JPH0426800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a multilayer printed wiring board used in various electronic devices and used to mount electronic components.

(Prior art) In general, printed wiring boards are designed based on the standard for electronic components, which assumes a matrix-like lattice with a fixed interval called a basic lattice (usually 2.54 mm) and an auxiliary lattice that divides the lattice into equal parts. Through-holes are provided at grid positions to mount electronic components such as ICs, and necessary wiring is provided at auxiliary grid positions. As electronic devices have become more sophisticated in recent years, there has been an increasing demand for higher density in multilayer printed wiring boards. Unused via holes are commonly used.

This via hole for non-component mounting is provided in an auxiliary grid position different from the basic grid, so in order not to interfere with wiring at other auxiliary grid positions, the diameter is smaller than that of the through hole for component mounting. Therefore, the cutting resistance during drilling of this via hole is greater than that of a through hole for mounting components, resulting in a decrease in machinability. This is because machinability generally decreases as the diameter of the through hole becomes smaller.

Around the through-hole connection portion of the inner layer pattern, the outer layer base material and the inner layer pattern peel off due to cutting resistance during drilling, although there are differences in degree. The degree of this peeling increases as the machinability decreases. Therefore, in a via hole with a small diameter, the peeling is more likely to occur than in a through hole for mounting components due to decreased machinability.

In particular, when a micro-diameter via hole penetrates a wide pattern (usually called a solid pattern) such as an inner layer power supply pattern or an inner layer ground pattern and is connected in an inner layer, the The adhesion between the prepreg serving as the outer layer base material and the inner layer pattern is weak, and the peeling is likely to occur. This difference in adhesion is because in the latter case, the prepreg adheres more strongly to the exposed resin part of the base material around the land pattern than to the copper surface of the inner layer base material. This is due to the fact that it improves

By the way, the reason why the prepreg adheres more strongly to the base resin part than to the copper surface of the inner layer base material is as follows. Physically, since electrolytic copper foil is generally used as the copper foil for the base material, the resin part of the base material exposed by removing the copper foil is rougher than the copper surface that has been subjected to treatments such as polishing and oxidation. It has a very high level of respectability. From a chemical standpoint, the adhesion between resins is considerably stronger than the adhesion between resin and copper (copper oxide).

The peeling appears as an appearance defect called haloing. This haloing is a common method in which an oxide film is formed on the copper surface of the base material in order to improve the adhesion strength when the copper surface of the base material and the prepreg are brought into close contact with each other in the manufacturing process of multilayer printed wiring boards. However, in this method, if peeling occurs between the outer layer base material and the inner layer pattern around the through-hole connection part of the inner layer pattern, and acid etc. seeps in between, the oxide film may partially dissolve. This is an external defect in which the area looks white, but this occurs due to deterioration of insulation resistance.
This may cause defects such as increased peeling between the outer layer substrate and the inner layer pattern, and cracks in through-hole plating.

Conventionally, no measures have been taken to deal with only the haloing that occurs around the connection portion of the inner layer solid pattern to the via hole. To explain this conventional situation with reference to FIGS. 7 and 8, the via hole 22 for non-component mounting formed at the auxiliary grid position on the board surface has no boundary with the inner layer pattern 24, which is a solid pattern. They are directly and completely connected. In other words, the multilayer printed wiring board 21 does not have a pattern missing part around the connection part 27, and no measures were taken to prevent separation between the inner layer pattern 24 and the outer layer base material 29 around the connection part 27. be.

(Problems to be solved by the invention) The present invention has been made in view of the above-mentioned circumstances.
The problem to be solved is the occurrence of haloing around the connection portion of the inner layer solid pattern to the via hole located at the auxiliary grid position on the substrate surface.

An object of the present invention is to improve the adhesion between the inner layer pattern and the prepreg serving as the outer layer base material around the connection portion of the inner layer solid pattern to the via hole for non-component mounting located at the auxiliary grid position on the board surface. The object of the present invention is to provide a multilayer printed wiring board in which the occurrence of haloing around the connection portion is suppressed.

