JP2541823B2 - Ceramic wiring board - Google Patents

Description

TECHNICAL FIELD The present invention relates to a ceramic wiring board, and more specifically,
The present invention relates to improvement of ceramic wiring boards used for high-density circuit boards, semiconductor packages, and the like.

[Prior art]

Conventionally, in forming a wiring pattern on a ceramic wiring board, a thick film method in which a conductor paste of a refractory metal is printed on the surface of a green sheet by a screen printing method and then baked is employed.

Further, in the case of attaching a metal fitting such as a lead pin or a heat sink to such a wiring board, a method of brazing to the wiring layer with a brazing material such as silver brazing is employed.

In recent years, a ceramic wiring board is required to have a high density wiring pattern like an integrated circuit such as an LSI. Therefore, a thin film method using an ion plating method, a sputtering method or the like is used instead of the thick film method. Proposed.

Specifically, this thin film method is applied to the surface of a ceramic substrate with T
An adhesive layer such as i, Cr and a thin film layer of a barrier layer such as Ag, Cu, Ni, Pd, etc. are provided by sputtering, etc., and a wiring pattern is formed on these layers by photolithography, and then an Au plating layer is used as a main conductor layer. Is applied to form a high-density wiring layer.

[Problems to be Solved by the Present Invention] However, when the lead pins, the heat sink, and the like are attached to the high-density wiring board made of a thin film by such a conventional technique, various problems occur. That is,
In the above thin-film conductor, under brazing conditions such as silver brazing, for example, in a reducing atmosphere, at 500 to 1000 ° C., distortion occurs due to the difference in coefficient of thermal expansion between layers of the wiring layer, and mutual thermal diffusion of metal atoms between the layers. As a result, the physical properties of each layer were changed, and defects such as discoloration, swelling, and peeling of the wiring layer occurred. Further, depending on the combination of the adhesive layer and the barrier layer of the wiring layer, the heat diffusion direction becomes unidirectional, and cavities (Kirkandall voids) are generated in either layer, which causes a problem such as a decrease in film strength.

Furthermore, when a lead pin or the like is brazed with silver and then a metal film such as Ni plating is further formed, there arises a problem that the strength is extremely lowered due to the film stress of the provided metal film.

[Object of the Invention]

Therefore, the main object of the present invention is to solve the above-mentioned problems. Specifically, a ceramic wiring substrate provided with a thin-film wiring layer to which lead pins, heat sinks, etc. can be attached and which has excellent film strength is provided. The present invention aims to provide a high density ceramic wiring board.

[Means for solving problems]

As a result of repeated studies on the above problems, the inventors of the present invention have found that a wiring board having a three-layer structure including an adhesive layer, a barrier layer, and a main conductor layer is used for a wiring board that requires mounting of metal fittings such as a lead pin and a heat sink. And the adhesive layer is Ti and the barrier layer is Ti and W
, And the main conductor layer mainly composed of Cu shows excellent heat resistance under the brazing heat treatment conditions, and the wiring layer itself can be silver brazed such as lead pins. It was found that a wiring layer having an excellent film strength with a small decrease in film strength is formed even when forming a metal film.

〔Example〕

FIG. 1 is a sectional view of a wiring layer of a ceramic wiring board according to the present invention. The wiring layer in the present invention basically has a three-layer structure. That is, the adhesive layer 2 and the barrier layer 3 are provided on the ceramic substrate 1 by a known vapor phase growth method such as an ion plating method and a sputtering method.
Further, the main conductor layer 4 is provided. The adhesive layer 2 is for improving the adhesiveness with the ceramic substrate 1, and the barrier layer 3 is provided for preventing mutual diffusion between the adhesive layer 2 and the main conductor layer 4.

According to the present invention, it is important to use Ti for the adhesive layer 2, an alloy of Ti and W for the barrier layer 3, and Cu for the main conductor layer 4.

That is, according to the above configuration, the adhesive layer 2 and the barrier layer 3 are similar in coefficient of thermal expansion and are unlikely to cause thermal diffusion, so that even under severe heat treatment conditions such as brazing during metal attachment. Thus, it is possible to obtain a wiring layer having excellent heat resistance, in which distortion between layers is prevented from occurring and mutual heat diffusion is prevented, and discoloration, swelling, peeling, and adhesion failure do not occur.

Moreover, since the barrier layer 3 is composed of Ti and W, the flexibility of the barrier layer itself is enhanced, and the internal stress of the surface film can be absorbed, so that the film strength is excellent even when the metal film is formed after the silver brazing. Is obtained.

The composition of the Ti-W alloy in the barrier layer is desired to have a Ti content of 0.2 to 30% by weight, particularly 3 to 18% by weight. When the Ti content is less than 0.2% by weight, the Ti layer as an adhesive layer is used. Adhesion strength with and decreases above 30% by weight, the hardness of the film increases, and the internal stress of the film formed thereon tends to be difficult to relax.

Further, the main conductor layer is mainly composed of Cu,
It is also possible to provide Au, Pt, Pd, and Ni on the Cu layer and use this as the main conductor layer.

