, and it is of course better if the arrangement satisfies the above conditions for all the semiconductor chips. In particular, when two or more semiconductor chips having a heating value of more than 200 W are mounted, it is further desirable that any of the chips satisfies the above arrangement structure.

When a plurality of semiconductor chips are mounted on one metal circuit, the spacing between the semiconductor chips is, for example, two adjacent semiconductor chips in order to ensure sufficient heat dissipation of each semiconductor chip. Assuming that the distances from the center of gravity of each chip to the end of the semiconductor are Wa and Wb, respectively.
What is necessary is just to arrange so that it may become (Wa + Wb) or more. That is,
(Wa + Wb) may be replaced with the above D and arranged.

As the ceramic sintered body of the present invention, any material having electrical insulation and excellent 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 preferable in order to exhibit good heat dissipation, and a ceramic firing material having a bending strength of 350 MPa or more is required to secure strength after forming a circuit board. Consolidation is preferred.

Among these ceramics sintered bodies, aluminum nitride sintered bodies have high thermal conductivity and are therefore effective for use in high-output power modules, while silicon nitride sintered bodies have slightly lower thermal conductivity but higher bending strength. It is effective because it is large. In particular, a silicon nitride sintered body has a smaller coefficient of thermal expansion than a ceramic sintered body such as an aluminum nitride sintered body, so that the obtained power module has a higher resistance to thermal shock and is more excellent in reliability. It is.

The bonding layer of the present invention is generally formed using a brazing material paste. The brazing material paste is, for example, a material of a metal circuit board or a metal radiator plate is C
In the case of u, it is a brazing material containing Ag or Ag and Cu, preferably the above-mentioned brazing material containing an active metal such as Ti, Zr, and Hf.

As the material of the metal circuit board and the metal radiator formed on the ceramics substrate, metals such as copper, nickel, aluminum, molybdenum, and tungsten or alloys containing the above metals as main components can be used.

The manufacturing method of the power module according to the present invention will be described by way of an example. First, a brazing material paste containing Ag, Cu, and Ti as an active metal is applied to the entire surface of a ceramic substrate (a sintered body processed to have a maximum surface roughness of about 10 μm or less), and then has a sufficient width to cover the paste surface. Then, a solid metal plate (Cu) is placed in contact. The ceramic substrate on which the solid metal plate is arranged is heat-treated to produce a joined body of the two.

A circuit pattern is screen-printed on the metal plate of the joined body manufactured as described above using an etching resist to form a resist circuit pattern. The circuit pattern structure at this time conforms to claims 1 and / or 2.

Next, after an unnecessary metal or brazing material outside the pattern is removed by etching, 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 as necessary.

Next, cream solder is applied to a heat sink to which a solder resist has been attached, and the above-mentioned circuit board is placed and heated to be joined. Further, the semiconductor chip coated with the cream solder is placed at a predetermined position, and is subjected to heat treatment and joined, and then a lead wire is joined to the semiconductor chip. Cream solder is applied to the electrodes of the resin case in which the electrodes are embedded, covered with a heat sink, and heat-treated to be joined. Finally, resin sealing is performed to form a power module.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0025]

【Example】

[Examples 1 to 4, Comparative Examples 1 and 2] Thermal conductivity 130 W / m
K, an Ag-Cu-based brazing material paste containing active metal (Ti) is applied to both sides of a sintered aluminum nitride body having a thickness of 0.635 mm and a size of 50 x 60 mm by a screen printing method, dried, and then dried. A 3 mm metal circuit Cu plate and a 0.15 mm thick metal heat dissipation Cu plate are placed in contact with each other,
Heat treatment was performed at 830 ° C. for 30 minutes in a vacuum to obtain a joined body of the aluminum nitride substrate and the Cu plate.

An ultraviolet-curable etching resist was printed on a Cu plate of the joined body by a screen printing method and cured. The circuit pattern at this time is 24 ×
42 mm, 32 × 42 mm or 24 × 30 mm. After that, unnecessary ferrous chloride solution other than the pattern
u was removed. Next, the unnecessary brazing material between the Cu circuit patterns was removed with an aqueous solution containing ammonium hydrogen fluoride and hydrogen peroxide, and then the resist was removed. In addition, electroless N
A Ni protective film was selectively formed at a predetermined position of the Cu circuit by i-plating.

According to the above operation, the aluminum nitride circuit boards shown in Examples 1 and 2 and Comparative Example 1 in Table 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 power module is manufactured by mounting a transistor having a bottom area of 16 × 20 mm as a heat source on the center surface of the metal circuit of these circuit boards and soldering a 2.5 mm thick Cu plate as a heat sink on the back surface. did.
At this time, the position of the transistor is such that the distance D between the end of the transistor and the end of the metal circuit in the half-line L drawn in an arbitrary direction from the center of gravity of the transistor is smaller than the distance W from the center of gravity of the transistor to the end of the transistor. The largest half line (ie, the half line having the largest D / W, and if there is more than one, select any one line) is defined as the half line L1,
0 degree (half line L2), 180 degree (half line L1 '), 270
Draw a half line at the angle of degree (half line L2 ') and draw the half line L1
D (D1) and W (W1) above, and D (D
1 ′) and W (W1 ′), D1 = D1 ′, W1 = W
1 ′, and 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 evident from the results shown in Table 1, the power modules according to Examples 1 to 4 have excellent heat dissipation and high reliability. Further, when Examples 1 and 2 are compared, it is clear that Example 2 has better heat dissipation.
Further, when 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 do not provide sufficient heat dissipation, and thus cannot cope with high integration and high output of semiconductors.

[0031]

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 heat shock and heat history such as heat shock and heat cycle. In addition, it is possible to easily provide a highly reliable power module that has excellent heat dissipation and is unlikely to cause insulation failure such as insulation breakdown due to breakage of the ceramic substrate.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a power module according to the present invention;
(A) is a plan view, (b) is a cross-sectional view taken along 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 the end of the semiconductor chip and the end of the metal circuit W : Distance from the center of gravity of the semiconductor chip to the end G: Center of gravity of the semiconductor chip

Claims (4)

[Claims] 1. A power module having a metal circuit provided on at least one main surface of a ceramic substrate and a semiconductor chip disposed on the metal circuit, wherein the power module is viewed from a direction perpendicular to the substrate. Draw a half-line in an arbitrary direction from the center of gravity of the semiconductor chip, D represents the distance between the end of the semiconductor chip and the metal circuit end on the half-line, and W represents the distance from the center of gravity of the semiconductor chip to the end. When D
A power module, wherein the semiconductor chips are arranged so that at least one or more semi-straight lines satisfying ≧ W exist. 2. The power module according to claim 1, wherein the semiconductor chips are arranged so that two or more half-lines satisfying D ≧ W exist. 3. The power module according to claim 1, wherein the semiconductor chips are 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.