(Means for Solving the Problems) The means adopted by the present invention to solve the above problems is to install via holes with a hole diameter of 0.7 mm or less that are not used for component mounting at the auxiliary grid positions on the board surface. is formed,
A multilayer printed wiring board in which an inner layer land portion is formed in the via hole and an inner layer pattern is formed around the inner layer land portion on the same layer, and the inner layer land portion and the inner layer pattern surrounding the inner layer land portion are connected to each other. In between, two or more connection patterns are left to electrically connect them, forming a pattern missing part, and the distance between the inner layer land and the surrounding inner layer pattern is equal to or less than the basic lattice spacing. This is a multilayer printed wiring board featuring:

This means of the invention will now be explained in more detail with reference to FIGS. 1 and 2. FIG.

FIG. 1 shows one of the multilayer printed wiring boards according to the present invention.
FIG. 2 is a cross-sectional view of the - line portion in FIG. 1. The multilayer printed wiring board 1 shown in FIG. Inner layer pattern 4 in which via hole 2 for non-component mounting is a solid pattern
and its inner layer pattern 4
This is characterized in that a pattern missing portion 3 is formed around a connecting portion 7 between the via hole 2 and the via hole 2. The pattern missing portion 3 of this multilayer printed wiring board 1 has a shape that allows the formation of an inner layer land portion 6 and a connection pattern 5 that electrically connects this inner layer land portion 6 and the inner layer pattern 4, In addition, the width of the pattern missing portion 3, that is, the distance between the inner layer land portion 6 and the inner layer pattern 4, is
For example, the lattice spacing is set to be equal to or less than the basic lattice spacing. In addition to the fan-shaped shape shown in FIG. 3, the specific shape of the pattern missing portion 3 may be a fan shape as shown in FIG. 4 or FIG. Various shapes such as a fan shape and the shape shown in FIG. 6 in which the shape of the pattern missing portion 3 in FIG. 5 is changed are effective. Further, the diameter of the via hole 2 is, for example, 0.5 mm or less.

(Actions of the Invention) By adopting the above-described measures, the present invention has the following effects.

In the pattern missing part 3 formed around the connection part 7 between the inner layer pattern 4, which is a solid pattern, and the via hole 2 for non-component mounting formed at the auxiliary grid position on the board surface, the prepreg 9a and the exposed base material As described in the (prior art) section, the resin portion 10a adheres more strongly than the prepreg 9a and the inner layer pattern 4, so this strong adhesion improves the adhesion between the prepreg 9a and the inner layer land portion 6. This prevents peeling between the outer layer base material 9 and the inner layer land portion 6 formed by curing the prepreg 9a, and suppresses haloing.

Especially when the hole diameter of via hole 2 is 0.5 mm or less,
The measures taken by the present invention have a remarkable effect and suppress haloing.

Furthermore, since the distance between the inner layer land portion 6 and the inner layer pattern 4 is equal to or less than the basic lattice spacing, the shielding effect of the inner layer pattern 4 does not deteriorate.

Furthermore, since the connection patterns 5 are formed at at least two locations, the reliability of the electrical connection between the via hole 2 and the inner layer pattern 4 will not deteriorate due to hole misalignment or the like.

Next, the present invention will be explained in detail using examples.

(Example) Example 1 The multilayer printed wiring board 1 has an 8-layer structure in which a power supply pattern or a ground pattern, each of which is a solid pattern, is provided on the second and seventh layers, and the solid pattern portion is provided with an auxiliary pattern on the board surface. Of the via holes 2 for non-component mounting with a hole diameter of 0.4 mm in the grid.
Sixty-four holes were connected, and the pattern missing part 3 shown in FIG. 3 was formed around the connection part 7 with the via hole 2 of the solid pattern part. The multilayer printed wiring board 1 thus produced was evaluated for haloing of the 264 via holes. The evaluation was performed by polishing and removing the patterns of the first and eighth layers and a part of the outer layer base material 9 between the first and second layers and between the seventh and eighth layers.
The width (distance from the connection part) of the haloing generated around the connection part 7 with the via hole 2 of the second layer power supply pattern and the seventh layer ground pattern was measured using a 100x microscope.