The thickness of each layer of the wiring layer in the present invention should be formed to such an extent that each purpose can be sufficiently achieved. Specifically, the adhesive layer is 0.01 to 1.0 μm, particularly 0.03 to 0.5 μm, and the barrier layer is 0.1 to 5 μm, especially 0.5 to 2 μm, the main conductor layer is 0.1
˜10 μm, especially 0.5 to 5 μm is desirable, and the total thickness of the wiring layer is preferably 0.2 to 16 μm.

As a specific method for manufacturing a wiring board in the present invention, an adhesive layer made of Ti and having a predetermined thickness is provided on a cleaned ceramic substrate by a vacuum deposition method or a sputtering method.

Next, a layer made of an alloy of Ti and W is provided as a barrier layer by the same means. This alloy layer is formed, for example, with Ti and W.
Can be easily formed by sputtering using an alloy target prepared in a predetermined ratio. After forming the barrier layer, a Cu main conductor layer is subsequently provided by sputtering.

Then, a wiring pattern is formed by photolithography or the like, and the metal fitting is brazed with silver at 700 to 1050 ° C. in a reducing atmosphere such as wet hydrogen or humidified forming gas (H ₂ / N ₂ ).

After that, if desired, a noble metal layer such as Au, Pt, or Pd is provided for the purpose of preventing oxidation, improving solder wettability, and wire bonding property, thereby completing the process.

 The invention is illustrated by the following example.

Example-Preparation of sample An adhesive layer of Ti, a barrier layer of Ti-W alloy and a main conductor layer of Cu were formed on the surface of a substrate made of a cleaned Al ₂ O _{3 based} sintered material by sputtering. Set up according to. Then, 1 × 1 mm dot pattern processing was performed by photolithography.

The brazing strength and the film strength of the obtained sample were measured by the following methods.

(Brazing strength) Kovar metal fittings were brazed to the dots of the obtained sample using silver brazing (BAg-8 or Ag) at 850 to 1030 ° C for 10 minutes (wet arm gas atmosphere). Then, 1 μm of Ni and 2 μm Au were provided by plating. Next, the metal fitting was pulled in the vertical direction, and the tensile strength of the metal fitting to the wiring layer was measured.

(Film strength) Each of the obtained samples was subjected to a reducing atmosphere at 850 to 1030 ° C.
After 10 minutes of heat treatment, a 1 μm Ni layer and a 2 μm Au layer were sequentially formed on the dot portion. Then, a metal fitting for measurement was soldered to the dot portion, the metal fitting was pulled vertically, and the tensile strength was measured.

According to Table 1, Ti-Pd-Au system (No. 31) and Ti-Ni-Au system (No. 3) are examples of conventional wiring board configurations.
In 2), the film strength was 1 Kg / mm ² or less, whereas the sample of the present invention showed excellent strength. According to the sample of the present invention, it was confirmed that the strength varies depending on the Ti content in the barrier layer, and the Ti content of 0.2 to 30% by weight, particularly 3 to 18% by weight, shows excellent strength. I understand. There is not much difference in the thickness of each layer, but the adhesive layer is 0.01-1.0 μm,
When the barrier layer deviates from the range of 0.1 to 5 μm and the main conductor layer deviates from the range of 0.1 to 10 μm, the strength tends to decrease.

The wiring layer is Ti (0.05 μm) -Mo (1.5 μm) / Cu.
(0.5 μm) -Ni (0.5 μm) also shows excellent strength, and this system has a brazing strength (without plating after mounting metal fittings) of 5.26 Kg / mm ² , but like this example.
When Ni-Au plating was performed, the strength was remarkably decreased to 3.49 Kg / mm ² , whereas the samples of the present invention showed a small decrease.

〔The invention's effect〕

As described in detail above, in the ceramic wiring board of the present invention, by forming the wiring layer from the composite layer made of the above-mentioned specific metal, the wiring layer of the metal such as the lead pin and the heat sink of the ceramic semiconductor storage package can be formed. When applying to a wiring board that requires mounting, a harsh heat treatment process when brazing metal fittings, such as 50 in a reducing atmosphere
Strain generation between each layer of the wiring layer under the condition of 0 ~ 1030 ℃,
By suppressing the mutual heat diffusion, discoloration, swelling, peeling, etc. of the wiring layer can be prevented and the adhesion with the ceramic substrate can be improved. Also,
Even when a metal layer is formed on the surface of a lead pin or the like by plating or the like, it is possible to prevent the strength of the wiring layer from being lowered and maintain excellent strength. This enables brazing of metal fittings such as lead pins and the formation of a metal layer directly on the wiring layer, so that a high-density semiconductor package can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a sectional view of a wiring layer in a ceramic wiring board of the present invention. 1 ... Ceramic substrate 2 ... Adhesive layer 3 ... Barrier layer 4 ... Main conductor layer

Claims (1)

(57) [Claims] 1. An adhesive layer made of Ti on a ceramic substrate,
A ceramic wiring board having a wiring layer formed by sequentially providing a barrier layer made of an alloy of Ti and W and a main conductive layer mainly containing Cu.