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BGA PCB Board Design – Key Considerations

BGA PCB Board Design - Key Considerations

The BGA PCB board is an integral part of modern-day electronics. It incorporates the BGA package, which attaches microchips to the substrate using a grid-like pattern of solder balls. This board type can be difficult to produce, given the numerous pin connections and fine pin pitch. Below, we share its design tips.

What is a BGA in PCB?

BGA stands for “Ball Grid Array”. It refers to a surface mount IC package comprising an array of solder balls in a grid pattern on its bottom. The solder balls melt to permanently it to a printed circuit board.

The BGA package replaces the pin-based PGA (Pin grid array) format. Instead of solder balls, the PGA is attached to the PCB using pins on its sides.

BGA packages provide more connections in a small space (from a few to hundreds or even thousands). It offers the following advantages when used on a printed circuit board

  • Reduced PCB footprint and higher component density
  • Shorter connections that improve electrical performance
  • Reduced signal distortion since the distance between the package and PCB is drastically reduced
  • Enhanced heat dissipation due to the lower thermal resistance between the array and the board
BGA circuit board design showing fan-out strategies
BGA circuit board design showing fan-out strategies
Resource: https://hackaday.com

BGA Circuit Board Design

The BGA PCB board requires more effort to design than a standard board; you need to use thinner traces and smaller vias to route it, which can be challenging to implement.

Furthermore, you must ensure efficient thermal performance, inspectability, and other functionalities, such as avoidance of signal degradation or power transmission issues.

The designer must meet varied specifications, or the board may experience problems later. The next part discusses the most important considerations when designing this board type.

Designing a simple ball grid array board
Designing a simple ball grid array board
Resource: https://hackaday.com

BGA PCB Design Guidelines

As we have seen, proper design is critical when placing a ball grid array on a printed circuit board. Improper practices can lead to issues requiring rework and increasing production costs. Several BGA rules apply. They include the following.

Array Design and Type

Ensure the array fits the board size or required footprint. The distance between pads varies but generally ranges from 0.8mm to 1 mm. Some use solder mask-defined pads, while some do not.

Different types of BGAs are also available. Depending on your specific application, determine the array that suits your needs. Options include plastic, ceramic, micro and micro-fine BGA, stack BGA, and lead or leadless types.

BGA PCB Pad Size and Shape

Most circuit boards with ball grid arrays conform to the IPC class 3 standards, which impose strict reliability levels. That means higher tolerances and specified solder mask and annular ring features.

Use the size of the solder balls to determine that of the pads. Determine whether the solder mask defines the pads or not, too.

For better results, use round pads. These wet more effectively, allowing excellent soldering for secure connections compared to rectangular pads.

BGA PCB Stack-Up

The number of layers in the BGA substrate mainly depends on the number of signal layers needed and other factors, such as whether there’s a need for controlled impedance.

Consider the distance between the solder balls or pads when determining the layer count. The finer the pin pitch, the higher the likelihood that you will need more layers to route the array.

Use ground planes below the array to separate power and signal layers for controlled impedance, placing a dielectric layer between them.

BGA PCB Routing

Good routing practices ensure better performance and optimized signal transmission. This board requires routing exit traces through closely packed pin rows, which can be challenging.

When placing exit route or fan-out traces, begin with the outermost rows. These are generally easier to route. Difficulties start to emerge when you get into the inner rows.

The dog-bone fan-out method may suffice if you are routing large pin pitches but not when routing closer pins. The via-in-pad technique is more applicable for smaller pitches less than 1 mm apart.

Use equal trace lengths to optimize signal transmission. Because BGA PCB routing typically involves high-speed signal, ensure adequate trace spacing to avoid crosstalk.

Thermal Considerations

The integrated circuit components of a ball grid array generate a lot of heat during use. The heat must effectively dissipate. And while the technology allows efficient heat loss, additional measures are usually required.

Match the thermal properties of the BGA substrate with those of the ball grid array to avoid a CTE (Coefficient of Thermal Expansion) mismatch.

Use large copper planes to enhance heat loss and include thermal vias to conduct heat vertically. Place heat sinks to help dissipate heat as required.

Mechanical Stress

The solder joints of the BGA assembly must be structurally sound. Determine the use conditions, such as mechanical shock and vibrations, and plan accordingly.

Perform a thorough evaluation to ensure the array connections meet required stability standards. Simulating the reflow process and identifying stress points can help validate your design.

Inspectability

The ball grid PCB assembly poses inspectability challenges, given the hidden nature of its solder ball connections. These are addressable during the design stage, where you minimize inspection and testing constraints as required.

Incorporate test sockets and contacts for tester probe connections. In some instances, vias can act as test connections, even though it isn’t advisable due to the risk of their damage.

Cost Considerations

To minimize costs, implement measures like reducing the number of layers and using less expensive production methods. For example, automation offers speed and accuracy but can increase manufacturing expenses.

Inspection technologies like X-rays provide better coverage but cost more. Electrical testing, such as the boundary scan method, may suffice instead.

Only be sure to balance cost optimization and the application requirements. These measures are only suitable for small-volume productions with lower reliability needs.

Ball Grid Array packages on a computer motherboard
Ball Grid Array packages on a computer motherboard
Resource: https://www.youtube.com/watch?v=yqYgB6N2ijM

What are the Applications of the BGA PCB Board?

The BGA PCB board has numerous uses in the world of electronics. It forms an essential part of consumer electronic gadgets like mobile phones, tablets, and game consoles.

Computer and server motherboards or CPUs are typically BGA boards. Other applications include automotive PCBs like car computers and other circuit boards.

Telecommunication systems also employ HDI boards with ball grid arrays. Various medical technology devices and systems use it, too. Other applications include the electronic systems of manufacturing plants.

High-end systems that use the BGA circuit board include military and aerospace. The board is designed to higher standards, providing robust connections and better signal and power transmission characteristics.

BGA PCB board rework-station
BGA PCB board rework-station
Resource: https://www.youtube.com/watch?d6iGqyBsHxQ

Future Trends in BGA PCB Design and Manufacturing

With the continued move toward miniaturization technologies, we’ll likely witness changes to the BGA PCB board over the next few years. Components are becoming smaller, and ICs are more powerful.

Plus, with the introduction of 5G networks and other communication technologies, the BGA circuit board will find even more applications since it packs more power in a small area.

The BGA package will become better in the coming years. It will also become more reliable with newer IC technologies and higher-quality materials that withstand different usage conditions.

Conclusion

The BGA PCB board is crucial in many applications today, from mobile phones to the more complex electronics used in military and space exploration. Its proper design requires a thoughtful consideration of various factors, as discussed in this article.

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