With the increasing demand for smaller and more powerful boards, we have to understand the advancement in packaging to cater to the electrical, mechanical, and increased lifetime performance specifications. Ball Grid Arrays come with the modern technology of lightweight, small pitch, and size. The designers should brush up their knowledge in detail about the BGA packaging, as in the future we have to design boards that are high speed, high frequency, complex density interconnect boards with more than 10,12,14 and 16 layers. They all will be based on BGA packaging components
With the help of this article, we will learn about the popular BGA design guidelines, definition, functionality, challenges, and industry-proven techniques for PCB layout. Let us begin and take maximum advantage of the content to grasp information about BGA circuit board design.
What is a BGA Design?
BGA design is a surface-mount packaging technology used for integrated circuits. In BGA circuit board design, tiny solder balls are arranged in a grid at the bottom of the chip and connected to the PCB. BGA is a semi-conductor packaging type, called a Ball Grid Array. Its existence is known in the mid-1970s. It is also known to be an upgraded version of pin grid arrays. It is an SMT component. BGAs have solder balls on the bottom surface of the integrated chips. The pitch size of the solder balls can be as low as 0.5mm,04mm.
The solder balls are set in a row and column design forming a matrix. Due to the small form factor, a BGA circuit can equip 100,200 electrical connections. There are different types of BGA based on core materials like Plastic, Ceramic, Tape, Metal, and chip. BGA package is available for SoC, microprocessors, microcontrollers, and other integrated chips. They are widely used in complex designs having applications in the military, medical, space, and automotive sectors. The BGA circuit board design requires professional skill for BGA PCB layout.
BGA Circuit Board Design Guidelines and Best Practice
BGA consists of a large number of pin counts, which are in the shape of the ball, with no leads, and no SMT pads. We utilize multiple layers only for providing routing traces to BGA chips. When we take on BGA PCB designs for complex applications, the main controller or processor comes in BGA packaging. BGA circuit board design needs prior experience to handle the layout. The calculations and guidelines are difficult. Here we will discuss the plan and pre-design steps in detail for handling BGA packaged components.
1. Pre-Planning Steps
Fixing the BGA packaged integrated circuit during component placement at the BGA PCB design beginning is not an optimized approach. We have to start with the pre-planning phase first where we begin to check the largest pin count BGA used in the circuit, in terms of size and I/Os. This selection of BGA will determine how many layers are required in the layer stack-up planning of the PCB. With stackup in the BGA PCB design, we determine the conductor width of traces to match the target impedance values.
2. Define the Placement Plan
Floorplanning means component placement at the beginning of the PCB layout design stage.BGA pins require a placement plan in such a way that their routing can be optimized when setting about BGA PCB design. Its routing takes up a lot of space. BGA has very fine pitch solder balls. Placing the fixed parts like connectors, and screws earlier than BGA will assist in the BGA routing strategy. BGA generates heat during signal flow and needs an air gap to throw out heat away from other power components.
3. Signal & Power Integrity
After the BGA location is decided on the board placement. We start to project the different routing strategies for BGA PCB layout design that will provide improved signal integrity and power integrity.BGA pins require shorter trace lengths, via in-pads, and thermal vias, due to heating. We know that high-speed digital signals should be placed close to the IC pin to avoid EMI and noise added to the signal. Motherboards are one example that has processors, fast memory ICs, and high-speed communication ICs. BGA packaging is found in motherboards. High processing speed requires more power and heat, so the fanout BGA PCB design strategy deployed should assist in keeping the signal close to off-board connectors
4. Employ Filtering Circuit
In High-density boards we have multiple power rails, the analog section should be away from the BGA circuit board design section. Analog signals carry distortion, noise, and radiation. When BGA logic signals come in closer contact, the logic clock signal gets debouncing issues. We should use many bypass or decoupling capacitors in parallel to remove the frequency component in digital signals.BGAs are very sensitive to noise and distortions. Keep the capacitors close to the input pins of BGA when we consider the signal output in the BGA PCB design.
5. BGA Entry & Exit Route
Routing any fine-pitched BGAs requires planning the escape route and a detailed discussion with the manufacturer. Because in the BGA PCB design process, we cannot visually inspect the issues that occurred in the soldering process, rework is complicated. BGA ICs layout carry high-speed signals that need enough clearance from each other to avoid the cross-talk noise.
It is recommended to begin with the outermost BGA pins and diagonally design the traces in the BGA PCB layout. After that step of BGA circuit board design, inner rows of pins can be routed using multiple microvias.
6. Dog-Bone Method
It is a standard approach to manage the multiple traces exiting from a BGA circuit board design. Traces are divided into four quadrants of a BGA section for easy mode. A small length trace is attached to via making the shape of a dog and bone. It is a better technique than via-in-pad, given that the pitch of the BGA pins is near 0.8 or 1mm
7. Managing Power in BGA PCB Design
BGA pins have multiple pins linked to power and ground. Different voltage rails have to be connected with different power supplies on the board. Layer stack-up should have 2 layers dedicated to power planes and ground planes with other inner layers. The ground plane in the BGA PCB design should be placed closer to the power plane to provide the smallest return path. It provides good power integrity. We can also add polygons on the group of pins connected same voltage level. In that case, via placement on the board should also be taken care of.
8. BGA Circuit Board Design Rules
Based on the pitch size, we have to select which type of via (through hole, blind/buried, micro via, via-in-pad) style to be adopted. Differential pairs are a must-have in high-speed boards. We should define the net classes, trace width, via size and clearance classes specific to a group of pins in the BGA PCB design rule manager before we jump to the layout
9. Heat Management
An increase in the temperature during current flow in BGA circuit board design is a normal scenario. As BGA operates with high-power processing. While we decide the via fanout to avoid the blockage of signals. It is important to incorporate thermal pads and thermal vias also to remove the excess heat from power and ground plane layers. We should add via stitching to planes to ensure heat management after the BGA PCB design. Ensure thermal runaway does not happen in the soldering and assembly process too.
10. Soldering Strength
Once the BGA circuit board is fabricated, it is taken to the reflow machine. We should follow the datasheet soldering profile for BGA parts because the inspection is challenging for BGA parts, only X-ray machines can be used. It is better to ensure that the solder joints are strongly bonded and that vibrations or shocks do not break the joints. We can pre-check the BGA in simulation and verify the stability.
Summary
BGA boards are already a popular choice in today’s electronics world. The engineers need to make the design and layout learning guidelines critical. BGA PCB layout design is time-consuming even with the guidelines and steps followed. Discussion with the project management plays a crucial role in prior information on timelines, cost considerations, and challenges. It will be helpful to maintain the customer specifications and create an impactful BGA PCB design. BGA is a part of future advancement.
