JPH04320092A - Multilayer printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed circuit board having blind through holes formed therein.

0002

[Prior Art] Recently, with the increasing density of printed circuit boards,
The area occupied by through holes can no longer be ignored, and it has become necessary to make them blind.

[0003] As a conventional method for forming a multilayer printed circuit board having blind through holes, first, as shown in FIG. )12a-12c
After preparing a multilayer printed circuit board B laminated through the multilayer printed circuit board B and etching away a part of the copper foil 11a formed on the uppermost layer of the multilayer printed circuit board B, the insulating base material 1 of the lower layer is removed.
Holes 13 are formed in 2a by, for example, sandblasting with silicon carbide particles. In this sandblasting process, the lower layer copper foil 11b is not removed, so the hole 13 formed by this process becomes a blind through hole 13 whose bottom is closed with the lower layer copper foil 11b.

Next, as shown in FIG. 4B, copper plating layers 14 are formed on the upper and lower surfaces of the multilayer printed circuit board B by performing electroless plating and copper plating. At this time,
There is also a copper plating layer 14 inside the blind through hole 13.
is formed, so that the copper foil 11a of the uppermost layer and the copper foil 11b of the lower layer are electrically connected by this copper plating layer 14. In this way, the blind through hole 13
A multilayer printed circuit board B is obtained.

[0005]

[Problems to be Solved by the Invention] However, in the conventional multilayer printed circuit board B, as the density of the printed circuit board increases, the diameter of the blind through hole 13 becomes smaller, and the connection area with the copper foil 11b becomes smaller. In this case, the adhesion strength between the copper foil 11b and the copper plating layer 14 decreases, and the copper foil 11b and the copper plating layer 14 are easily peeled off due to thermal stress caused by subsequent soldering, etc., resulting in a problem of circuit disconnection.

That is, in the conventional multilayer printed circuit board B,
If heat is applied during soldering, the insulating base material (e.g. 1
2a) thermally expands, but copper foil (for example, 11b) generally has a smaller coefficient of thermal expansion than the insulating base material 12a, so at the interface a between the copper plating layer 14 and the copper foil 11b, A force acts to peel off the copper foil 11b along the thickness direction of the insulating base material 12a. In the illustrated example, the copper is joined to each other at the interface a, but in reality, the structure is such that copper is deposited on the copper foil 11b by copper plating treatment, so the diameter of the blind through hole 13 is set as above. When the connection area becomes very small, the copper plating layer 14 easily peels off from the copper foil 11b, which is disadvantageous in that a disconnection accident at the interface a is likely to occur.

[0007] The present invention was made in view of these problems, and its purpose is to reduce the diameter of the blind through hole and reduce the connection area between the copper plating layer and the copper foil. However, it is an object of the present invention to provide a multilayer printed circuit board that can prevent the peeling of the copper plating layer from the copper foil due to thermal stress such as soldering.

[0008]

[Means for Solving the Problems] The present invention provides a plurality of conductor layers 1a to 1d that are laminated via insulating base materials 2a to 2c, respectively, and an upper layer of the plurality of conductor layers 1a to 1d. It has a blind through hole 3 that penetrates from the conductor layer 1a to the conductor layer 1b below it, and the metal plating layer 6 formed including the blind through hole 3 allows the upper conductor layer 1a and the lower conductor layer 1b to be connected to each other. In the electrically connected multilayer printed circuit board A, the metal plating layer 6 is formed in the shape of a flange along the lower conductor layer 1b at the bottom of the blind through hole 3, so that the metal plating layer 6 is electrically connected to the lower conductor layer 1b. Connect to and configure.

[0009]

[Operation] According to the structure of the present invention described above, the metal plating layer 6
is formed in the shape of a flange along the lower conductor layer 1b at the bottom of the blind through hole 3 to electrically connect with the lower conductor layer 1b. The removed portion 6a functions as a kind of locking part, and the insulating base material 2a is peeled off in the thickness direction due to thermal stress during soldering etc. caused by the difference in thermal expansion coefficient between the insulating base material 2a and the metal. The force can be dispersed to the insulating base material 2a side via the flange-shaped portion 6a.

Therefore, for example, blind through hole 3
The diameter of the metal plating layer 6 and the lower conductor layer 1 become smaller.
Even if the connection area with b becomes smaller, it is possible to prevent the peeling phenomenon of the metal plating layer 6 from the lower conductor layer 1b due to thermal stress such as soldering, and reduce disconnection defects in the multilayer printed circuit board A. Furthermore, it is possible to improve the yield.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a process diagram showing the structure of a multilayer printed circuit board A according to this embodiment according to its manufacturing process. The steps will be explained below.

First, as shown in FIG. 1A, a plurality of copper foils 1
A multilayer printed circuit board A in which a to 1d are laminated via insulating substrates (e.g., glass-epoxy resin substrates) 2a to 2c is prepared, and a copper foil formed on the top layer of the multilayer printed circuit board A is prepared. After a portion of 1a is removed by etching, holes 3 are formed in the underlying insulating base material 2a by, for example, sandblasting with silicon carbide particles. Since the lower copper foil 1b is not removed in this sandblasting process, the hole 3 formed by this process becomes a blind through hole 3 whose bottom is closed with the lower copper foil 1b.

Next, as shown in FIG. 1B, the upper layer copper foil 1
After forming a resist mask 4 having openings 4a at locations corresponding to the blind through holes 3, an isotropic wet etching process (multilayer The surface of the lower copper foil 1b exposed from the blind through hole 3 is etched away by immersing the printed circuit board in the etching solution. Since the above etching process is isotropic etching using an etching solution, the copper foil 1b is etched not only on the surface exposed from the blind through hole 3 but also in the lateral direction (side etching), and at the bottom of the blind through hole 3. A cavity 5 is formed which extends laterally. Although not shown in FIG. 1A, a mask is used to drill the blind through holes 3 by sandblasting, but if this mask is resistant to the etching solution, it can also be used as the resist mask 4. Good too.

Thereafter, as shown in FIG. 1C, electroless plating and copper plating are performed to form the multilayer printed circuit board A.
By forming a copper plating layer 6 on the upper and lower surfaces of
A multilayer printed circuit board A according to this example in which blind through holes 3 are processed to be electrically conductive is obtained. At this time, since the copper plating layer 6 is also formed inside the blind through hole 3,
This copper plating layer 6 electrically connects the uppermost copper foil 1a and the lower copper foil 1b. Further, this copper plating layer 6 is formed in a flange shape so as to fill the cavity 5 formed at the bottom of the blind through hole 3. In this case, the flange-shaped portion 6a of the copper plating layer is sandwiched between the insulating base material 2a and the lower copper foil 1b.

As mentioned above, according to this example, the copper plating layer 6
is formed in a flange shape along the lower layer copper foil 1b at the bottom of the blind through hole 3, so that the lower layer copper foil 1b
Since it is electrically connected to the copper plating layer 6,
The flange-shaped portion 6a functions as a kind of locking part, and the insulating base material 2a is protected against heat stress caused by soldering etc. due to the difference in thermal expansion coefficient between the insulating base material 2a and copper.
The peeling force in the thickness direction can be dispersed to the insulating base material 2a side via the flange-shaped portion 6a.

Therefore, for example, blind through hole 3
Even if the connecting area between the copper plating layer 6 and the copper foil 1b becomes smaller due to the smaller diameter, it is possible to prevent the peeling phenomenon of the copper plating layer 6 from the copper foil 1b due to heat stress such as soldering. Therefore, it is possible to reduce disconnection defects in the multilayer printed circuit board A and improve yield.

In the above embodiment, when isotropically etching the lower copper foil 1b, only the surface portion thereof is etched away to form a cavity 5 extending laterally at the bottom of the blind through hole 3. However, as shown in FIG. 2A, after drilling the blind through hole 3 by sandblasting, the blind through hole 3 is
The exposed copper foil 1b may be removed by etching down to the underlying insulating base material 2b.

In this case as well, side etching of the copper foil 1b progresses in the lateral direction, and a cavity 5 extending in the lateral direction is formed at the bottom of the blind through hole 3. After that,
As shown in FIG. 2B, a copper plating layer 6 is formed on the upper and lower surfaces of the multilayer printed circuit board A by electroless plating and copper plating, and the upper layer copper foil 1a and the lower layer copper foil 1b are separated. Connect electrically. At this time, the copper plating layer 6 embedded in the cavity 5 is formed into a flange shape, and the flange portion 6a is sandwiched between the two insulating base materials 2a and 2b. effect can be obtained.

In addition, when forming the blind through hole 3 mechanically with a drill instead of using sandblasting, as shown in FIG. A blind through hole 3 is formed by mechanically drilling a hole beyond the first layer insulating base material 2a to a part of the second layer insulating base material 2b, as shown in FIG. 3B. Wet etching is performed using the above etching solution to laterally etch back the copper foil 1b exposed from the inner surface of the blind through hole 3.

This etch-back process forms a cavity 5 that extends laterally at the bottom of the blind through hole 3. After that, as shown in FIG. 3C, electroless plating and copper plating are performed to form a copper plating layer 6 on the top and bottom surfaces of the multilayer printed circuit board A.
The upper layer copper foil 1a and the lower layer copper foil 1b are electrically connected. At this time, the copper plating layer 6 embedded in the cavity 5 is formed into a flange shape, and the flange portion 6a is sandwiched between the two insulating base materials 2a and 2b. effect can be obtained.

[0021]

[Effects of the Invention] According to the multilayer printed circuit board according to the present invention, even if the diameter of the blind through hole becomes smaller and the connection area between the metal plating layer and the lower conductor layer becomes smaller, it is possible to reduce the heat resistance caused by soldering etc. It is possible to prevent the peeling phenomenon of the metal plating layer from the underlying conductor layer due to stress, and it is possible to improve the reliability and yield of the multilayer printed circuit board.

[Brief explanation of drawings]

FIG. 1 is a process diagram illustrating the structure of a multilayer printed circuit board according to the present embodiment according to its manufacturing process.

FIG. 2 is a process diagram showing the structure of a multilayer printed circuit board according to a modification of the present embodiment according to its manufacturing process.

FIG. 3 is a process diagram showing the structure of a multilayer printed circuit board according to another modification of the present embodiment according to its manufacturing process.

FIG. 4 is a process diagram showing the structure of a conventional multilayer printed circuit board according to its manufacturing process.

[Explanation of symbols]

A Multilayer printed circuit board 1a-1d Copper foil 2a-2c Insulating base material 3 Blind through hole 4 Resist mask 5 Cavity 6 Copper plating layer 6a Flange-shaped part

Claims (1)

[Claims] Claim 1: A plurality of conductor layers are each laminated with an insulating base material interposed therebetween, and a blind through hole is provided that penetrates from an upper conductor layer to a lower conductor layer among the plurality of conductor layers. , in a multilayer printed circuit board in which the upper conductor layer and the lower conductor layer are electrically connected by a metal plating layer formed including the blind through hole, the metal plating layer is formed in the blind through hole. A multilayer printed circuit board, characterized in that the bottom portion is formed in a flange shape along the lower conductor layer and is electrically connected to the lower conductor layer.