MXPA06009581A - Flexible circuit board assembly - Google Patents

Abstract

A flexible circuit board assembly includes a rigid circuit board (104) having a first portion (204) and a second portion (208) separated by a bending region (206). A plurality of grooves (30, 40, 50) are cut into the bending region (206). The grooves (30, 40, 50) are cut substantially parallel to an axis about which the bending region (206) is bent. Preferably, the grooves (30, 40, 50) are located on an inside bending radius of the circuit board (104), but can be located on the outside radius, or both.

Description

C CPQ DE? INVENTION The present invention relates generally to printed circuit boards, and in particular, to the use of rigid circuit boards in a flexible assembly.

? TECEDENTS OF? INVENTION Control systems for automotive engines are placed in a confined space • in an environment subject to high ambient temperatures and extreme vibrations. Typically to increase the thermal performance and protection against vibration of the motor, a printed circuit board that includes control circuits that are fixed to a stiffener that can be bent to produce a reduced size module and to dissipate heat as well. For example, in an application using a printed circuit board having a bent flexible circuit, such as is used to pack an electronic control unit, the printed circuit board is mounted to an aluminum stiffener. The stiffener provides the mechanical support for the printed circuit board and assists in the heat dissipation generated by the components in the printed circuit board to conductively transfer the heat of the components to the underlying stiffener. Referring now to FIGS. 1 and 2, an electronic control unit (ECU) 100 of the prior art is illustrated. Figure 1 is an isometric perspective of an end view of the electronic control unit 100. Figure 2 is a cross-sectional side view of the electronic control unit 100. The electronic control unit 100 includes a flexible printed circuit board 104. which is fixed to a stiffener 106 by means of the use of an adhesive 202. Typically, the circuit board 104 has a number of electronic components 102 mounted on the surface thereof. The adhesive 202 is placed between the stiffener 106 and the printed circuit board 104 and the functions for securing the printed circuit board to the stiffener. After having secured the flat stiffener, the stiffener and the printed circuit board assembly are bent, resulting in a bent printed circuit board consisting of two main portions 204, 208 at an angle to each other and connected by a section. bent 206 captured within a space 112 of bent region 116 of stiffener 106. To provide a bend in the circuit board, a flexible circuit board is used. Unfortunately, flexible circuit boards cost more than their rigid counterparts. For example, a circuit board (FR4) with flexible glass fiber epoxy resin costs more than a rigid FR4 circuit board. Basically, the difference in price is due to the problems that manufacturers have in the handling of flexible boards through the operations of the welding mask and panel plating, resulting in lower yields and higher costs as a result. Additionally, flexible circuit boards have become more complex. As the functionality of the electronic control units has increased over time, the corresponding circuits have become denser and more complex. As a result, the control units no longer use two-layer printed circuit boards, such as the printed circuit board 104, but use four-layer printed circuit boards, as a result of the manufacturing process of the printed circuit boards. Four layer is a thicker flexible circuit, even when the bending section remains as a two layer circuit. Due to its thickness, it is now recognized that the flexible circuit boards break and split at the time of bending, unless a long bending radius is achieved, resulting in a control module to be discarded. Discarded control modules result in waste and excessive manufacturing costs, especially when printed circuit boards must be placed several components before bending. One solution has been to provide few layers on the circuit board in the bending section than in the flat sections. Another solution has been to heat the circuit board during bending. Both solutions require additional steps in the unusual procedure in either the manufacture of the circuit board or the assembly of the electronic control unit. Thus, there is a need for a method and apparatus for providing the benefits of rigid circuit boards in a flexible printed circuit board assembly.

