JPH057198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal screen used for printing a conductor pattern on a green sheet or the like of a hybrid module substrate.

[Background of the invention]

FIG. 6 is a manufacturing process diagram of a hybrid module substrate. As shown in this figure, first a green sheet is created (process), holes such as through holes are made in the green sheet (process), the through holes are filled with conductive paste (process), and then the screen is Print a conductor pattern using a printing method (process). A plurality of green sheets that have gone through these steps are stacked and pressed (step), cut into external shapes (step), and sintered (step). Note that the description of the subsequent steps will be omitted.

Now, the printing screen used for printing in the wiring printing process is described in the book "Basic Printing Technology" (Takahiro Tsunoda et al., published April 12, 1978).
As described in pp. 83-88, a screen (mesh) woven from silk, nylon, or polyester fibers, or stainless steel wire is stretched over a frame, a photosensitive emulsion is applied to the screen, a photomask is baked, and developed. It has been known.

Conventionally, a printing screen used for a substrate for a hybrid module has a stainless steel mesh 1 and a photosensitive emulsion 2, as shown in FIG.
Generally, it is coated with and patterned. However, it has become difficult for such printing screens to cope with the miniaturization of wiring patterns and the high precision of pattern shape and position in recent high-density hybrid module substrates.

Therefore, recently, a metal screen has been adopted in which a patterned metal mask 3 made of nickel or the like is attached to a stainless steel mesh 1 as shown in FIG. 8. In this metal screen, the printed thickness of the conductor pattern mainly depends on the thickness of the metal mask 3. The relationship between the metal mask thickness and printing thickness is illustrated in FIG. From this graph, 20μm
It can be seen that a metal mask thickness of 30 μm is required to obtain a print of .

Other factors that affect printing thickness include the characteristics of the conductive paste (viscosity, fluidity), squeegee shape,
There are squeegee pressure, squeegee hardness, gap between the metal mask and green sheet, etc., but the metal mask thickness has the strongest influence.

Now, in order to satisfy conditions such as the electrical resistance of the conductor pattern and the metallization strength after sintering, a printing thickness of about 20 μm is required, and the metal mask thickness of the metal screen is also 30 μm or more. When the metal mask becomes so thick, the printed conductor pattern tends to bleed when continuously printed, and this limits the number of times that continuous printing can be performed.

FIG. 10 is a graph showing the relationship between such metal mask thickness and the number of times that continuous printing can be performed. From this graph, metal mask thickness is 30μm, printing thickness is 20μm.
In this case, it is possible to print only twice in succession, which shows that the printing efficiency is very poor.

Here, the cause of the bleeding of the printed conductor pattern will be explained with reference to FIG. 11. Figure A is a cross-sectional view showing the metal screen set on the green sheet 4, and Figure B is a cross-sectional view showing the metal screen coated with the conductive paste 5. Figure C is a sectional view showing a state in which the conductive paste 5 is pushed out toward the green sheet 4 side and printed while moving the squeegee 6 in the direction of the arrow X. As the metal mask 3 becomes thicker, the metal mask 3 and the stainless steel mesh 1 become less compatible. Therefore, as shown in FIG. As a result of the penetration of the paste 5, bleeding occurs in the printed conductor pattern.

This type of printing smear is likely to occur in conductor patterns that run perpendicular to the squeegee movement direction, so the principle of pattern design is to avoid creating conductor patterns that run perpendicular to the squeegee movement direction. As explained below, it is often impossible to completely adhere to this principle.

FIG. 12 illustrates a pattern layout in a conventional metal screen. In this diagram,
15 is a metal mask, 7 and 7' are mask patterns for dicing reference lines, 8 and 8' are mask patterns for lead attachment pads, 9 are mask patterns for die bond patterns, and 10 are mask patterns for wire bond pads. It is.

When printed using this metal screen 15, the conductor patterns that cause noticeable bleeding are the dicing reference line 7 perpendicular to the moving direction X of the squeegee 6, and the die bond pattern mask pattern 9.
A wire bond pad 10 and a lead attaching pad 8 are perpendicular to the squeegee movement direction X and are located on the respective extension lines of the upper edge and lower edge of the squeegee.
The reason why the lead attachment pad 8 tends to bleed is due to the bending of the stainless steel mesh in the portion of the dicing reference line mask pattern 7 that is printed immediately before it.

In particular, for the wire bond pad 10, it is difficult to obtain a minimum conductor spacing, and sharp edges are required for automatic pattern recognition during wire bonding, so print bleeding must be strictly suppressed.

[Purpose of the invention]

An object of the present invention is to provide a metal screen for printing conductor patterns that reduces printing bleed of wire bond pads and other conductor patterns, and can be used for printing conductor patterns continuously more times than before. It is in.

[Summary of the invention]

The present invention provides a mask for wire bond pads around a mask pattern for die bond patterns in a metal screen for printing conductor patterns such as die bond patterns and wire bond pads on green sheets of substrates for hybrid modules. Among the pattern groups, those in the direction perpendicular to the squeegee movement direction are arranged at a position at least a certain distance away from the first and last printed edge parts of the mask pattern for the die bond pattern in the squeegee movement direction, This prevents printing smudges on wire bond pads, which are most disliked, and thereby increases the number of times that metal screens can be continuously printed.

Further, in a preferred embodiment of the present invention, the mask pattern for the dicing reference line is formed in a broken line shape, and the mask pattern for the die bond pattern has its corners cut or rounded, or has a pentagonal or more shape. Formed into a polygonal shape.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a mask pattern for a portion of a metal screen in an embodiment of the present invention. In this figure, 20 is a mask pattern for a die bond pattern, and 21 is a mask pattern for a wire bond pad. A large number of wire bond pad mask patterns 21 are arranged so as to surround the die bond pattern mask pattern 20, but only some are shown in the figure. X is the squeegee movement direction.

