JPH04188886A - Printed wiring board - Google Patents

Abstract

PURPOSE:To protect a printed wiring board against warpage caused by thermal expansion by a method wherein a dummy pattern composed of wires extend in the same direction with a wiring is provided to an empty space area of the other side of the printed board opposite to its side where a conductor circuit is provided. CONSTITUTION:As a dummy pattern 5 is composed of straight patterns 5a arranged in the same wiring direction with a conductor circuit 2 formed on a side B of a printed wiring board 1, the warpage of the board 1 due to the circuit 2 by heating is canceled by the dummy pattern 5, and a warping action is prevented from occurring newly, so that the board 1 can be surely protected against warpage. The patterns 5a are enhanced or lessened in size and number corresponding to the circuit 2 so as to finely adjust the board 1 in warpage. By this setup, the incomplete bonding of wires, the imperfect connection of an electronic component to pads by soldering, and the incomplete insertion of a printed wiring board into an equipment case caused by the warpage of a printed wiring board can be surely prevented.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to a thin board (with a board thickness of 0.1-1. .Omm) printed wiring board.

[Prior Art] In a printed wiring board, a conductor circuit made of a pattern of copper, which is a conductor, is formed on the surface of an electrically insulating substrate, and the conductor circuit is provided on one or both sides of the substrate. In order to meet the demands for lighter and thinner electronic devices, thin printed wiring boards with a board thickness of 0.1 to 1.0 mm have been used.

[Problems to be Solved by the Invention] Printed wiring boards are placed in high-temperature environments under various conditions as described below during their manufacturing process and when electronic components are mounted.

■Heat press between base material and copper foil during formation of copper-clad laminate...150-250°C (residual internal stress) ■Thermosetting after solder resist printing...120-706C ■Wire bond...・100~200°C ■Guibond (fixing IC chip to substrate)...120~200°
C ■ Solder reflow...200-260°C On the other hand, the coefficient of thermal expansion of copper is 1.4 X I O-5/'C, and the coefficient of thermal expansion of the base material varies depending on the type of base material, or the glass transition Point (14
1.2-1. 6 x 10
When the temperature exceeds the glass transition point at -510C, the coefficient of thermal expansion further increases. Therefore, when the printed wiring board is placed in a high temperature state, there is a difference in thermal expansion between the conductive circuit portion and the board portion. When the board thickness was large, the difference in thermal expansion had little effect. However, as printed wiring boards become thinner, warpage occurs in the printed wiring boards, especially when conductive circuits are formed on only one side of the printed wiring boards.

Then, when wire bonding is performed in a state where warpage has occurred as shown in FIG. When thermocompressing and cutting the wiring pattern, the end of the gold wire 23 is attached to the capillary 21.
This may cause the inconvenience of not being able to come off. This is because the gold wire 23 is cut by crushing the gold wire 23 with the tip of the capillary 21, or by cutting the gold wire 23 on the printed wiring board 20.
This is because if there is any warpage, the crushing will not be performed reliably.

Furthermore, when electronic components are mounted on a printed wiring board using the reflow method, if the cream solder is warped during supply, the thickness of the cream solder will vary. Then, a connection failure occurs in a portion where the amount of solder is small, and a portion where there is a large amount of solder may flow to an adjacent wiring pattern portion during beam flow, resulting in a short-circuit condition.

Furthermore, even if the cream solder is supplied normally without any warping, if the cream solder is warped during reflow, the solder may flow to a location other than the required location, resulting in the above-mentioned defect.

Furthermore, when a printed wiring board on which electronic components are mounted is assembled into a device such as a case, there is a problem that if the printed wiring board is warped, the assembly will be defective.

Furthermore, even in a printed wiring board in which conductor circuits are present on both the front and back sides, when the position or wiring direction of the conductor circuits 24 formed on the front surface A and the back surface B are different, as shown in FIGS. 5(a) and 5(b). In this case, warping occurs and the state of the warping becomes complicated. In order to prevent the occurrence of warpage, it has been considered to form a solid pattern 25 in a wide area where there is no conductor circuit 24 on the opposite side of the part where the conductor circuit 24 is formed, as shown in FIG. However, FIG. 5(a).

When a solid pattern 25 is formed in an empty area of a printed wiring board on which a conductive circuit 24 is formed as shown in FIG.
In addition to the effect of canceling out the warping element in the direction, it also has the effect of increasing the warping element in the arrow direction caused by the conductor circuit 24 on the B side, so warping cannot be prevented.

The present invention has been made in view of the above problems, and includes:
The purpose is to provide a printed wiring board that can prevent warping caused by thermal expansion even when the thickness of the board is reduced.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a thin printed wiring board in which a conductor circuit is formed on at least one side of the board for mounting and connecting electronic components. A dummy pattern was formed in an empty area on the substrate opposite to the conductor circuit where no conductor circuit was formed using a conductor made of line elements in the same direction as the wiring direction of the conductor circuit.

