Printed circuit board and methods for manufacturing a printed circuit board

Abstract

A printed circuit board, PCB (400), in the form of a rectangle, wherein the printed circuit board comprises: a fiber layer (110) formed from intertwined woven glass fibers; a metal layer (120, 130) attached to a surface of the fiber layer; and a pair of differential signal tracks (410) formed on the metal layer (120, 130), wherein extension directions of the optical fibers are arranged at acute angles with respect to a longitudinal direction of the rectangle, and the pair of differential signal traces (410) extends along a latitude direction or the longitudinal direction of the rectangle, wherein the acute angles are 40°-44° or 46°-50°.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates generally to communications technology and, more particularly, to a PCB (printed circuit board), a core for manufacturing the PCB, and a method for manufacturing the PCB. Description of the state of the art

[0002] For differential signals, two output drivers are typically used to drive a pair of independent and parallel differential signal paths to transmit the digital data. The phase of the signals transmitted in the pair of differential signal paths is opposite to each other, and the information is conveyed using the difference between the signals in the pair of differential signal paths. A differential signal is often used in a GPU (graphics processing unit) board. The high-speed settings in the GPU board, such as PEX, TMDS, and FBIO_CLK / DQS, typically use a differential signal to transmit and receive data. The quality of these signals is particularly important for the performance of the GPU board.

[0003] In a digital system chip, with the increase in transmission speed and frequency, as well as the miniaturization of VLSI (Very Large Scale Integrated Circuits), the relationship between SI (signal integrity) and the microstructure of the circuit board has become one of the most important issues for layout engineers to consider. The microstructure of the circuit board has begun to influence the quality of the differential signal. For example, different propagation delays occur between the pair of differential signal paths. For a circuit board with a lower transmission speed, the difference between the propagation delays is negligible. However, for the GPU board, the transmission speed of differential signals is typically greater than 2.5 GT / s, or even up to 10 GT / s (for example, for a GF10x GPU board with GDDR5 memory).Therefore, the difference in propagation delays can lead to greater rise time distortion between the pair of differential signal traces. This rise time distortion can exceed the mismatch tolerance range of the pair of differential signal traces and can therefore seriously affect the performance of the GPU board. US 2007 / 0 110 388 A1 describes a method for creating fiber-reinforced printed circuit boards. US 2005 / 0 034 893 A1 describes a printed circuit board with a fiber optic zigzag pattern.

[0004] Therefore, there is a need to provide a PCB board, a core for manufacturing the PCB board, and a method for manufacturing the PCB board to solve the above-mentioned problem in the prior art and to provide a printed circuit board in which influence of the substrate of the signal path is reduced and which is easy to manufacture. OVERVIEW OF THE INVENTION

[0005] This object is achieved by the features of the independent claims. To solve the above-mentioned problem, a PCB board according to claim 1 is provided. The PCB board is, among other things, in the shape of a rectangle and comprises a fiber layer and a metal layer attached to a surface of the fiber layer. The fiber layer is made of intertwined woven or knotted glass fibers, the extension directions of the glass fibers forming acute angles with a longitudinal direction of the rectangle. A pair of differential signal paths is formed on the metal layer, and the pair of differential signal paths extends along a width direction or along the longitudinal direction of the rectangle.

[0006] Preferably, the metal layer is fixed to the fiber layer by epoxy resin.

[0007] Preferably, the fiber layer is made of a glass fiber layer and epoxy resin.

[0008] Preferably, the metal layer is a copper foil.

[0009] There is further provided a method for manufacturing the PCB board according to claim 5. The method includes, among other things: providing a fiber layer made of intertwined woven glass fibers; attaching a metal layer to a surface of the fiber layer to form a core void; cutting the core void into a rectangle and allowing a longitudinal direction of the rectangle to form acute angles with extending directions of the glass fibers; and forming a pair of differential signal traces on the metal layer, the pair of differential signal traces extending along a width direction or along the longitudinal direction of the rectangle.

[0010] In summary, the PCB provided by the present invention can effectively reduce the possibility of rise distortion during the differential signal transmission process by adjusting the angle between the optical fibers and the core edge. Layout design engineers do not need to adjust or redesign the original circuit layout accordingly. Consequently, the original manufacturing process and manufacturing costs can be maintained if the problems existing in the prior art can be solved.