BRIEF DESCRIPTION OF THE FIGURES The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with the additional objects and advantages thereof, can be better understood by referring to the following description, considered together with the appended figures, in several figures in which the numerical references identify the identical elements, wherein: 1 is an isometric perspective of an end view of an electronic control unit of the prior art. Fig. 2 is a cross-sectional side view of the electronic control unit of Fig. 1. Fig. 3 is a cross-sectional side view of the flexible circuit board according to a first embodiment of the present invention. Figure 4 is a cross-sectional side view of the flexible circuit board according to a second embodiment of the present invention. Figure 5 is a cross-sectional side view of the flexible circuit board according to a third embodiment of the present invention. Figure 6 is a top view of the stiffener of Figure 3, before bending, with an adhesive applied to the stiffener according to an embodiment of the present invention. Figure 7 is a top view of the electronic control unit of Figure 3, before bending and after mounting a circuit board in the stiffener and after having placed the solder paste in the circuit board in accordance with a embodiment of the present invention. Fig. 8 is a cross-sectional side view of the electronic control unit with the flexible circuit board assembly of Fig. 3. Fig. 9 is a logic flow diagram of an assembly method of a flexible circuit board assembly for an electronic control unit including a stiffener and a circuit board according to an embodiment of the present invention.

DETAILED DESCRIPTION D? THE INVENTION The present invention provides a method and apparatus for a rigid circuit board for use in a flexible printed circuit board assembly. The electronic control unit (ECÜ) includes a rigid circuit board having a first portion interconnected to a second portion through a bent region configured to be flexible. The electronic control unit further includes a substantially rigid substrate (eg, aluminum) or stiffener having a first portion interconnected to a second portion through a bending region with a space. The respective first and second portion of the stiffener and circuit board are joined together as a flat assembly. Subsequently, when the ECU is doubled, the bending region of the circuit board assumes a fold. The use of a specially configured rigid board results in cost savings based on the use of the flexible circuit board of the prior art. In various embodiments of the present invention, the bend in the bend region of the circuit board is facilitated by an opening or space in the bend region of the stiffener. Generally, one embodiment of the present invention encompasses an electronic control unit assembly system that includes a rigid or substantially stiffening substrate having a first portion and a second portion separated by a bend region. The rigid substrate has an interior surface and an exterior surface. The electronic control unit further includes a rigid circuit board having a first portion and a second portion separated by a bending region configured with parallel notches running towards the bend axis of the bending region. The region of bending of the substrate includes a space that extends outwardly from the inner surface of the substrate with the space of a certain size to accept the bending region of the circuit board. The first and second portions of the circuit board are fixed to the first and second respective portions of the substrate in a substantially flat configuration, through the use of an adhesive. The electronic control unit is bent at an angle between zero and one hundred and eighty degrees, such that the inner surface of the stiffener defines an interior region of the electronic control unit that contains the circuit board. When bent, the bending region of the circuit board achieves a shape with a long radius bend as a result of bending that extends towards the inner region of the stiffener in the space formed in the bending region of the substrate. Another embodiment of the present invention includes a method for forming a circuit board in an electronic control unit assembly that includes providing a rigid circuit board having a first part and a second part separated by a bending region and a substrate substantially rigid or stiffener having a first part and a second part separated by a bending region. The method includes a step to form a series of shaves in the bend region of the circuit board to make it more flexible therein. An additional step includes forming a space in the bending region of the substrate extending outwardly from an inner surface thereof with the size space to accept the bending region of the circuit board. The method includes an additional step for fixing the first and second portions of the circuit board to the respective first and second portions of the substrate. This may include the sub-steps for applying an adhesive to the inner surface of the flat stiffener and mounting the flat flexible circuit board on the surface of the stiffener through the adhesive. The method further includes the step for folding the rigid substrate in the bending region between the first and second portions such that the bending region of the circuit board deforms in the space of the substrate. Referring now to Figures 3-5, various embodiments of the circuit board for assembling in the electronic control unit 100 are illustrated. In these embodiments, a four-layer circuit board is shown. However, the present invention is applicable to any number of layers. Figure 3 is a side cross-sectional view of the circuit board 104, according to a first embodiment of the present invention, using a series of grooved notches 30 machined or marked in the bend region 206 of the rigid circuit board. Figure 4 is a cross-sectional side view of the circuit board 104, according to a second embodiment of the present invention, using a series of grooved notches 40 machined or marked in the bend region 206 of the rigid circuit board. Figure 5 is a cross-sectional side view of the circuit board 104, according to a third embodiment of the present invention, using a series of rectangular grooved notches substantially 50 machines or marked in the bend region 206 of the rigid circuit board. Although; show the slots that extend from the middle down (two layers) through a four-layer circuit board, several depths can be used. In addition, various transverse shapes may also be used which may be equally useful. The modalities shown represent the most common forms due to the ease of manufacture. With reference to Figure 8, the control unit 100 includes at least one electronic component 102, a circuit board 104, and a substantially rigid (stiffening) substrate 106. The electronic component 102 represents any of the electronic components or devices that they can be mounted to a printed circuit board such as, for example, a battery, a capacitor, a resistor, a semiconductor integrated circuit, a diode, an inductor, and a coil. The electronic component 102a is mounted to a surface of the circuit board 104. This can be achieved by welding the parts to the flat circuit board before or during the assembly of the control board in the stiffener 106. Typically, the circuit board 104 has a number of electronic components 102 mounted on the surface of the circuit substrate. These electronic components are electrically connected to each other through a number of conductive plates or templates (not shown) placed on the surface and in or through the inner layers of the circuit board 104. The circuit board 104 is a circuit board printed matter made of any number of materials known to those skilled in the art, such as epoxy glass, FR4, copper covered with resin, and polyimide. Preferably, four or more layers of FR4 material and up to five layers of circuits are provided. Of course, in the bending region, the circuits can not extend over the notches, so the circuits are limited to those layers of the circuit board that are not damaged during the grooving process. The circuit board 104 is secured to an interior surface of the stiffener 106. The circuit board 104 is secured to the interior surface by means of an adhesive 202, which is preferably a pressure sensitive adhesive film or tape (PSA). In another embodiment of the present invention, the adhesive 202 may be a heat-resistant liquid adhesive that is screen printed on the stiffener 106. Those skilled in the art understand that there are several techniques for securing a circuit board 104 to a surface , such as mechanical fasteners, such as screws or other adhesive laminates that may be placed on the surface, which may be used in the present invention without departing from the scope of the present invention. After assembly, stiffener 106 surrounds circuit board 104 and redesigns to protect circuit board 104 and electronic components 102 from electrical charges that can damage the circuit board and electrical components. The stiffener 106 also provides the mechanical support and dissipates the heat conductively to the circuit board 104. Preferably, the stiffener 106 is fabricated from materials that are rigid enough to provide a rigid mechanical support for the circuit board 104, i.e. It works as a stiffener or stabilizer, and has elements designed to protect electronic components from heat, water, chemicals and electrostatic charge, such as, aluminum, copper, steel, engineering grade plastic, magnesium, and zinc or any other material that is resistant to chemicals and elements commonly found in a car.

