JPH0227817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for bonding input/output electrical connection pins on a package substrate, and more specifically, for bonding connection pins of a multilayer ceramic substrate to the substrate. This relates to the joining means.

(Prior Art) With the recent miniaturization, high-density, and high-speed performance of computer systems, the requirements for package boards at the mounting level are becoming increasingly strict. Specifically, there are demands for increasing wiring density and miniaturizing signal line widths on package boards, lowering the resistance value of signal line conductors, and lowering the dielectric constant of insulating materials. Package board technology has been developed. For example, multilayer ceramic substrates using alumina green sheets, low-temperature sintered multilayer ceramic substrates that can be sintered at around 900℃ using glass ceramic green sheets, and gold and silver-palladium conductors can be used, and thin films such as spatter deposition on ceramic substrates. Package board using technology,
Furthermore, there are package substrates made of organic insulating materials (polyimide, etc.) in combination with thin film conductors. Many VLSI chips will be mounted on such high-density, miniaturized mounting boards.
Therefore, the number of input/output terminals for electrical connection to the outside of the board becomes extremely large. Therefore, a technology has been developed in which input/output terminals are formed using pins on the back surface of a multilayer board.

As a conventional technique for attaching connection pins to this multilayer ceramic substrate, for example, connection pins made of a material such as Kovar 4.2 alloy were attached to an alumina multilayer substrate using silver solder. Figure 1 shows
This is a diagram for explaining a conventional method, and shows a ceramic substrate 1 and a ceramic substrate after conductor pads made of molybdenum or tungsten formed on an alumina green sheet and conductors in through holes are sintered in a reducing atmosphere at a temperature of 1500°C or higher. A conductor 2, such as molybdenum or tungsten, is shown. A nickel layer 3 is formed on this conductor pad part by plating,
Next, connecting pins 5 made of Kovar or 4.2 alloy are attached using silver solder 4. The composition of silver solder is generally a eutectic alloy of 60 mol% Ag - 40 mol% Cu, with a melting point of 779°C and a brazing temperature of about 810°C. It is carried out in a reducing atmosphere. The connection pins and conductors attached to the board are then gold-plated to prevent deterioration. FIG. 2 shows a substrate with connection pins on which a gold layer 6 is formed. This method requires a high brazing temperature, and it is difficult to heat fine thin film patterns formed on the substrate to this temperature.On the other hand, pins are attached to the substrate in advance and then fine thin film patterns such as signal lines are formed. Even in this case, the accuracy when forming various patterns on the pin-equipped substrate deteriorates, and the workability also deteriorates. The same applies to packaging technology in which a pattern is formed on a multilayer ceramic substrate using an organic insulating film (polyimide or the like). Furthermore, it involves a step of gold plating the connection pins and conductor pads after brazing, resulting in poor workability.

Next, in order to lower the processing temperature, Au was used as a brazing material.
−Sn or Au−Si, Au−Sn−Pd, Au−Sn−Ag
etc. were considered. A specific example is shown in FIGS. 3 and 4. In Fig. 3, the ceramic substrate 1
A molybdenum layer 12 is attached to the surface of the substrate 1, and a nickel coating 13 is formed on the molybdenum layer by a plating method or the like. Next, a gold coating 14 is formed on the nickel coating using gold paste, and a gold/nickel solid solution is formed by heat treatment. Subsequently, connection pins 16 coated with gold plating 17 are connected using Au--Sn brazing material 15. In this method, the gold-nickel solid solution is formed at a temperature of about 700°C under hydrogen reduction. Further, in FIG. 4, a molybdenum layer 22 is attached to the surface of a ceramic substrate 21, a nickel film 23 is formed on the molybdenum layer, and a gold film 24 for a barrier is formed on the nickel film. On the gold coating, Sn
After being coated with a group metal layer 25 serving as a source of gettering metal, a connecting pin 27 plated with gold 28 is bonded by an Au--Sn brazing material 26. In all of these methods, metal must be formed as an intermediate layer, which is disadvantageous in terms of cost. In addition, a molybdenum pad must be formed in advance on the pad where the connecting pin is attached, which is disadvantageous in terms of process and cost.Furthermore, during heat treatment such as brazing, hydrogen is used to prevent molybdenum from oxidizing. It had to be done in a reducing atmosphere. Furthermore, in order to provide good adhesion between the molybdenum pad and the ceramic substrate, additives such as glass frit must be included in the molybdenum paste, resulting in the problem of increased conductor resistance.

(Objective of the Invention) The object of the present invention is to eliminate such conventional drawbacks, to enable heat treatment at a lower temperature (400°C or less) and in a neutral atmosphere than the conventional method using silver brazing material, and to It has a very simple structure that does not require gold coating for barriers as shown in the conventional method of An object of the present invention is to provide a brazing method having adhesive strength.

(Structure of the Invention) That is, a step of forming a titanium film on the part to be brazed on the ceramic substrate of the present invention, a step of forming a palladium metal layer on the titanium film, and a step of forming a palladium metal layer on the input/output electrical connection pin using a brazing material. This is a brazing method characterized by comprising a step of brazing on the layer.

(Examples) The present invention will be described in detail below based on Examples.