[0011] A number of simplified concepts are included in the overview of the invention, which are further described in the detailed description below. The overview of the invention neither implies that it is intended to limit the essential features and necessary technical features of the technical solution to be protected, nor does it imply that it is intended to define the scope of protection of the technical solution to be protected.

[0012] Advantages and features of the present invention are described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following drawings of the present invention are used as part of the present invention to enhance the understanding of the present invention, the embodiments and descriptions of which are shown in the drawings to explain the principle of the present invention. In the drawings, Fig. 1 is a schematic sectional view of a core according to an embodiment of the invention; Fig. 2 is a microscopic enlarged view of a fiber layer according to an embodiment of the invention; Fig. 3 is a schematic plan view of the fiber layer according to an embodiment of the invention; Fig. 4 is a schematic view of a PCB board according to an embodiment of the invention; Fig. 5 is a schematic plan view of the PCB board according to a comparative example, wherein a pair of differential signal paths is formed parallel or perpendicular to the optical fibers; and Fig. 6 is a flowchart for manufacturing the PCB board according to an embodiment of the invention. DETAILED DESCRIPTION

[0014] Numerous specific details are set forth in order to provide a more thorough understanding of the present invention in the following description. However, the present invention may be practiced without one or more of these details, as would be apparent to one skilled in the art. In other instances, some of the technical features known in the art have not been described to avoid obscuring the present invention.

[0015] Note that an element or layer may be directly "on," "adjacent to," "in association with," or "connected to" another element or layer, or an intermediate element or layer disposed therebetween, when it is stated that the element or layer is "on," "adjacent to," "in association with," or "connected to" another element or layer. On the other hand, if an element or layer is "directly on," "directly adjacent to," "directly in association with," or "directly connected to" another element or layer, there is no intermediate element or layer.

[0016] According to one aspect of the invention, a core 100 for manufacturing a PCB board is provided. The core 100 is in the shape of a rectangle. Fig. 1 is a sectional view of the core 100. The core 100 includes a fiber layer 110 and metal layers 120 and 130, as shown in Fig. 1 is shown.

[0017] The fiber layer 110 may be made of interwoven glass fibers. Fig. Figure 2 shows the structure of the intertwined woven glass fibers. Warp threads 210 and filler threads 220, formed from glass fibers, extend along the two perpendicular directions and are intertwined, forming a structure similar to a textile fabric, as shown in Fig. 2. For example, the fiber layer 110 can be manufactured by processing FR4 glass fibers, i.e., the warp threads 210 and the filler threads 220 are made of FR glass fibers. FR4 indicates a grade for a fire-resistant material that is self-extinguishing after ignition. To avoid rise distortion of the differential signal transmitted by the pair of differential signal paths, the extension directions of the glass fibers in the fiber layer 110 form acute angles with the longitudinal direction of the rectangle. Fig. 3 is a plan view of the fiber layer 110. As in Fig. 3, the extending directions of the warp threads 210 and the filler threads 220 form angles with the edges of the rectangular fiber layer 110, so that each warp thread 210 and each filler thread 220 forms an acute angle with the longitudinal direction of the fiber layer 110. Note that each warp thread 210 and each filler thread 220 also forms an acute angle with the width direction of the fiber layer 110. The effect achieved by this structure will be described in detail below.

[0018] It is back on Fig. 1; the metal layers 120 and 130 are attached to a surface of the fiber layer 110. Although Fig. 1 shows that the metal layers 120 and 130 are attached to an upper surface and a lower surface of the fiber layer 110, respectively. The metal layers 120 and 130 may be attached to only a single surface of the fiber layer 110 as needed. The circuit pattern is formed by etching the metal layers 120 and 130 when the core is used to manufacture the PCB, and thus, the metal layers 120 and 130 are preferably made of a metal material with high conductivity, such as silver, aluminum, tungsten, copper, or an alloy thereof. In view of stability and the etching process, etc., the metal layers 120 and 130 may preferably be copper foils.

[0019] For example, the metal layers 120 and 130 are attached to the fiber layer 110 using epoxy resin. The epoxy resin can melt and flow at high temperatures, allowing the metal layers 120 and 130 to be attached to the fiber layer 110. In addition, epoxy resin also exhibits excellent heat resistance, stability, and insulation performance in low-temperature environments (within the temperature range in which the PCB board is typically used).