Preferably, the stiffener 106 of thermally conductive materials that transfer heat from the components 102 during the operation of the electronic control unit 100 is further manufactured, thereby helping the components to dissipate the heat. However, those skilled in the art understand that the electronic control unit 100 may be used in low power operations where there are thermal problems, and that the thermal conductivity of the stiffener 106 may be less important. The circuit board 104 and the stiffener 106 are folded into an approximate form in XU "However, any angle that is greater than zero and less than one hundred and eighty degrees in the present invention can be used. stiffener using any technique known to those skilled in the art The stiffener can be bent into two joints along a major axis through the stiffener between the first and second portions of the stiffener and the bending region. at ninety degrees at both junctions to form a "U" shaped assembly, such that the bending region is substantially perpendicular to the first and second portions of the substrate, which are substantially parallel to each other.

Figure 6 is a top view of the stiffener 106 before bending and with the adhesive 202 applied to the inside surface of the riper 106. As shown, the second portion 108 of the stiffener 106 af 101 is interconnected by the bridges 116 included in FIG. the region of bent. Figure 6 further illustrates the spaces 112 of the bending region. The bridges 116 and spaces 112 facilitate the "U" bending of the circuit board 104 at the time of bending the substrate and the stiffener. Figure 7 is a top view of the electronic control unit 100 after the circuit board 104 is mounted flat in the adhesive 102, and therefore, in the stiffener 106, and after the solder paste has been placed in the substrate and components 102 that have been assembled. Preferably, the components 102 are components that are mounted on a surface that can be self-placed on the circuit board 104 using techniques known in the art. Those skilled in the art will understand that it is not necessary to mount the components 102 on the surface. For example, the components 102 can be parts that can be manually placed through holes in the circuit board 104. However, using a liquid adhesive 202 that can be applied to the stiffener 106 and further utilize the components 102 that are mounted in the surface, an assembly procedure of the electronic control unit 100 can be fully automated. As shown in Figure 7, the recontrol board 104 includes a second portion 208 that is fixed to the second portion 108 of the stiffener 106, a bending region. 206 of the flexible circuit 104 which is located (but does not join) adjacent to the bend region 112 of the stiffener 106, and a first portion 204 that suffers the first portion 101 of the stiffener 106. The bend region is shown. divided into three sections, each of which covers one of the multiple spaces 112 of the stiffener 106, and further includes multiple cut-out sections 120 which they cover each of the multiple bridges 116 of the stiffener 106. However, it should be recognized that a few or more bending, opening and cutting regions can be provided. Notches provided (shown as reference 30 in Figure 3) in the bend region 206 of the circuit board 104, parallel to a bend axis 103 of the assembly. It should be recognized that the notches 40 of Figure 4, notches 50 of Figure 5, or other types of notches can be used. Referring now to Figure 8, there is illustrated an electronic control unit 100 for housing the flexible circuit board assembly according to a preferred embodiment of the present invention. Figure 8 is a cross-sectional side view of the electronic control unit 800. When the circuit board 104 and the stiffener 106 are folded, at least a portion of each of the three sections of the bend region 206 of the circuit board 104 extending into the spaces 112, and thereby, extend toward the interior region of the stiffener 106. Allowing it to be Extending the circuit board 104 to the inner region when the circuit board 104 and stiffener 106 are bent, the spaces 112 facilitate a "U" -shaped fold of the circuit board 104. The "U-shaped" fold gives as resulting in a long bend radius in the bend region 206 of the circuit board 104, thereby, any breakage or cracking that could occur when the circuit board 104 is folded is reduced. In practice, the rigid FR4 board will have a series of notches directed or applied in parallel from the surface to the folding axis on the side that will be compressed in the bend Although, the present invention could be used very well in the same way with the grooves located in a outside of the fold, this would result in stress stress in the grooves that could eventually result in stress of rupture. Therefore, it is preferred that the grooves located in an inner radius of the bend result in compressive forces in the grooves that do not have the potential to cause break stress. However, the slots may be located in an outer radius or in both outer and inner radii. In either