JPS5898997A - Flexible 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 The present invention relates to a flexible printed circuit board that is particularly suitable for use as a substrate for lead wiring of thin-film magnetic heads.Thin-film magnetic heads have an extremely small core area, which causes crosstalk between adjacent track beds. It is superior to conventional bulkheads in that it is very small and does not require shielding between tracks. However, on the other hand, if many signal lines from each track of the head are not properly drawn out, crosstalk between adjacent tracks will occur at the drawn-out portion. However, as thin-film magnetic heads are made to have narrower tracks and become multi-track, it becomes necessary to draw out a large number of signal lines from one head chip, and it is difficult to draw out these lines with high precision.

For this reason, the wiring method in which two lead wires are provided for each track is undesirable because the number of lead wires is large, and therefore, in reality, one wire of each track is grounded and a common single wire is used to lead out the wires. A wiring method that performs this is adopted. Figure 1 shows the conventional wiring method.
Figure (a) is a plan view, and figure (bl is a side sectional view taken along line AA').

1 is a flexible printed circuit (FPC), 2 is an insulating layer, 3 is a plurality of track signal lines formed on the insulating layer, and 4 ground lines.

The head 5 is connected to one of the track signal lines and the ground line.

However, in the conventional wiring method described above, the following phenomenon occurs. That is, the signal current flowing in a track line that is distant from the ground line forms a large current loop, and the farther the track line is from the ground line, the more electromagnetic induction caused by the current loop cannot be ignored.

This phenomenon of electromagnetic induction is a serious problem because it induces crosstalk between tracks.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a wiring board that can prevent tarostalk between tracks and also enable good wiring of signal lines for a high-density thin-film magnetic head. purpose.

Hereinafter, one embodiment of a flexible printed circuit board according to the present invention will be described in detail using the drawings.

FIG. 2 shows an embodiment of the flexible printed circuit board according to the present invention.
FIG. 3 is a side sectional view taken along line B'. Signal lines 3 for all tracks are formed on one side of the insulating layer 2, and ground lines 4 are formed on the other side. The ground line 4 has a position and area that covers all of the signal lines 3 of all the tracks. 5
This is a thin film magnetic head for recording. The signal current flows through the signal line 3 on the front side to the head 5 and exits to the ground line 4 on the back side.

According to this configuration, the loop formed by the signal current has an area as narrow as the thickness of the insulating layer 2 (approximately 50μ) multiplied by the length of the FPC, and the current loop flowing through the signal line 3 of each track is each on a different plane. Therefore, the mutual electromagnetic induction between the signal lines of each track becomes sufficiently small.

According to experiments, when comparing a multi-channel head using a flexible printed circuit board with the configuration of the above embodiment and a conventional multi-channel head using a conventional flexible printed circuit board with the configuration shown in FIG. −
Crosstalk between signal lines of about 20 dB was observed,
It has been found that in a multi-channel head using a 7-lexiple printed circuit board configured according to the embodiment of the present invention, the crosstalk between signal lines is reduced to about -50 dB or less, and there is no problem in practical use.

In the above example, an FPC was shown in which a signal line and a ground line were formed on the front and back sides of the insulating layer 2, respectively. Of course, it is also possible to attach it to a two-layer structure substrate.

As described above in detail, according to the present invention, the tallostoke of mutual signal lines can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 shows a conventional flexible printed circuit board; FIG. 1(a) is a plan view, FIG. at is a plan view, and the same figure (bl is a side sectional view. In the figure, 1: flexible printed circuit, 2: insulating layer, 3 Nidrac signal line, 4 Nigelland wire, 5:
head. Agent Patent Attorney Aihiko Fukushi

Claims (1)

[Claims] ], a multi-track signal line is arranged on one side of the insulating layer, a common ground line is arranged on the other side, and the common ground line is set at a position and in an area that substantially covers all of the multi-track signal lines. A flexible printed circuit board characterized by: