JP3260224B2 - Circuit board manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a circuit board in which a metal circuit and a metal radiator plate are formed on a ceramic substrate.
It relates to the law.

[0002] In recent years, with the advancement of the performance of industrial equipment such as robots and motors, the transition of high-power modules such as high-power and high-efficiency inverters has been progressing, and the heat generated from semiconductor elements has been increasing steadily. . In order to efficiently dissipate this heat, various methods have conventionally been used for large power module substrates. In particular, since ceramic substrates having good thermal conductivity have become available recently, a metal plate such as a copper plate is bonded on the ceramic substrate, and after forming a metal circuit, the semiconductor substrate is subjected to a treatment such as plating or plating. A structure in which an element is mounted and a metal heat radiating plate for attaching a heat radiating fin to the opposite side of the circuit is being adopted.

[0003] There are various joining methods of metal and ceramics, but from the viewpoint of manufacturing circuit boards, Mo-Mn method, active metal brazing method, copper sulfide method, DBC method, copper metallizing method and the like can be mentioned. it can. In particular, in order to join a high thermal conductive aluminum nitride substrate and a copper plate, which are attracting attention in high power module substrates, a brazing material containing an active metal (hereinafter simply referred to as a “brazing material”) is interposed between the two. An active metal brazing method for forming a joined body by heat treatment (for example,
No. 177634), and a DBC method in which an aluminum nitride substrate and a copper plate whose surfaces are oxidized are heated and joined at a temperature lower than the melting point of copper and higher than the eutectic temperature of Cu-O (for example, JP-A-56-163093).
Publication No.) is adopted.

The active metal brazing method has the following advantages over the DBC method. (1) Since the processing temperature for obtaining the above joined body is low, the residual thermal stress caused by the difference in thermal expansion between the aluminum nitride substrate and the copper plate is small. (2) Since the brazing material is a ductile metal, it has high durability against heat shock and heat cycles.

[0005]

However, even if the active metal brazing method is used, it does not have sufficient durability against damage caused by heat shock and heat history such as heat shock and heat cycle. Nevertheless, a proposal for a new technology was awaited. Therefore, the volume of the metal circuit (usually provided on the upper surface of the ceramic substrate) is adjusted to 50 to 90% of the volume of the metal radiator plate formed on the opposite surface (JP-A-63-24815). The improvement was made to some extent by reducing the thickness of the plate to 50% or less of that of the metal circuit (Japanese Patent Application Laid-Open No. H5-170564).

However, in these techniques,
Since the material of the metal circuit and the metal radiator plate are both copper, changing the volume of both is equivalent to making the balance of stress due to thermal expansion different, so the thermal shock resistance of the circuit board itself is reduced. Although the metal circuit or the metal radiator plate is less likely to peel off due to the improvement, the warpage of the circuit board becomes remarkable due to the rapid temperature rise when soldering the semiconductor element to the metal circuit and the base copper plate to the metal radiator plate. , Thereby creating a gap between the metal heat sink and the base copper plate,
There was a risk that the part would become a void after soldering.

As a result of various studies to solve the above problems, the present inventors have focused on a bonding layer between a metal plate and a ceramic substrate which form a metal circuit and a metal radiator plate. It has been found that the thermal stress caused by the difference in the thermal expansion coefficient between the two can be absorbed by providing a specific gap therein . Therefore, further study
However, to provide a specific amount of voids in the bonding layer,
Organic bonding in brazing material paste used in metal brazing
The amount of the mixture is, for example, 3 to 5 times larger than the usual amount, or
Print brazing material paste in stripes or grids of fixed size
Or preferably both, so that
The above-mentioned gap can be easily formed, and surprisingly
Shows that the amount of warpage of the manufactured circuit board is also reduced.
The present invention has been completed.

[0008]

That is, according to the present invention, a metal circuit is joined to one side of a ceramic substrate, and a metal heat sink is joined to the other side by an active metal brazing method.
In the circuit board, the occupancy of diameter 1mm or more voids present in the junction layer is the volume of the entire bonding layer 0.3-3
% , The amount of warpage is -70 μm or less (however, how to warp the circuit board)
In the direction, the direction that is concave with respect to the metal circuit surface is expressed as “+”.
Shown. ), The following (a) and / or (b) hands
A method of manufacturing a circuit board , comprising providing a step . (A) Brazing material paste used in active metal brazing
Contains a metal component, an organic solvent and an organic binder,
The ratio of the mixture is 120 parts by weight in total of the metal component and the organic solvent.
4.7 to 7.3 parts by weight. (B) Brazing material paste used in active metal brazing
Is applied in the form of stripes or grids.
When the width (b) of the groove without the brazing material paste is
30 to 100 μm, and the interval (a) between the grooves is 3 to 5 mm
And

Hereinafter, the present invention will be described in more detail. As the ceramic substrate used in the present invention,
Examples thereof include an aluminum nitride substrate, a beryllia substrate, and an alumina substrate. Among them, an aluminum nitride substrate is preferable, and its density is desirably 95% or more in terms of mechanical strength and electrical characteristics. A suitable thickness of the ceramic substrate is about 0.4 to 0.7 mm.