case, the slots will make the board flexible enough to bend through a radius of seven millimeters. This can be achieved with five "V" shaped slots with an opening at the top of approximately 0.33 millimeters. The initial circuit board has a thickness of approximately 0.5 to 1.0 millimeter. The depth of the grooves is such that the remaining thickness of the board at the bottom of the grooves is approximately 0.25 to 0.38 millimeters. Other methods can be used to make the rigid FR4 flexible, such as pressing through the board in the flexible area to reduce the thickness in the selected areas, heating before bending to make the board more flexible, chemically etch the selected thin areas, chemically dissolve the FR4 material to soften the flexible area, or drill the board with small holes. Although the entire region in the bending region could be thinned, the resulting grooves and grooves formed therebetween provide lateral stiffness that is not available with a fully thinned region. It should also be recognized that a connector (not shown) could be mounted anywhere on the outer surface of the stiffener to electrically connect the circuit board through an appropriate hole in the stiffener. Figure 9 is a logical flow diagram 1000 of an assembly method of an electronic control assembly that includes a stiffener and a circuit board assembly according to any of the embodiments of the present invention. The logic flow diagram 1000 starts by providing reference 1002 with a rigid substrate substantially having a first portion and a second portion separated by a bending region and a rigid circuit board having a first part and a second part separated by a region of bent. Preferably, provisioning step 1002 includes providing a multilayer circuit board comprised of multiple layers of FR4 material formed with conductive signals, conductive pathways, and conductive plates to secure and interconnect the electrical components thereto, and further comprises the step for solder the reflow components of the circuit board. The logic flow continues to cut 1003 a plurality of grooves in the bending region that are substantially parallel to an axis near which the bending region is to be bent. The cut can be achieved according to the above description for Figures 3-5. The logic flow continues to set 1004 the first and second portions of the circuit board to the first and second respective portions of the substrate. This may include applying an adhesive to the stiffener and mounting the flat circuit board on the adhesive, and thus, on an inner surface of the stiffener. Subsequently, the circuit board and the stiffener 1006 are folded near the bend region at the junctions of the first and second parts and the bend region of the stiffener. Preferably, the first and second portions of the stiffener and the circuit are bent such that the first and second portions of the circuit board and the substrate are bent at approximately one hundred and eighty degrees angle to each other as measured from the surface inside. More preferably, the stiffener and circuit is bent in such a way that the grooves are compressed along the inner radius of the bending region. In response to the bending of the circuit board and the stiffener, the bending region of the bent flexible circuit board achieves a "UA" shape. In one embodiment of the present invention, an additional step includes forming 1008 at least one space in the region. of bending the stiffener extending outwardly from the inner surface of the stiffener to an outer surface thereof, and further includes a plurality of bridges interconnecting the first and second portions of the stiffener through the bending region. space is sized to accept the bending region of the circuit board, such that in bending step 1006, the bending region of the circuit board deforms in the space of the substrate to extend into an inner region of the stiffener through the space, thereby, a "U" -shaped fold is provided in the region of the flex circuit board. Preferably, the space has a depth of at least five millimeters extending outwardly from the inner surface of the stiffener. The present invention allows the replacement of flexible printed circuit boards with rigid circuits that will bend sufficiently in the selected areas to allow bending in a module. This eliminates the need to weld flexible bridges to couple to two rigid circuit boards, or to process very thin boards that need to be supported to pass through the assembly procedure. Since the present invention has been shown and described particularly with reference to the particular embodiments thereof, those skilled in the art will understand that various changes may be made. and the equivalents are replaced by elements thereof without departing from the broad scope of the invention. Additionally, various modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended to limit the invention to the particular embodiments described in the present invention, but the invention will include all modalities with respect to the scope of the appended claims.