As a result, haloing with a width of 0.05 mm or more and less than 0.1 mm occurred at eight locations, and no haloing with a width of 0.1 mm or more occurred.

Example 2 In Example 1, the hole diameter of via hole 2 was
It was set to 0.7mm. The thus produced multilayer printed wiring board 1 was evaluated for haloing in the same manner as in Example 1. As a result, the width is 0.05mm or more, 0.1
Haloing of less than mm occurred in 3 places,
No haloing of 0.1 mm or more occurred.

Example 3 In Example 1, the pattern missing portion 3 had the shape shown in FIG. The thus produced multilayer printed wiring board 1 was evaluated for haloing in the same manner as in Example 1. As a result, five haloings with a width of 0.05 mm or more and less than 0.1 mm occurred, and no haloing with a width of 0.1 mm or more occurred.

Comparative Example 1 In Example 1, the pattern missing portion 3 was not formed. The thus produced multilayer printed wiring board 21 was evaluated for haloing in the same manner as in Example 1. As a result, the width is 0.05mm or more, 0.1mm
There were 28 places where haloing was less than 0.1mm, and 5 places where haloing was more than 0.1mm.

(Effects of the Invention) As detailed above, in the present invention, as exemplified in each of the above embodiments, holes with a diameter of 0.7 mm or less that are not used for component mounting and are formed at the auxiliary grid positions on the board surface. via hole 2
In the multilayer printed wiring board 1 to be connected to the inner layer pattern 4 which is a solid pattern, two or more connection patterns 5 are left around the connection portion 7 of the inner layer pattern 4 to the via hole 2, and the pattern missing portion 3 is removed.
It is characterized in that the distance between the inner layer land portion 6 and the inner layer pattern 4 surrounding it is equal to or less than the basic lattice spacing. Since the base material resin portion 10a, which becomes the base material 10, is strongly adhered, the adhesion between the prepreg 9a and the inner layer land portion 6 is improved, and peeling between the outer layer base material 9 and the inner layer land portion 6 is less likely to occur, and the halo This makes it possible to suppress the occurrence of ing.

Further, according to the multilayer printed wiring board 1 of the present invention, since the distance between the inner layer land portion 6 and the inner layer pattern 4 is equal to or less than the basic lattice spacing, the shielding effect etc. of the inner layer pattern 4 does not deteriorate.
Since the connection pattern 5 is formed in at least two locations, the reliability of the electrical connection between the via hole 2 and the inner layer pattern 4 does not deteriorate due to hole misalignment or the like.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a partially cut away part of a multilayer printed wiring board according to the present invention, and FIG.
The cross-sectional views taken along the - line in the figure, Figures 3 to 6, are as follows:
FIG. 2 is a plan view showing a pattern missing portion in the X portion of FIG. 1; Figure 7 shows one of the conventional multilayer printed wiring boards.
FIG. 8 is a perspective view of a cutaway portion, and FIG. 8 is a sectional view of the − portion in FIG. 7 corresponding to FIG. 2. Explanation of symbols, 1...Multilayer printed wiring board, 2...
... Via hole, 3 ... Pattern missing part, 4 ...
Inner layer pattern (connected to via hole 2), 5
... Connection pattern, 6 ... Inner layer land part, 7 ...
Connection part, 8... (does not connect with via hole 2)
Inner layer pattern, 9... Outer layer base material, 10... Inner layer base material.

Claims (1)

[Claims] 1. A via hole with a hole diameter of 0.7 mm or less, which is not used for component mounting, is formed at the auxiliary grid position on the board surface, and an inner layer land portion is formed in this via hole. A multilayer printed wiring board in which an inner layer pattern is formed around the same layer on the same layer, and there are two or more connections between the inner layer land portion and the surrounding inner layer pattern to electrically connect them. What is claimed is: 1. A multilayer printed wiring board, characterized in that a pattern is left behind and a pattern missing portion is formed, and a distance between the inner layer land portion and the inner layer pattern surrounding the inner layer land portion is equal to or less than a basic lattice spacing.