On the other hand, the material of the metal circuit and / or metal radiator plate is copper, aluminum, tungsten, molybdenum or the like, but copper is generally used. As the thickness of the metal circuit, the current density has been increasing in recent years,
Thickness is more preferable, and the thickness of the metal radiating plate is 0.1 mm.
It is desirably 2 mm or less.

As a method of forming a metal circuit on one surface of the ceramic substrate and a metal heat radiating plate on the other surface, a method of etching a joined body of the ceramic substrate and the metal plate, a method of punching from the metal plate. After joining the pattern of the metal circuit and / or the metal radiating plate to the ceramic substrate, it can be performed by a method of peeling off an unnecessary metal portion. In these cases, the joining of the metal plate or the pattern and the ceramic substrate is performed using an active metal. A brazing method is employed .

The metal component of the brazing material in the active metal brazing method contains silver and copper as main components, and uses the active metal as a sub-component in order to ensure wettability with the ceramic substrate during melting. The active metal component reacts with the ceramic substrate to generate oxides and nitrides, and these products strengthen the bond between the brazing material and the ceramic substrate. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium, and compounds thereof. These ratios are 3 to 35 parts by weight of the active metal per 100 parts by weight of the total of 69 to 75 parts by weight of silver and 25 to 31 parts by weight of copper.

[0013] brazing material paste used in the active metal brazing method, the organic solvent agent and an organic binder in addition to the metal component of the brazing material, a roll, kneader, Banbury mixer, universal mixer, a stone mill, etc. Can be prepared by mixing. Examples of the organic solvent include methylcellosolve, terpineol, isophorone, and toluene, and examples of the organic binder include ethylcellulose, methylcellulose, and polymethacrylate.

In the present invention, means for forming voids having a diameter of 1 mm or more in the bonding layer include the following: (a) The amount of the organic binder in the brazing material paste used in the active metal brazing method is, for example, three times less than the usual amount. A method in which a fine solid of the organic binder is left by adding about 5 times larger amount to burn out the organic binder at the time of heat treatment for brazing; (b) when applying the brazing material paste on the ceramic substrate, Dozens of μm in advance
Write applied so that the grooves occurs in a striped or lattice pattern spacing
Law, or both (a) and (b). Striped or latticed
As shown in FIGS. 1 and 2, the coating pattern of
The interval (a) between grooves without material paste is 3 to 5 mm,
The width (b) of the groove without the brazing material paste is 30 to 100 μm.
And As a result, the gap of 1 mm or more in diameter is easily formed.
A specific amount can be formed, and the circuit board
The amount of warping is -70 μm or less (however, the warping direction of the circuit board is gold
The direction that is concave with respect to the generic circuit surface is displayed as “+”. )When
Become smaller. When the amount of warpage of the circuit board decreases,
The occurrence of voids after padding is drastically reduced.

In the present invention, the occupation ratio of the void having a diameter of 1 mm or more in the bonding layer between the ceramic substrate and the metal circuit and the bonding layer between the ceramic substrate and the metal radiating plate is 0.3 to the total volume of the bonding layer. It needs to be 必要 3%. If the occupation ratio of the voids exceeds 3%, the bonding strength between the ceramic substrate and the metal circuit or metal radiator plate will be weakened, and if it is less than 0.3%, the effect of absorbing the thermal stress will not be sufficiently exhibited.

In the present invention, the gap having a diameter of 1 mm or more can be measured by a soft X-ray, and the volume of the entire bonding layer can be obtained from SEM observation of a cross section of the circuit board.

[0017]

The present invention will be specifically described below with reference to examples and comparative examples. Examples 1-5 Comparative Examples 1-6 Each metal powder of silver, copper and zirconium, 75 parts by weight of silver powder, 25 parts by weight of copper powder, 5 parts by weight of zirconium powder,
15 parts by weight of terpineol (the total of these is 120
Parts. ) And a toluene solution of polyisobutyl methacrylate as an organic binder were added in solid content at the ratio shown in Table 1 and kneaded well to prepare a brazing material paste.
This brazing material paste is applied to an aluminum nitride substrate (51 × 3
Whether the entire surface is printed by screen printing on the circuit surface side (front surface) of 6 × 0.65 mm) (Examples 1 and 2, Comparative Example 1
2) or a grid-like pattern shown in Table 1 and FIG. 1 (Examples 3 to 5 and Comparative Examples 3 to 6), and the entire surface was applied to the heat radiation surface side (back surface). The coating amount (after drying) at that time is 6
８8 mg / cm ² .

