With increasing demand for compact electronic devices with greater functionalities, PCB designers are turning more and more to ball grid arrays (BGAs). There are numerous benefits to using ball grid arrays; for example, the close alignment of solder balls reduces footprint area, strengthens interconnections, and reduces signal distortion. Moreover, BGA packages come with in-built thermal vents that significantly reduce the chances of overheating.
However, working with BGA packages may seem overwhelming to a new designer. BGA packages may come with different pitch sizes (the distance between two consecutive balls). With a decreased pitch size, the routing challenges for PCB routing increase. That's why it is imperative to understand the ideal PCB layout recommendations for BGA packages. Doing so can ensure board manufacturability without exhausting your budget.
Best PCB Layout Recommendations for BGA Packages
A BGA features an array of solder balls arranged in a uniform pattern on the bottom of a component, typically in an integrated chip. It can directly affect the signal integrity and manufacturability of your board.
Below are some essential PCB layout recommendations for BGA packages that you should always consider when designing a PCB.
- BGA Landing Pads
BGA landing pads usually refer to the exposed metal area of the PCB to which the components are soldered to. A combination of such pads is referred to as the component footprint, or the landing pad. While designing footprints for BGA components, it is often advised to opt for Non-Solder Mask Defined (NSMD) landing pads instead of Solder Mask Defined (SMD) landing pads. The former provide a large copper surface area for solder ball connections and more clearance between the pads. As a result, it is easier to achieve wider trace width and more flexibility in the use of vias.
- Layer Count Estimation
For successful BGA routing, the first step is to calculate the number of layers needed to remove the signal pins. A general equation for calculating the number of layers is:
Routing channels indicate the number of available routing paths from the BGA paths. For a BxB grid BGA (where B = number of pins on one side), the total number of routing channels is B² -1. Routes per channel indicate the total number of routed signals between pads—either one or two.
- Layer Count Optimization
The number of layers required for well-optimized routing primarily depends on the number of pins, fixed pinouts, pad size, pad pitch, and trace width. The number of signal layers increases with BGA size. Additionally, pad size, pad pitch, and trace width determine the number of layers required to route one or multiple signal rows between the BGA pads.
The word “via” here represents the drilled holes between two or more layers of the PCB that create an electrical conductive path. The holes are filled with non-conductive materials to avoid solder inflow from the pad. Vias are incorporated on the BGA pads to reduce the number of layers needed to route a design. Though it preserves the number of layers, filling holes up with non-conductive material demands additional cost and time. Moreover, they need additional space on the board.
However, you can opt for a via-in-pad design (VIP design) to overcome that challenge. It is a popular choice as it enables you to achieve a small hole diameter with a smaller drill depth between the top side and subsequent layer. However, it involves time-intensive procedures such as plating the holes, filling them with epoxy, and covering the entire via with plated copper. Thus, it is advised to skip via-in-pad designs if you are on a tight deadline to build the prototype.
DFM for HDI Printed Circuit Boards
Your CM can help you decide whether to go with traditional vias or a via-in-pad design with respect to your application requirements.
- Maximum Board Thickness
The maximum thickness of the board depends on two major factors: minimum drill diameter and aspect ratio. A typical aspect ratio of 10:1 indicates that the board will be 10 times thicker than the drill diameter. A board with a 14mil drill diameter would have a maximum board thickness of 140 mils. If more thickness is required, going for buried or blind vias would help, but at a higher manufacturing cost.
- Routing Advice
While working with BGA components, routing is a challenging affair. Once the components start to sink after soldering, the space for through-vias narrows with decreasing pin-pitch and pad size. Even with the smallest possible drill and pad, there is a chance that a breakout will occur that involves overlapping one or more holes at the edge of the pad. In worst-case scenarios, it may lead to cracks and open circuits—lowering board reliability and necessitating additional expenses for unwanted board reworks.
One of the best ways to avoid the hassle is to incorporate BGA dogbones into your design. This process involves using a teardrop that helps extend the pad size in the direction of the trace without any additional cost or layout space.
Some CAD tools can't add teardrops to your design. In such cases, it is imperative to have your CM add them for you.
|Tempo's Custom PCB Manufacturing Service
Tempo Automation can help you select the best BGA routing to retain board signal integrity while reducing manufacturing costs. As we consistently implement best practices and strictly follow design guidelines, the manufacturability of your board is always our top priority.
Our automated turnkey PCBA manufacturing process leads the industry in quickly delivering high-quality boards that meet the flexibility and reliability requirements of semiconductor evaluation/test boards for prototyping and on-demand production. It includes deep collaboration with your engineers when needed and can furnish information for DFM checks as downloadable DRC files in Altium Designer, Cadence Allegro, Mentor Pads, other CAD formats, and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on CAD files or how to incorporate your design into a CAD format, contact us.