Among the plurality of mask patterns 21 for wire bond pads, a mask pattern 21a running perpendicular to the squeegee movement direction (i.e., one in a direction perpendicular to the squeegee movement direction) is located at the upper edge of the die bond pattern mask pattern 20. It is placed at a position offset from the extension line 22 by about 0.2 mm (the larger this is, the more securely the printing bleed will be prevented).
Further, a portion of the mask pattern 21b adjacent above the mask pattern 21a, which is perpendicular to the squeegee movement direction X, is also separated from the extension line 22 by about 0.2 mm.
Although not shown in the figure, the same applies to the wire bond pad mask pattern 21 near the upper right corner of the die bond pattern mask pattern 20. Furthermore, although not shown in the figure, the mask pattern 21 for the wire bond pad, which exists near the extension line 23 of the lower edge of the mask pattern 20 for the die bond pattern, is similar to the mask patterns 21a and 21b described above. Extension line 23 to
It is formed approximately 0.2mm apart from the Further, the length of the mask pattern including the mask pattern 21 in the direction perpendicular to the squeegee movement direction X is determined to be one-tenth or less of the print area length.

According to the metal screen of this example, when the metal mask thickness is 30 μm and the printing thickness is 20 μm, it has been experimentally shown that the bleeding of all wire bond pads can be kept below the allowable limit even after continuous printing up to 10 times. has been confirmed.

Note that there may be cases where the mask patterns 21 for wire bond pads cannot be arranged as described above. In that case, all of the mask patterns 21,
Alternatively, at least the area near the edge extension line of the die-bonding pattern mask pattern 20 may be formed as a pattern inclined with respect to the squeegee moving direction X.

In the metal screen according to the present invention, mask patterns for wire bond pads are arranged as in the above embodiment, but more preferably, masks for conductor patterns such as dicing reference lines and dummy lines in a direction perpendicular to the direction of squeegee movement. The pattern is formed in the shape of a broken line. FIG. 2 shows an example of a mask pattern such as a dicing reference line formed in this manner. If the ratio B/A of the length A of the printed part (opening) and the length B of the non-printed part of this mask pattern is selected in the range of 1/2 to 1/10, it generally prevents bleeding in printing such as dicing standards. Can be effectively prevented.

In the above embodiment, the corners of the die-bonding pattern mask pattern 20 were at right angles, but as shown in FIG. As shown in the figure, it is generally preferable that the overall shape of the die-bonding pattern mask pattern 20 is a polygon with five or more sides. In this way, the bending of the stainless steel mesh by the squeegee at the edge portion of the mask pattern 20 for the die bond pattern gradually progresses, so that printing bleeding of the wire bond pad can be further reduced.

As shown in FIG. 5, the printing device is designed so that the inclination angle of the squeegee 6 with respect to the perpendicular line of the squeegee movement direction If the setting is set to , it is possible to suppress bending of the stainless steel mesh in the portion of the conductor pattern 24 in the direction perpendicular to the squeegee movement direction X, which is effective in preventing printing smearing.

Note that the material of the mesh of the metal screen of the present invention is not limited to stainless steel.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, it is possible to significantly reduce the printing smear of the wirebond pad around the die bond pattern, to print a sharp wirebond pad, and to reduce the printing smearing. By reducing this, it is possible to increase the number of times that metal screens can be printed continuously and improve printing efficiency.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a mask pattern for a die bond pattern and a mask pattern for a wire bond pad in a metal screen according to the present invention, and FIG. 2 is a mask pattern for dicing reference lines, etc. in a metal screen according to the present invention. 3 and 4 are plan views showing modified examples of the mask pattern for the die bond pattern, FIG. 5 is an explanatory diagram regarding the angle of the squeegee, and FIG. 6 is a board for hybrid module. 7 is a schematic sectional view of a printing screen consisting of a stainless steel mesh and a mask made of photosensitive emulsion. FIG. 8 is a schematic sectional view showing the general structure of a metal screen. 9. The figure is a graph showing the relationship between the metal mask thickness and the printing thickness in a metal screen. Figure 10 is a graph showing the relationship between the number of continuous printings possible with a conventional metal screen and the metal thickness. Figure 11 is a conductor pattern using a metal screen. FIG. 12 is a schematic cross-sectional view for explaining the printing direction and the cause of printing blur, and FIG. 12 is a plan view showing an example of a mask pattern in a conventional metal screen. 20...Mask pattern for die bond pattern, 21, 21a, 21b...Mask pattern for wire bond pad, 22, 23...Extension line of mask pattern 20, X...Squeegee movement direction.

Claims (1)

[Claims] 1. Die bond pattern, wire bond pattern, etc. on the green sheet of the hybrid module substrate, etc.
In a metal screen for printing conductor patterns such as pads, among the mask patterns for wire bond pads around the mask pattern for die bond patterns, the pattern in the direction perpendicular to the squeegee movement direction is the mask pattern for the die bond pattern. 1. A metal screen for printing a conductor pattern, characterized in that the metal screen is located a certain distance or more away from the first and last edge portions printed on the screen in the direction of movement of the squeegee. 2. The metal screen for printing a conductor pattern according to claim 1, wherein the mask pattern for the conductor pattern, such as the dicing reference line perpendicular to the squeegee movement direction, is formed in the shape of a broken line. 3 The mask pattern for the die bond pattern is
2. The metal screen for printing a conductor pattern according to claim 1, wherein the corner portions are cut or rounded. 4 Mask pattern for die bond pattern is 5
2. The metal screen for printing a conductive pattern according to claim 1, wherein the metal screen is formed into a polygon having a shape larger than a square.