Further, in the invention as set forth in claim 2, the outer periphery of the dummy pattern is surrounded by an outer periphery line pattern.

Furthermore, in the invention as set forth in claim 3, the dummy pattern is connected to a conductor circuit for power supply or grounding formed on a printed wiring board.

[Function] In the present invention, the dummy pattern is located on the opposite side facing the position where the conductor circuit is formed, and is composed of line elements in the same direction as the wiring direction of the conductor circuit, so that even if the printed wiring board is placed in a high temperature state, , the conductor circuit and the dummy pattern expand in the same direction, and a force in the same direction acts on both sides of the printed wiring board. That is, unlike the case where the solid pattern is formed as a dummy pattern, the dummy pattern acts only to offset the warping element due to thermal expansion of the conductor circuit on the opposite side.

When the outer periphery of the dummy pattern is surrounded by an outer peripheral line pattern, it becomes easy to distinguish between the dummy pattern and the wiring pattern constituting the conductor circuit.

In addition, if a dummy pattern is connected to a conductor circuit for a power supply formed on a printed wiring board, it is possible to increase the current capacity of the power supply, and the heat generated from the power supply is directed to the dummy pattern, which spreads over a wide area. Heat is effectively dissipated from the dummy pattern on the surface area.

On the other hand, when the dummy pattern is connected to a grounding conductor circuit formed on a printed wiring board, the grounding conductor becomes a conductor with a wider area and the grounding becomes stable.

[Example 1] Hereinafter, a first example embodying the present invention will be described with reference to FIG.

As shown in FIG. 1(a), on the surface A of the printed wiring board 1, a large number of pads 3 constituting a conductor circuit 2 are formed in two rows extending vertically in the figure. A wiring pattern 4 connecting the pads 3 in both rows is formed so as to extend along the longitudinal direction (vertical direction) of the pad 3 and partially extend in the lateral direction.

On the other hand, as shown in FIG. 1(b), a conductive circuit 2 and a dummy pattern 5 are formed on the back surface B of the printed wiring board l. The wiring pattern 6 constituting the conductor circuit 2 is on the surface A.
A part of the wiring pattern 4 formed in the wiring pattern 4 is formed to extend in the horizontal direction at a position substantially corresponding to the horizontally extending portion. The wiring pattern 6 is connected to a part of the wiring pattern 4 formed on the surface A via a through hole 7. The dummy pattern 5 is formed at a position corresponding to a vertically extending portion of the wiring pattern 4 on the surface A, with the wiring pattern 6 sandwiched therebetween. The dummy pattern 5 consists of a large number of straight line patterns 5a having line elements in the same direction as the wiring direction of the wiring pattern 4, and the outer line pattern 8 surrounds the straight line patterns 5a.
The straight line pattern 5a and the outer peripheral line pattern 8 are connected to each other.

The printed wiring board 1 configured as described above is composed of a large number of linear patterns 5a having line elements in the same direction as the wiring direction of the conductor circuit 2 on the opposite side of the dummy pattern 5. 1 is heated, the warping element caused by the conductor circuit 2 is offset by the dummy pattern 5, and unlike a solid pattern, no new warping element is generated, so warping of the printed wiring board l is reliably prevented. . By increasing or decreasing the thickness and number of the straight line patterns 5a in accordance with the conductor circuit 2, fine adjustment of the warpage becomes possible. Further, it is possible to similarly deal with warpage caused by the difference in thickness of the resist layer between the front and back surfaces of the printed wiring board l.

Moreover, since the dummy pattern 5 is surrounded by the outer peripheral line pattern 8, it is easy to distinguish it from the wiring pattern 6, which facilitates work during product inspection.

Furthermore, when the dummy pattern 5 is connected to a power supply conductor circuit (not shown), it becomes possible to increase the current capacity of the power supply, and the heat generated from the power supply is led to the dummy pattern 5, resulting in a large surface area of the dummy pattern. Heat is effectively dissipated from 5. Straight line pattern 5 forming dummy pattern 5
If the width and spacing of a are reduced (and the number is increased,
Compared to the case where solid patterns are formed in the same area, the surface area of each linear pattern 5a increases by the area of the side surface, and the heat dissipation effect is improved.

On the other hand, when the dummy pattern 5 is connected to a grounding conductor circuit (not shown) formed on the printed wiring board 1,
It becomes a grounding conductor or a conductor with a wider area, which stabilizes the grounding.

[Example 2] Next, a second example will be described with reference to FIG. In this embodiment, the conductor circuit 2 is formed only on the surface A of the printed wiring board 1, as shown in FIG. 2(a). A dummy pattern 5 is formed on the back side B of the printed wiring board 1 at a position corresponding to the conductor circuit 2 on the front side A, as shown in FIG. 2(b).

The dummy pattern 5 is formed from a large number of linear patterns 5a arranged to correspond to the bent state of the wiring pattern 4, and a part of the outer peripheral line pattern 8 constitutes the dummy pattern 5. This embodiment also exhibits the same effects as those of the previous embodiment.

[Embodiment 3] Next, a third embodiment will be described with reference to FIG. In this embodiment, as in the second embodiment, the conductor circuit 2 is formed only on the surface A of the printed wiring board l. The conductor circuit 2 includes a large number of pads 3 arranged on the upper, lower, left and right sides of the electronic component mounting section 9.
and a wiring pattern 4 extending from the pad 3. A portion of the wiring pattern 4 is formed to extend along the periphery of the printed wiring board l. As shown in FIG. 3(b), on the back side B of the printed wiring board 1, there are a dummy pattern 5 extending along the periphery of the printed wiring board 1, an electronic component mounting portion 9 on the front surface, and a dummy pattern 5 disposed on the top, bottom, left and right sides of the top surface. A large number of pads 3 and dummy patterns 10 corresponding to part of the wiring pattern 4 extending from the pads 3 are formed. The dummy pattern 10 is formed in a lattice shape with vertical and horizontal linear patterns 10a having larger intervals than the wiring pattern 4 on the surface A, and is surrounded by an outer line pattern 8.

This embodiment also exhibits the same effects as both of the embodiments described above.

Note that the present invention is not limited to the above embodiments,
For example, surrounding the outer peripheral portions of the dummy patterns 5 and 10 with the outer peripheral line pattern 8 may be omitted.

Further, when the conductive circuit 2 formed on the side opposite to the side on which the dummy pattern 10 is formed has the wiring pattern 4 in both the vertical and horizontal directions as in the third embodiment, the conductive circuit 2 forms an angle of 45 degrees with respect to both the vertical and horizontal directions. The dummy pattern 10 may be formed by a large number of linear patterns that are orthogonal to each other.

[Effects of the Invention] As detailed above, according to the present invention, even when the thickness of the substrate of a printed wiring board becomes thin, warping caused by thermal expansion can be prevented, and wires caused by warping can be prevented. It is possible to reliably prevent defective work during bonding, poor connections and short circuits when soldering electronic components to pads, and defective installation of printed wiring boards into equipment such as cases.

Further, when the outer peripheral portion of the dummy pattern is surrounded by an outer peripheral line pattern, it becomes easy to distinguish between the dummy pattern and the wiring pattern constituting the conductor circuit.

In addition, if a dummy pattern is connected to a conductor circuit for a power supply formed on a printed wiring board, it is possible to increase the current capacity of the power supply, and the heat generated from the power supply is directed to the dummy pattern, which spreads over a wide area. Heat is effectively dissipated from the dummy pattern on the surface area.

Furthermore, when the dummy pattern is connected to a grounding conductor circuit formed on a printed wiring board, the grounding conductor becomes a conductor with a wider area, and the grounding becomes stable.

[Brief explanation of drawings]

FIG. 1(a) is a schematic partial plan view of the front side of a printed wiring board of the first embodiment embodying the present invention, FIG. 1(b) is a schematic partial plan view of the back side of the same, and FIG. a) is a schematic partial plan view of the front side of a printed wiring board according to a second embodiment of the present invention, FIG. 2(b) is a schematic partial plan view of the back side of the printed wiring board, and FIG. FIG. 3(b) is a schematic partial plan view of the front side of the printed wiring board of the third embodiment embodying the invention
) is a schematic partial plan view of the back side, FIG. 4 is a schematic side view showing the state of wire bonding work when the printed wiring board is warped, and FIG. 5(a) is a diagram of the conventional printed wiring board. A schematic partial plan view of the front side and FIG. 5(b) are the same (a schematic partial plan view of the back side, and FIG. 6 is a schematic partial plan view of the back side of another conventional printed wiring board. Printed wiring board 1, conductor circuit 2, wiring pattern 4.6,
Dummy patterns 5, 10, outer line pattern 8, surface A,
Back side B0

Claims (3)

[Claims] 1. In a thin printed wiring board in which a conductor circuit (2) is formed on at least one side of the board for mounting and connecting electronic components, the conductor circuit (2) on the opposite side to the conductor circuit (2) on the board 1. A printed wiring board characterized in that a dummy pattern (5) is formed by a conductor made of line elements in the same direction as the wiring direction of the conductor circuit (2) in an empty area where the conductor circuit (2) is not formed. 2. The printed wiring board according to claim 1, wherein the outer periphery of the dummy pattern (5) is surrounded by an outer peripheral line pattern (8). 3. The printed wiring board according to claim 1 or 2, wherein the dummy pattern (5) is connected to a conductor circuit for power supply or grounding formed on the printed wiring board.