BGA is a common component on PCB
, such as CPU, North Bridge, South Bridge, AGP chip, card bus chip, etc In short, 80% of high-frequency signals and special signals will be pulled out of this type of package. Therefore, how to deal with the routing of BGA package has a great influence on important signals.
Generally, small parts around BGA can be divided into several categories according to their importance
1. by pass。
2. RC circuit of clock terminal. (in the form of series resistor and bank group; for example, memory bus signal)
3. EMI RC circuit (in the form of dampin, C, pull height; for example, USB signal).
4. Other special circuits (special circuits added according to different chips; for example, the temperature sensing circuit of CPU).
5. Small power supply circuit group below 40mil (in the form of C, l, R; this kind of circuit often appears in the AGP chip or chip with AGP function, and different power groups are separated by R and L).
6. pull low R、C。
7. General small circuit group (in the form of R, C, Q, u; no wiring requirements).
8.pull height R、RP。
The circuits of items 1-5 are usually the focus of placement. They will be arranged as close as possible to BGA and need special treatment. The sixth circuit is less important, but it will also be arranged closer to BGA. 7. The 8 items are general circuits, which belong to the signals that can be connected. Relative to the importance priority of small parts near BGA, the requirements on routing are as follows:
1. By pass = > when the same side of chip is the same as chip, the chip pin is directly connected to by pass, and then pulled out by pass to connect via to plane; when it is different from chip, it can share the same via with VCC and GND pin of BGA, and the line length should not exceed 100mil.
2. RC circuit of clock terminal = > there are requirements for line width, line distance, line length or package GND; tance should be as short and smooth as possible, and should not cross VCC separation line as far as possible.
3. Damping = > there are requirements for line width, line distance, line length and grouping distance; tance should be as short as possible, smooth, group by group, not mixed with other signals.
4. EMI RC circuit = > with line width, line distance, parallel tance, package GND and other requirements; according to customer requirements.
5. Other special circuits = > with line width, package GND or tance clearance, etc.; complete according to customer requirements.
6. Small power supply circuit group below 40mil = > wire width and other requirements; try to finish with surface layer, reserve the inner layer space completely for signal line, and try to avoid power signal passing through BGA area, causing unnecessary interference.
7. Pull low R, C = > no special requirements; trace smooth.
If you have PCB with BGA and need to design and layout, please contact us.