5 to 8 are diagrams showing the brazing method of the present invention, and FIG. 9 is a schematic diagram of a ceramic substrate with pins produced in an example. As shown in FIG. 5, a mask 32 with a blank area for brazing, which is formed by etching a thin metal plate, is placed on the ceramic surface of a multilayer ceramic substrate 31. The multilayer ceramic substrate 31 may be made of an alumina green sheet printed with molybdenum or tungsten as a conductor, laminated and pressed, and then sintered in a hydrogen reducing atmosphere at 1500°C or higher, or made of lead borosilicate crystallized glass and alumina. Gold, silver, silver-palladium, gold-platinum, silver-platinum, etc. are printed as conductors using glass-ceramic green sheets.
A so-called low-temperature sintered multilayer ceramic substrate sintered in an oxidizing atmosphere at temperatures below 0.degree. C. may also be used. Here, the latter substrate using silver-palladium was used. Next, a titanium film was formed. As shown in FIG. 6, a titanium film 33 having a thickness of 300 Å to 1000 Å is formed by sputtering on the mask superimposed on the ceramic substrate. Continuing on from the titanium film formed in FIG. 6, a palladium layer 34 is formed from among the metals of the group of the periodic table, as shown in FIG. The palladium layer was formed to a thickness of 1000 Å to 3000 Å by sputtering similar to that used for forming the titanium thin film. After reducing the sputtering temperature to below 10 ^-5 torr, Ar gas was introduced to about 10 ^-2 torr.
FIG. 8 shows a cross-sectional view when the mask is removed after forming a titanium thin film and a palladium metal film. As can be seen from FIG. 8, in this method, a titanium film is formed directly on the surface of the ceramic substrate, and this is one of the features that is significantly different from other methods. The ceramic substrate having the metal pad portion obtained in this way is then coated with a plurality of materials such as Kovar or 4.2 alloy, each having about 1 to 3 mg of alloy brazing filler metal 35 with a weight ratio of 80% gold and 20% tin. It is placed on pins 36 for input/output electrical connections and bonded onto a layer of palladium, which is a group metal. FIG. 9 shows a schematic diagram of a multilayer ceramic substrate with connecting pins attached by the above method, and the surface of the metal pin 36 is coated with a gold film layer 37 formed by plating or the like. . The processing temperature for brazing is 300°C to 300°C, since the melting point of an alloy brazing filler metal with a weight ratio of 80% gold and 20% tin is 280°C.
It was carried out for 10-30 minutes at a temperature range of 450°C. The palladium layer causes gettering of the tin in the gold-tin brazing material, increasing the apparent ratio of gold to tin and thus increasing the melting point of the brazed joint after cooling or condensation of the brazing material. effective. This is effective in cases where there is a step of applying a thermal cycle after attaching the pin. In addition, the gold coating layer applied to the connection pins also
During the brazing process, the gold coating layer partially melts together with the gold-tin brazing material, increasing the proportion of gold-tin in the brazing material and raising the melting point of the bonded portion, producing the same effect. The adhesive strength between the input/output electrical connection pins brazed using this method and the multilayer ceramic substrate is 4.0.
Kg/mm ² or more, indicating sufficient strength as input/output pins for mounting boards.

(Effects of the Invention) As described above, by adopting the brazing method of the present invention, the brazing process can be performed at an extremely low temperature of 400°C or less and in a neutral atmosphere, and pin pads can be formed on the surface of the ceramic substrate. thick film metals (molybdenum, tungsten, gold, silver, silver)
It has now become possible to obtain a pinned substrate with sufficient adhesive strength that has a simple structure that does not require the prior formation of a layer (such as palladium) and does not require a gold coating for a barrier. Furthermore, since the method of the present invention does not involve wet processes such as etching when forming the metal layer of the pin pad, it does not have any adverse effects on the ceramic and can provide a highly reliable substrate with pins. It has become advantageous in terms of cost, and it has become possible to obtain a pinned board that is sufficiently strong against thermal cycles after pinning.

Furthermore, instead of sputtering, film forming means such as timed vapor deposition, plating, and screen printing can be used.

[Brief explanation of drawings]

1 to 4 are diagrams showing conventional pinned ceramic substrates, FIGS. 5 to 8 are diagrams showing the method of the present invention, and FIG. 9 is a diagram showing the method of the present invention. FIG. 2 is a schematic diagram of a pin-equipped board. In the figure, 1, 11, 21, 31... Ceramic substrate, 2, 12, 22... Thick film conductor pad layer, 3, 13, 23... Nickel layer, 4... Silver solder, 5, 16, 27, 36...Metal pin, 6,1
7, 28, 37... Gold coating layer, 14... Gold coating,
15, 26, 35... Gold-tin wax, 24... Gold coating, 25... Group metal layer, 32... Mask, 3
3...Titanium film, 34...Palladium metal film.

Claims (1)

[Scope of Claims] 1. A method of brazing metal connection pins to a ceramic substrate using a brazing material, which includes the steps of forming a titanium film on the part to be brazed on the ceramic substrate, and depositing palladium metal on the titanium film. A brazing method comprising the steps of forming a film and brazing a connecting pin onto the palladium metal layer using a brazing material. 2. The brazing method according to claim 1, wherein the brazing material is a gold-tin brazing material.