Introduction

Reducing or eliminating supply shortages within a production flow is essential for many customers. When supply issues arise, customers typically must redesign their boards to accommodate a new package for a given device, forcing customers to push production dates and miss crucial deadlines. However, with TI's expanded small package selections and dual footprint configurations, supply constraints can be reduced. Dual footprint board layout techniques can help mitigate the impact of component shortages by enabling a design to use different package options for a given component.

This application brief covers multiple common package families and provide guidance on how to select a dual footprint.

Dual Footprint Solution using TI's Various Packages

A dual footprint is a footprint which can be used with two or more device packages, with minimal to no routing adjustments, eliminating the need for last minute board redesigns or spins. TI offers a variety of packages for both leaded and non-leaded types. Table 1 shows a few examples of popular packages from TI, while a full list can be found in Find TI Packages. TI's level shifter portfolio contains many of the packages listed below and includes devices under Auto Directional, Direction Controlled and Fixed Direction categories for Industrial, Automotive, and High Reliability applications.

With TI's packages being among the industry's smallest, implementing dual footprint layouts for leaded and non-leaded packages is simple given that many of these packages have the same orientation and pinout.

Leaded to Non-Leaded Packages

To create a dual footprint design, the board designer must place the smaller non-leaded package in the center of the larger leaded package, and connect the corresponding pins. This allows either package to be placed on the footprint. Figure 1 shows some examples using TSSOP and QFN packages, while Figure 2 shows some examples using smaller packages like SOT-23 and SOT-SC70 with X2SON and USON. Many level translators use the packages shown in the following examples, and Table 2, Table 3, and Table 4 give the full list of TI devices and the corresponding footprint configurations the devices can support.

Figure 1 TSSOP Package Layout With QFNs

Figure 2 SOT-23, SOT-SC70 Package Layout With X2SON, USON

Design Consideration

Make sure proper spacing is used when designing a dual footprint layout. Most manufactures follow a 0.1 mm (approximately 4 mil) design rule for spacing between each pad. If such a rule is not followed, there will be insufficient or no space for solder mask to fill between pads of the layout. A lack of solder mask can cause the device to shift, resulting in shorted or floating pins.

Conclusion

Using TI's numerous package options, customers can easily design dual footprint layouts for multiple components which can dramatically reduce the chances of missing delivery deadlines that can result from component supply shortages. Dual footprint layout considerations can be a vital tool for design engineers as they select and design in components that are resilient to supply chain disruptions. Customers can use the previous examples to provide an effective second source and future-proof their design.