Claims (8)

NEW DI! THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following is claimed as a priority: CLAIMS

1. - A circuit board assembly comprises: a rigid circuit board having a first and a second portion separately by means of a bending region, the rigid circuit board having a plurality of layers; and a plurality of grooves cut in the bending region, the grooves being cut in parallel substantially to an axis near which the bending region is bent, wherein the grooves are cut at least halfway through the board. rigid circuit.

2. The assembly according to claim 1, characterized in that the grooves are cut approximately two-thirds through the rigid circuit board.

3. The assembly according to claim 1, characterized in that the rigid circuit board comprises an epoxy fiberglass material.

4. - The assembly according to claim 1, characterized in that the slots are placed in an inner radius of the bending region.

5. The assembly according to claim 1, characterized in that the grooves have a profile in the form of "V".

6. The assembly according to claim 1, characterized in that the grooves have a substantially rectangular profile.

7. - The assembly according to claim 1, characterized in that the rigid circuit board is folded in the bending region at an angle of up to one hundred and eighty degrees, as measured from an inner surface of the rigid circuit board.

8. - The assembly according to claim 1, characterized in that the rigid circuit board includes electrical signals placed from the first portion to the second portion of the rigid circuit board through the folding region separating the first and second portion. in one of the uncut layers in the bend region of the rigid circuit board.