A Technique to Reduce Cross Talk Between Copper Routes Under a 1 mm Pitch BGA (WP547)

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1.0 English

This white paper describes a technique to reduce cross talk between signal routes under a 1 mm pitch BGA, without losing significant PCB real estate for outer breakout routing. The traditional BGA breakout is one BGA pin and one via to allow routing on internal layers. A typical high-speed interface at the BGA breakout using impedance controlled differential pair routing is the standard way of implementing BGA breakout of 1 mm pitch devices. By using the rule of 1 pin 1 via breakout, as shown in the following figure, and the correct selection of stack-up to allow the correct line width and pitch, it is possible to route multiple high-speed differential pairs from the BGA to any target device or connector. This technique to reduce cross talk uses multiple vias in parallel at the point of breakout. The multiple vias are arranged in such a way as to not disturb the normal routing of signals in the BGA breakout region. This is done by using smaller vias that can be fitted closer together.

Figure 1. Traditional 1 mm Pitch BGA Breakout Using a One Pin, One Via Solution