JPH0194697A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To allow a multilayer wiring board to have high connection reliability without improving manufacturing accuracy which would directly reduce costs by forming a conductive throughhole extending between the inner conductive layers together with a throughhole extending through the board in the multilayer printed wiring board having more than two inner conductive layers. CONSTITUTION:A multilayer printed wiring board 2' having more than two inner conductive layers, wherein a conductive throughhole 4 extending between the inner conductive layers 1 is formed together with a throughhole 3 extending through the board. For example, the multilayer printed wiring board 2' having two inner conductive layers 1, wherein a conductive pattern 5 which connects the throughhole 3 extending through the board and the inner layer throughhole 4 is formed, so that an electric signal is allowed to pass through the throughhole 3 extending through the board as well as the inner layer throughhole 4 via the conductive pattern 5. According to the constitution, even when connection reliability of the throughhole extending through the board is deteriorated due to variations in manufacturing accuracy, its reliability as a conductive path can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printed wiring board, and particularly to a multilayer printed wiring board having two or more inner layers.

[Conventional technology]

In recent years, the density of multilayer printed wiring boards has increased significantly, and highly multilayer printed wiring boards having 20 or more conductor layers have appeared. In this case, while the plate thickness inevitably becomes thicker, the through-hole diameter becomes smaller in order to ensure sufficient wiring accommodation.For example, an aspect ratio of 4.0'/"0.4=10 or more is required. On the other hand, as the aspect ratio increases, it becomes difficult to drill through-holes with a drill, so step drilling methods and front-back processing methods have been devised and put into practical use.

FIG. 2 is a side view of a conventional multilayer printed wiring board 2, in which front and back through holes 3 are provided in the multilayer printed wiring board 2 on which internal conductor layers 1 are laminated.

[Problem that the invention seeks to solve]

However, as shown in FIG.
In the multilayer printed wiring board 2 formed by laminating layers, the inner walls of the front and back penetrating through holes 3 after processing may be affected by errors in the drilling position and drill diameter accuracy during through hole processing using the step drilling method or the front and back processing methods. There is a step in the
This had the disadvantage that the connection reliability of the plating after through-hole plating deteriorated.

For example, in the case of a printed wiring board made of polyimide material with a board thickness of 6.0 mm, if the front and back sides are processed with a hole diameter of 0.35 mm,
In the connection reliability test specified in MIL-FTQ-107, an increase in connection resistance was observed after 20 cycles of application, and as shown in Figure 3, connection failures began to occur after 40 cycles of application, and after that, failures rapidly occurred. It tends to increase. Also,
As a result of cross-sectional observation of these connection failures, it was revealed that barrel cracks in the T/H plating occurred at the step portions that occur during hole drilling.

In contrast to the above-mentioned conventional multilayer printed wiring board, the present invention has an original content in that a multilayer printed wiring board having high connection reliability can be obtained without improving manufacturing accuracy which would lead to an increase in cost.

[Means for solving problems]

The present invention is characterized in that, in a multilayer printed wiring board having two or more inner conductor layers, conductive through holes are provided between the inner conductor layers in parallel with the front and back through holes.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of one embodiment of the present invention.

In a multilayer printed wiring board 2' having two inner conductor layers 1, a conductor pattern 5 is provided to connect front and back through holes 3 and inner layer through holes 4. The electrical signal passes through the front and back through holes 3 and at the same time passes through the inner layer through holes 4 via the conductor pattern 5.

As for the connection reliability of the multilayer printed wiring board made of polyimide material with a board thickness of 6.0 mm according to this example having such a structure, the results of the above-mentioned MIL method test showed that there were no connection failures up to 200 cycles as shown in Figure 2. I got the result.

〔Effect of the invention〕

As explained above, the present invention provides a conductive path via an inner layer through-hole in the middle of the front and back through-holes, so that even if the connection reliability of the front and back through-holes deteriorates due to variations in manufacturing precision, the conductive path This has the effect of maintaining reliability as a route.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a multilayer printed wiring board according to an embodiment of the present invention, FIG. 2 is a sectional view showing the structure of a conventional multilayer printed wiring board, and FIG. 3 is similar to FIG. 1. 3 is a graph showing the results of comparing the connection reliability of the example shown in FIG. 2 and the conventional multilayer printed wiring board shown in FIG. 2 according to the MIL-3TD-107 method. 1... Inner conductor layer, 2.2'... Multilayer printed wiring board,
3... Front and back through holes, 4... Inner layer through holes, 5... Conductor pattern.

Claims (1)

[Claims] A multilayer printed wiring board having two or more inner conductor layers, characterized in that a conductive through-hole is provided between the inner conductor layers in parallel with the front and back through-holes.