[FAQ] SN74HCS595-Q1: How do Wettable Flank WQFN packages (WBQB) help LOGIC automotive customers?

Efficient Automated Optical Inspection (AOI) with new TI LOGIC Wettable Flank devices

               Looking at the automotive market today, there continues to be growing trend towards smaller PCBs for a wide variety of applications. Though it has become apparent more recently, the simple fact is that board space comes at a premium, which has driven demand for non-leaded package options for many popular LOGIC functions such as shift registers, gates, and buffers.

               This seems like a valid solution as non-leaded packages typically have smaller footprints, but it creates a problem for automotive customers attempting to qualify these parts. Due to the nature of the solder between the board and the QFN package, it is difficult for standard camera-based AOI (Automated Optical Inspection) to fully “see” the quality of the soldered connection and qualify the part. Instead, advanced, expensive, and difficult to maintain X-ray technology must be utilized in order get a visual on the solder quality, which is not optimal and sometimes not an option for automotive customers.

Figure 1: Commonly Used WQFN Non-Leaded package and pinout for 595 (shift register) function

Figure 2: Dual footprint visuals, comparing PW (TSSOP-14 pin) and BQA (WQFN-14 pin) packages. The non-leaded BQA (WQFN) package takes up approximately 30% less board space

The solution to the issue of qualifying non-leaded packages is the wettable flank modification. A wettable flank is typically a dimpled or step cut package modification, which creates an opportunity for the solder to readily form side fillets after soldering. This allows AOI to better view the soldered connection, and qualify the part in an efficient and cost-effective manner.  

Package view	BQB0016A (standard WQFN pkg) - BQB	BQB0016B (WQFN pkg with WF modification) - WBQB
Top View
Side View

Figure 3: Side by side WQFN packages, highlighting wettable flank dimple cut modification (595 function)

Figure 4: Visual of how Wettable flanks allow for optimal AOI inspection for nonleaded packages

               Here are some examples of the new LOGIC AEC-Q100 qualified devices that have the wettable flank package modification, ensuring efficient inspection by AOI. The “BQB” in the orderable part number is indicative of the WQFN (Very Very Thin Quad Flat No Lead) package, while the “W” represents the device having the wettable flank modification/capability. Feel free to click on the WF OPNs below for more information and datasheets.

References and further information on new TI LOGIC packages

SN74HCS595-Q1 datasheet – TI

Optimizing Board Design for Supply Constrained Environments - (TI Applications)