[0020] Preferably, the fiber layer 110 is made of a glass fiber layer and epoxy resin. The epoxy resin can cover the surface of the glass fiber layer. When the metal layers 120 and 120 are attached to the fiber layer 110 by a hot-pressing process, the epoxy resin can optionally serve only as an adhesive between the fiber layer 110 and the metal layers 120 and 130, but it can also fill the gap in the glass fiber layer. The glass fiber layer can contain one or more of the glass fiber fabric, the pre-impregnated glass fiber fabric, and the pre-impregnated glass fiber nonwoven fabric, etc.

[0021] According to a further aspect of the invention, a PCB board 400 is also provided. A pair of differential signal paths 410 are formed on the PCB board 400, as shown in Fig. 4. In particular, the pair of differential signal paths 410 can be formed by etching the metal layers 120 and / or 130 of a core 100 mentioned above. To avoid the slope distortion of the differential signal transmitted via the pair of differential signal paths 410, the pair of differential signal paths 410 extends along a width direction or a length direction of the rectangle such that the pair of differential signal paths 410, as well as the warp threads 210 and the fill threads 220, are arranged at an angle relative to the width direction or the length direction. In view of the unexpected technical effect, the applicant analyzes the possible reason for this as follows:

[0022] When the pair of differential signal traces 510 is formed along the filler threads 220, the first differential signal trace 510A of the pair of differential signal traces 510 may land directly on the filler thread 220, while the second differential signal trace 510B of the pair of differential signal traces 510 may be disposed between two filler threads 220. The adhesive (such as epoxy resin, etc.) may enter between the warp threads 210 and the filler threads 220. It causes the ambient substance around the first differential signal trace 510A to be different from the ambient substance around the second differential signal trace 510B. That is, the dielectric constant of the dielectric layer around the first differential signal trace 510A is different from that of the dielectric layer disposed around the second differential signal trace 510B.The dielectric constant of a dielectric layer composed of several materials can be calculated using the following formula:. Dk=Dk(a)×M(a)%+Dk(b)×M(b)% where D k is the total dielectric constant of a dielectric layer, D k (a) is the dielectric constant of the first material contained in the dielectric layer, M(a)% is the mass fraction of the first material in the dielectric layer, D k (b) is the dielectric constant of the second material contained in the dielectric layer, and M(b)% is the mass fraction of the second material in the dielectric layer.

[0023] The warp threads 210 and the filler threads 220 are made of glass fibers, and the dielectric constant of the glass fibers is approximately 5.6. However, the dielectric constant of the epoxy resin used in FR4 glass fibers is approximately 3.2. Thus, it can be seen that the dielectric constants of the dielectric layer around the first differential signal path 510A and the second differential signal path 510B are different, and the dielectric constant of the dielectric layer around the second differential signal path 510B is also relevant to the dimensions of the glass fibers and the gap between the glass fibers. The difference between the dielectric constants of dielectric layers adjacent to the first differential signal path 510A and the second differential signal path 510B can lead to an impedance mismatch and, therefore, can cause transmission delay.For a low-speed PCB, slew distortion is negligible. However, for a higher-speed PCB, slew distortion may exceed the mismatch tolerance range of the pair of differential signal traces.

[0024] When the pair of differential signal paths 510 is formed along the warp threads 210, a phenomenon similar to the one mentioned above may occur. That is, one of the two differential signal paths lands on one warp thread 210, while the other is located between two warp threads 210. The ambient substances around the pair of differential signal paths are similar to those described previously, and thus, this will not be described in detail herein.

[0025] The PCB 400 provided by the invention allows the two differential signal paths 410 to form an angle with the warp threads 210 and the fill threads 220, thus avoiding the aforementioned effect to some extent. A balance is made between the two differential signal paths 410 to reduce the impedance mismatch.

[0026] There is a possibility that the angle between the glass fibers and the edge of the rectangular core deviates from a predetermined value during core manufacturing, and this deviation is usually less than 5°. Therefore, the acute angle between the glass fibers and the edge of the rectangular core (i.e., the longitudinal direction) is 10°-80° to avoid the deviation caused by core manufacturing. In order to maintain the impedance of the first differential signal path 510A as closely as possible to the impedance of the second differential signal path 510B, according to the invention, the acute angles between the glass fibers and the edge of the rectangular core (the longitudinal direction) are 40°-50°.

