Patent Application
20140313687
1. Technical Field
The present disclosure relates to printed circuit board assemblies, and more particularly to a printed circuit board assembly with a shielding structure.
2. Description of Related Art
Printed circuit boards (PCBs) are designed for coupling control chips to electronic devices. Signal transmission lines are laid on the PCB to transmit signals, such as high-speed differential signals. However, some of the signal transmission lines are required to be laid adjacent to side edges of the PCB. High-speed differential signals of the signal transmission lines generate EMI, which causes an edge effect in the signal transmission lines and causes digital system failure due to false signals appearing on a receiver.
Therefore, there is a need for improvement in the art.
Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean “at least one.”
The PCB 10 comprises a top surface 11, a bottom surface 12, a first side surface 13, a second side surface 14, a third side surface 15, and a fourth side surface 16. A signal transmission line 20 is laid in the top surface 11 adjacent to the third side surface 15. Four through holes 17 are defined in the PCB 10. Two of the four through holes 17 are adjacent to the first side surface 13, and the other two through holes 17 are adjacent to the second side surface 14.
A shielding structure 30 is attached to the PCB 10 and comprises a first shielding piece 31, a second shielding piece 32, a third shielding piece 33, and a fourth shielding piece 34 connected end-to-end. The first shielding piece 31, the second shielding piece 32, the third shielding piece 33, and the fourth shielding piece 34 securely contact the first side surface 13, the second side surface 14, the third side surface 15, and the fourth side surface 16, respectively. A flange 35 extends from an upper edge and a lower edge of each of the first shielding piece 31, the second shielding piece 32, the third shielding piece 33, and the fourth shielding piece 34. Two mounting holes 36 are defined in each top flange 35 and each bottom flange of the first shielding piece 31 and the second shielding piece 32. In one embodiment, the flanges 35 are ladder-shaped, and a height of each flange 35 and each bottom flange is about 10 mil to about 20 mil.
The top flanges 35 and the bottom flanges closely contact the top surface 11 and the bottom surface 12. Thus, the top flanges 35, the bottom flanges, the first shielding piece 31, the second shielding piece 32, the third shielding piece 33, and the fourth shielding piece 34 cooperatively surround edges of the PCB 10. Each mounting hole 36 is aligned with a corresponding through hole 17, and a fastener (not shown) is received through each through hole 17 and each mounting hole 36 to fix the shielding structure 30 to the PCB 10. A diameter of each through hole 17 is substantially equal to a diameter of each mounting hole 36. A length of the first shielding piece 31 and a length of the second shielding piece 32 are slightly greater than a width of the PCB 10. A length of the third shielding piece 33 and a length of the fourth shielding piece 34 are slightly greater than a length of the PCB 10. Widths of the first shielding piece 31, the second shielding piece 32, the third shielding piece 33, and the fourth shielding piece 34 are substantially equal to a thickness of the PCB 10. The shielding structure 30 can be made of copper or aluminum, but can be made of other suitable materials.
Using a software application called Computer Simulation Technology (CST) to simulate an EMI value of the PCB 10, the following test results of one embodiment were obtained and are shown below. For the simulated conditions, the length of the PCB 10 is 5000 mil, the width of the PCB 10 is 3000 mil, and the thickness of the PCB10 is 54.2 mil. A distance between the signal transmission line 20 and the third side surface 15 is 10 mil. A length of the signal transmission line 20 is 4990 mil. A width of the signal transmission line 20 is 5 mil. The simulation according to the simulated conditions shows that when a frequency of high-speed differential signals transmitted in the signal transmission line 20 increases from 0.2 GHZ to 10 GHZ, the corresponding EMI value for each frequency value is indicated in the table below:
The EMI values of the PCB 10 are represented by electrical field strength per meter (V/M). According to the table, the EMI values of the PCB 10 using the shielding structure 30 are significantly reduced. Thus, an edge effect of the signal transmission line 20 is also reduced.
Even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and the arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201310135310X | Apr 2013 | CN | national |
