MPUs & MCUs
consumer applications including digital cameras, printers and routers. The next diagram (Figure 4) shows an example PCB layout using the Open Array BGA. Here you can see the main advantage of this package. Whilst still offering a high density of available I/O, with 100 balls in a 7 x 7 mm2
package, the RA4L1 offers
an open grid or missing ball arrangement where there are spaces in the grid to allow easy escape for routing the device on lower cost PCBs.
Figure 3: Comparison of LQFP and BGA packages
design rules, both in terms of PCB layout and PCB material, as well as stricter requirements for the equipment needed to manufacture products using this package type. Figure 3 compares the internal design of a typical BGA package and a typical LQFP package. Here you can see one of the advantages of using a BGA package. Inside the BGA package, the die is mounted on a small substrate, this means that some additional internal connections can be managed in a BGA, so often additional I/O pins are available to the user for the same ball count. This can be seen in the BGA64 package of the RA4L1 microcontroller, which has more I/O available than the LQFP version. BGA packages can offer several advantages over traditional surface mount packages. BGA packages, with their grid of balls, typically offer higher I/O density than other
Figure 4: Example layout using a BGA100 Open Array
package types. A typical 100-pin LQFP package with a similar number of I/Os would typically be 10 x 10 mm2
twice the PCB area to mount.
One of the biggest advantages of a BGA package is its compact size, which takes up far less PCB real estate than traditional package options. BGA packages are more robust than traditional packages such as QFPs because the solder balls distribute mechanical stress more evenly throughout the package. This can reduce the effect of vibration and shock on the package, making BGA packages an appropriate choice for many applications where such stresses may occur. BGA packages typically have shorter electrical connections between the die and the balls of the package, resulting in reduced signal delays and better high frequency characteristics. This can be particularly
, requiring more than
important where the design is sensitive to the electrical environment. Due to the large surface area of the solder balls used in a BGA package, the package has better thermal dissipation than traditional packages.
Before deciding to use a BGA package, we should also consider the disadvantages of using a BGA package: Lack of solder ball flexibility. The manufacturing process for BGAs can be more expensive as it often requires additional equipment, and the number of facilities capable of manufacturing with BGA packages can be limited, although the number is growing. Testing and inspecting the solder joints of BGA packages is difficult and may require expensive equipment such as X-ray machines or extra care in the design of test routines to ensure that the device is soldered correctly. The use of BGA packages can make prototyping more difficult, as they require a full production line to produce a prototype run, and making changes is often not as easy as with traditional package options. The 100 Ball BGA Open Array is designed to provide all the benefits of a traditional BGA package, but with an open array that is easier to route than a design using a full grid BGA package. This allows the user to use cheaper two- or four-layer PCBs rather than the six- or eight-layer PCBs typically required to fully route a 100 ball BGA package. This open array option makes this version of the RA4L1 ideal for applications that require small package sizes but are also extremely cost sensitive, such as
www.cieonline.co.uk
In the diagram you can see part of a routing design showing the routing of the top layer tracks of the PCB in red and the vias and tracks required on the bottom layer of the PCB in green. As you can see, the gaps in the array make this design easier to route, as each ball on the package has room to be routed without any special technology or the use of microvias under the balls.
This type of design makes PCB routing much easier and allows the use of cheaper PCB materials.
In this article we have tried to explain the advantages of using BGA packages in a microcontroller design. The designer needs to consider both the advantages and disadvantages of using the package, not only at the design stage, but throughout the product lifecycle, as the device is manufactured and reworked if necessary. A BGA package can provide a compact solution where size is an issue, but a high number of I/Os must be maintained. The RA4L1 combines the use of compact package technology with a high- performance Cortex M33 core and powerful on-chip peripherals. Hopefully this article has explained a little about the range of compact package options available, and the benefits of using each of them, particularly the 100-ball BGA Open Array package. To find out more about the features of the RA4L1 and the compact package options available for this device, including the BGA options and the BGA Open Array package, please visit our website at:
www.renesas.com/RA4L1
You will also find a useful application note describing our recommended PCB layout guidelines. This document is intended to help those who are more familiar with LQFP packages and are interested in learning more about BGA packages with a view to possibly using them for the first time. This document is available on the Renesas website at:
https://www.renesas.com/en/document/ apn/board-design-guideline-bga- products?r=469286
Components in Electronics April 2025 43
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