Next, a copper plate (51 ×) for forming a metal circuit is formed on the surface of the aluminum nitride substrate on which the brazing material paste is applied.
36 × 0.5 mm) and a copper plate (51 × 36 × 0.2 mm) for a metal radiator on the back side, and then at a temperature of 900 ° C. under a vacuum of 1 × 10 ⁻⁵ Torr or less. 3
After heating for 0 minutes, the assembly was cooled at a temperature lowering rate of 2 ° C./min to produce a joined body.

Next, a UV-curable etching resist is applied on the copper plate of the joined body by screen printing.
Unnecessary portions of the copper plate are dissolved and removed by performing an etching process using a cupric chloride solution, and the etching resist is further reduced by 5%.
Peeled off with caustic soda solution. In the joined body after this etching process, there is a residual unnecessary brazing material or a reaction product between the active metal component and the aluminum nitride substrate between the copper circuit patterns.
To remove it, it was immersed in a 10% ammonium fluoride solution at a temperature of 60 ° C. for 10 minutes.

A circuit board manufactured through these series of processes is provided with a soft X-ray (“SV-X” manufactured by Softex Corporation).
100AW "Measurement conditions: voltage 30kV, current 3mA)
A gap having a diameter of 1 mm or more existing in the entire bonding layer was measured, and the resulting space was divided by the volume of the entire bonding layer obtained by observing the cross section of the circuit board by SEM to calculate the occupancy.
The peel strength was measured using a push-pull gauge.

Further, a heat cycle (thermal shock) test of the circuit board was performed. The heat cycle test was aerial, -4
After holding at 0 ° C. × 30 minutes, leave at 25 ° C. × 10 minutes, and further 12
After holding at 5 ° C. for 30 minutes, leaving as one cycle at 25 ° C. for 10 minutes, the number of heat cycles at which the copper plate started peeling was measured. Further, the amount of warpage of the circuit board when heated to 250 ° C. was measured by a non-contact laser displacement meter. Furthermore, the rate of void formation when a circuit board is soldered to a base copper plate having a thickness of 4 mm with no load in a reflow furnace at 250 ° C. [(void area) / (circuit board area) × 100]
The ultrasonic probe (“AT-7000” manufactured by Hitachi, Ltd.)
Was measured. Table 1 shows the results.

[0022]

[Table 1]

[0023]

According to the circuit board of the present invention, the rate of void generation when soldering the circuit board to the base copper plate can be remarkably reduced, the peel strength is large, and the thermal shock such as heat shock and heat cycle, heat shock, etc. The durability against the history is also sufficiently high.

[Brief description of the drawings]

FIG. 1 is a plan view showing a pattern of a brazing material paste applied on a ceramic substrate.

FIG. 2 is an enlarged view of FIG. 1;

[Explanation of symbols]

 Reference Signs List 1 Ceramic substrate 2 Line indicating groove without brazing material paste a Interval between grooves without brazing material paste b Width of groove without brazing material paste

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Kageyama 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture Inside the Omuta Plant of Electrochemical Industry Co., Ltd. (72) Inventor Katsunori Terano 1 Shinkaicho, Omuta-shi, Fukuoka Prefecture Electrochemical Industry Omuta Plant Examiner Shigeki Hayashi (56) References JP-A-59-126739 (JP, A) JP-A-2-140870 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05K 1 / 02 H05K 3/38

Claims (1)

(57) [Claims] A ceramic circuit is provided with a metal circuit on one side and a metal radiator on the other side by an active metal brazing method.
In the circuit board formed by bonding I, from 0.3 to 3% occupancy of diameter 1mm or more voids present in the junction layer is the volume of the entire bonding layer, warpage -70μm less (however
The direction of warping of the circuit board is concave with respect to the metal circuit surface.
The direction is displayed as "+". ), The following (a) and
And / or (b) means for applying a circuit board.
Manufacturing method. (A) Brazing material paste used in active metal brazing
Contains a metal component, an organic solvent and an organic binder,
The ratio of the mixture is 120 parts by weight in total of the metal component and the organic solvent.
4.7 to 7.3 parts by weight. (B) Brazing material paste used in active metal brazing
Is applied in the form of stripes or grids.
When the width (b) of the groove without the brazing material paste is
30 to 100 μm, and the interval (a) between the grooves is 3 to 5 mm
And