What Causes BGA Crosstalk?
BGA packages are noted for their compact size and high pin density.
The type of signal crosstalk that results from ball arrangement and misassignment in BGA packages is called BGA crosstalk.
BGA crosstalk is dependent on the position of the aggressive signal and the victim signal in the ball grid array arrangement.
A low crosstalk BGA arrangement is essential for reducing BGA crosstalk
The level of integration is increasing exponentially in integrated circuits with numerous gates and pins. Fortunately, the development of ball grid array (BGA) packages makes these chips more reliable, robust, and convenient. BGA packages have a reduced size and thickness as well as a higher pin count. However, BGA crosstalk limits the application of BGA packages by significantly impacting signal integrity. Let’s discuss BGA packages and BGA crosstalk a little more.
Ball Grid Array Packages
BGA packages are surface-mount packages that use tiny metallic conductor balls to mount integrated circuits. The metallic balls form a grid or matrix pattern and are arranged underneath the chip surface to make connections with the PCB.
Components using BGA packages do not have pins or leads across the periphery of the chip. Instead, ball grid arrays are arranged at the base of the chip. These ball grid arrays, called solder balls or solder bumps, act as the connectors in BGA packages.
Microprocessors, WiFi chips, and FPGAs often utilize BGA packages. In BGA package chips, solder balls allow the flow of current between the PCB and the package. The balls are physically connected to the semiconductor substrate of the electronic component. The wire bonds or flip chips are used to establish the electrical connection with the substrate and the die. The conductive traces are inside the substrate that allows electrical signal transmission from the bonds between the die and the substrate to the bonds between substrate and ball grid arrays.
BGA packages distribute connection leads underneath the chip in a matrix pattern. This arrangement provides more lead count in BGA packages compared to flat and dual-in-line packages. In a leaded package, pins are arranged around the perimeter. Each pin on the BGA package is provided with a solder ball, and the balls are on the undersurface of the chip. This undersurface arrangement provides more area, which makes more pin counts, less congestion, and less shorting of the leads possible. In a BGA package, the solder balls are arranged at the farthest distance from each other when compared to leaded packages.
Advantages of BGA Packages
BGA packages offer compact size and high pin density. The low inductance of BGA packages allows the usage of lower voltages. The well-spaced arrangement of ball grid arrays makes the alignment of BGA chips to PCBs easier. Some other advantages of BGA packages are:
- Good heat dissipation due to the low thermal resistance offered by the package.
- The length of the leads in a BGA package are shorter than leaded packages. High lead counts along with small sizes make BGA packages more conductive, which improves their performance.
- BGA packages offer high performance at high speeds compared to flat and dual-in-line packages.
- The manufacturing speed and yield of PCBs increase when using components in BGA packages. The soldering process becomes easier and more convenient, and BGA packages allow for easy re-work.
BGA packages do have some disadvantages: the inability of solder balls to flex, difficulty in inspection due to high package density, and the need for expensive soldering equipment for large production. BGA crosstalk is another limitation that impacts the signal integrity of the signals transmitted over BGA packages.
BGA packages are often utilized in high I/O devices. The signals transmitted and received by the integrated chips with BGA packaging can be disturbed by the coupling of signal energy from one lead to another. Signal crosstalk that results from ball arrangements and misassignments in BGA packages is called BGA crosstalk. The finite inductance between ball grid arrays is one of the reasons for crosstalk effects in BGA packages. When there is a high I/O current transient (aggressive signal) in BGA package leads, the finite inductance between the ball grid array corresponding to the signal pin and return pin creates voltage disturbances on the chip substrate. This voltage disturbance leads to glitches in the signal and is transmitted out of the BGA package with noises that result in crosstalk effects.
In applications such as networking systems with thick PCBs utilizing through vias, BGA crosstalk is common if there are no measures taken to shield vias. In such circuits, long-through vias placed underneath BGAs cause a high amount of coupling and create significant crosstalk interference.
BGA crosstalk is dependent on the position of the aggressive signal and the victim signal in the ball grid array arrangement. A low crosstalk BGA arrangement for packages is essential for reducing BGA crosstalk. Cadence software offers tools for designing BGA packages prone to low crosstalk. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts.