JPS594876B2 - Thick film circuit board and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thick film circuit board with excellent solder resistance and a method for manufacturing the same.

0 Thick-film circuit boards mainly consist of circuits made of gold paste and insulating paste, but gold paste has poor solder resistance, so its adhesion to the board tends to deteriorate, causing a loss in the reliability of semiconductor products. There were problems such as.

Therefore, it is conceivable to form a film of a substance with a lower diffusion coefficient for solder than the gold paste by vapor deposition, plating, etc. on the gold paste, but in that case, for example, on a thick gold film, the thick film is porous. Therefore, since a low-diffusion material is coated on top of this by vapor deposition or sputtering, the
Although there are some differences in degree, lattice defects are still formed due to the formation of a porous film and non-uniform cooling rate. However, since solder quickly diffuses along such holes and lattice defects, in vapor-deposited or sputtered films formed on thick gold films, solder, particularly Sn/Pb solder, is Difficult to achieve sufficient diffusion prevention effect. On the other hand, since the thick film is porous, electroplating on a thick insulator film may cause a short circuit with the lower electrode or the plating solution may remain in the pores, resulting in poor product reliability. There is zero risk of damage to the product, which is not desirable. Therefore, in a thick film circuit board where the gold paste layer and the insulating paste layer are exposed on the surface, forming only a coating by plating or a coating by vapor deposition or sputtering in order to improve solder resistance is in accordance with the above explanation in i5. As is clear from this, it was not desirable.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a thick film circuit board that has long-term reliability with respect to solder, and a method for manufacturing the same. That is, the present invention is a thick film circuit board comprising a gold paste layer and an insulating paste layer, and a plating layer of a metal whose diffusion coefficient is smaller than that of gold for solder on the exposed gold paste layer. A thick film circuit characterized in that the insulating paste layer is coated with a vapor-deposited film or a sputtered film of a metal whose coefficient of diffusion of the solder is larger than the coefficient of diffusion into the solder. The substrate and its manufacturing method include vapor deposition of a metal that has a lower diffusion coefficient than gold for solder, or a metal that diffuses faster than the solder into the solder, onto the circuit board. Alternatively, a metal with a diffusion coefficient smaller than that of gold for solder is selectively plated only on the gold paste that is not covered with an insulator by sputtering, and then the plated part and a predetermined area on the insulator are plated. The present invention provides a method for producing a thick film circuit board, characterized in that the vapor deposited film or the sputtered film is removed by selective etching in a portion other than a portion where a circuit pattern is to be formed. The present invention will be explained below based on an illustrated embodiment. FIG. 1 shows a thick-film circuit board that has not been subjected to solder-resistant treatment.A gold paste layer 2 and an insulator are placed on a semiconductor device substrate 1 so as to partially overlap the gold paste layer 2. A paste layer 3 is applied in each case. First, on the gold paste layer 2 and the insulating paste layer 3, a metal having a smaller diffusion coefficient than gold for the solder or a metal with which the solder diffuses at a higher rate than the rate at which the solder diffuses into the solder, for example, , a vapor deposited film or a sputtered film 4 having a thickness of 1 to 8 μm, for example, made of Ni, Cu, etc.
to be coated. In this case, in order to improve the adhesive strength, the vapor-deposited film or sputtered film 4 may be formed using a metal that is easily oxidized and has a strong bonding force with oxygen, such as Cr, Ti, Ni, etc., if necessary. The bonding layer 5 may be formed on the gold paste layer 2 and the insulating paste layer 3 by means such as vapor deposition or sputtering (see FIG. 2). Next, the photoresist layer 6 is patterned so that only the portions of the gold paste layer 2 not covered by the insulating paste layer 3 are opened (see FIG. 3).

Next, a plating layer 7 made of a metal having a diffusion coefficient smaller than that of gold for solder, such as Cu or Ni, and having a thickness of 5 to 15 μm, for example, is formed in the opening of the photoresist layer 6, and then the photoresist layer 6 is removed. (See Figure 4).
Next, an etching resist film 8 is formed by exposure and development only on the predetermined circuit pattern formation portions on the plating layer 7 and the insulating paste layer 3 (see FIG. 5), and the other portions are deposited or sputtered. 4 and the adhesive layer 5 are selectively etched away, and then the resist film 8 is removed (sixth
(see figure). As a result, the thick film circuit board has an insulating paste layer 3
The part of the gold paste layer 2 exposed from the solder is completely covered with a metal whose diffusion coefficient is smaller than that of gold for the solder.Moreover, due to the leveling effect of the plating layer 7 of this type of metal, the porosity of the gold paste layer 2 is lost. Further, since a product with few lattice defects can be obtained, solder diffusion can be significantly prevented, and the solder resistance is improved.

On the other hand, since the metal pattern formed on the insulator 3, consisting of a single vapor-deposited or sputtered film 4, is not exposed to the plating solution during the plating process, no plating solution remains and the metal below the insulator paste layer 3 is not exposed to the plating solution. There is no risk of poor insulation between the paste layer 2 and the paste layer 2. Note that since the vapor-deposited or sputtered film 4 is a porous film, it diffuses into the solder more quickly than the plating layer 7.

However, as a material for the vapor-deposited or sputtered film 4, Cu
, Ni, when Cu or Ni is used as a solder, for example, Sn
, Pb, In, etc., the diffusion coefficient of Sn, Pb, etc.
, In and other alloys are smaller than the diffusion coefficient of Cu and Nl, so the so-called Kirkendall board does not occur on the bonding surface of the insulating paste layer, and therefore the adhesion with the substrate will not be lost. . Since the thick film circuit board according to the present invention has good solder resistance as described above, it has long-term reliability.

[Brief explanation of drawings]

1 to 6 are sectional views of essential parts of a thick film circuit board showing the method of manufacturing a thick film circuit board according to the present invention in order of steps. In the figure, 1...substrate, 2...gold paste layer, 3...insulator paste layer, 4...
Vapor deposition or sputtering single layer, 5... Adhesive layer, 6
. . . Photoresist layer, 7 . . . Plating layer, 8 . . . Etching resist film.

Claims (1)

[Claims] 1. In a thick film circuit board in which a gold paste layer and an insulating paste layer are exposed on the surface, a plating layer of a metal having a diffusion coefficient smaller than that of gold for solder is provided on the exposed gold paste layer. A thick film circuit characterized in that a vapor deposited film or a sputtered film of a metal whose coefficient of diffusion of the solder is larger than the coefficient of diffusion into the solder is formed on the exposed insulating paste layer. substrate. 2. On a thick film circuit board with a gold paste layer and an insulating paste layer exposed on the surface, use a metal with a lower diffusion coefficient than gold for solder, or a metal whose diffusion coefficient is lower than the rate at which the solder diffuses into the solder. A larger metal is coated by vapor deposition or sputtering, and then the exposed gold paste layer is plated with a metal whose diffusion coefficient is smaller than that of gold for solder, and then this plated part and the insulating paste layer are soldered. A method for manufacturing a thick film circuit board, characterized in that the vapor deposited or sputtered coating is removed by etching except for the portion where the coating is applied. 3. The circuit board according to claim 2, wherein the step of forming a film by vapor deposition or sputtering is performed after forming an easily oxidizable metal film having a strong bonding force with oxygen on the circuit board in advance. Manufacturing method.