[0027] It should be noted that the PCB board may include one or more cores depending on the structure and function of the PCB board to be manufactured. If the PCB board includes multiple cores, the pair of differential signal traces 410 may be fabricated on one or more of the multiple cores.

[0028] In summary, the PCB provided by the present invention can effectively reduce the possibility of rise distortion during differential signal transmission by adjusting the angle between the optical fibers and the core edge, and layout engineers do not need to readjust or redesign the original circuit layout. Consequently, the original manufacturing process and manufacturing costs can be maintained even if the problems existing in the prior art are still solved.

[0029] According to yet another aspect of the invention, a method for manufacturing the PCB board is provided. The method comprises the following steps:

[0030] First, in step 601, a fiber layer made of interwoven glass fibers is provided. The warp threads 210 and the filler threads 220 made of glass fibers extend along two perpendicular directions and are interwoven to form a structure similar to the textile fabric shown in Fig. 2 is shown.

[0031] Subsequently, in step 602, a metal layer is attached to a surface of the fiber layer to form a core void region. The metal layers may be attached to an upper surface and a lower surface of the fiber layer, respectively, or they may be attached only to the upper surface or the lower surface. Preferably, the metal layer is attached to the fiber layer using epoxy resin. Preferably, the fiber layer is made of the glass fiber layer and the epoxy resin. The epoxy resin may cover the surface of the glass fiber layer. When the metal layer is attached to the glass fiber layer by a hot-pressing method, the epoxy resin not only serves as an adhesive between the fiber layer and the metal layer but also fills the gap in the glass fiber layer. For example, the metal layer may be a copper foil.

[0032] Next, in step 603, the core void is cut into a rectangle, and the longitudinal direction of the rectangle forms acute angles with the extension directions of the optical fibers. Considering the variations introduced by the manufacturing process, the acute angles may preferably be 10°-80°. To best match the impedance of the first differential signal path 510A to the impedance of the second differential signal path 510B, the acute angles may further preferably be 40°-50°.

[0033] Finally, in step 604, a pair of differential signal paths is formed on the metal layer. The pair of differential signal paths extends along the width direction or the length direction of the rectangle, so that a balanced relationship is formed between the pair of differential signal paths. For example, the pair of differential signal paths is formed on the metal layer through an etching process. The etching process not only has higher accuracy but can also create the circuit pattern with smaller dimensions (down to several tens of nanometers). Therefore, the uniformity of the shape and dimensions of the pair of differential signal paths is improved, so that the rise distortion of the signal output from the pair of differential signal paths is reduced.

[0034] In the PCB manufacturing process, only the angles between the core's glass fibers and the core's edge are adjusted during the core cutting process. This reduces the likelihood of rise distortion during the differential signal transmission process and avoids impacting the GPU board's performance. Furthermore, the process has no impact on the work of layout designers. Re-adjusting or redesigning the circuit layout is usually a tedious and time-consuming task.

Claims

[1] A printed circuit board, PCB (400), in the shape of a rectangle, the printed circuit board comprising: a fiber layer (110) formed from interlaced woven glass fibers; a metal layer (120, 130) attached to a surface of the fiber layer; and a pair of differential signal paths (410) formed on the metal layer (120, 130), wherein extension directions of the glass fibers are arranged at acute angles with respect to a longitudinal direction of the rectangle, and the pair of differential signal paths (410) extend along a width direction or the longitudinal direction of the rectangle, the acute angles being 40°-44° or 46°-50°. [2] The printed circuit board according to claim 1, wherein the metal layer is fixed to the fiber layer by epoxy resin. [3] The printed circuit board according to claim 1, wherein the fiber layer is made of a glass fiber layer and epoxy resin. [4] The printed circuit board according to claim 1, wherein the metal layer is a copper foil. [5] A method of manufacturing a printed circuit board, PCB (400), comprising: Providing (601) a fiber layer (110) made of intertwined woven glass fibers; Attaching (602) a metal layer (120, 130) to a surface of the fiber layer to form a core void area; Cutting (603) the core void into a rectangle such that a longitudinal direction of the rectangle is arranged at acute angles with respect to extension directions of the glass fibers, the acute angles being 40°-44° or 46°-50°; and Forming (604) a pair of differential signal traces (410) on the metal layer, wherein the pair of differential signal traces extends along a width direction or the length direction of the rectangle.

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