Wettable Flanks UDFN8 Automotive EEPROM Introduction

In the automotive EEPROM market, the SOIC-8 package has been the hottest for many years, if not decades. While size constraints have driven other market segments toward more compact packaging solutions, the automotive EEPROM space has gone the other way due to several factors. One factor is that in traditional automotive applications such as engine control units and powertrain systems, space constraints are not as high as the premium in portable consumer electronics applications. Another factor is that the SOIC-8 package is widely available and certified, making it very attractive to automotive OEMs that value multi-sourcing and proven practices. Finally, the DFN (dual flat no-lead) package, while taking up less space due to the lack of leads, generally does not support a critical process in the automotive manufacturing process - automatic optical inspection (AOI).

AOI is a step in PCB manufacturing where a camera automatically verifies that all components on the PCB are present and correctly soldered, and is ideal for leaded packages where both the leads and pads are visible. With DFN packages (as with any surface mount package), the contacts between the package and the pads are not visible, making AOI impossible.

Without AOI, manufacturers are likely to produce boards with intermittent or poor contact (cold solder joints) or no contact. In automotive applications where reliability is critical, the alternative is automated X-ray inspection, but this is expensive and not available on all packaging lines.

Recently, the use of electronic components in automobiles has continued to grow beyond traditional automotive applications such as power supplies and engine control. One area that has seen significant growth is Advanced Driver Assistance Systems (ADAS). Modern ADAS systems include cameras, sensors, and in-vehicle networks—applications where size is critical and DFN packaging is a good fit. But ADAS is a safety system, so reliability cannot be compromised.

To meet these needs, ON Semiconductor has introduced automotive serial EEPROMs with wettable flanks, UDFN-8.

These standard serial EEPROMs have the same pinout as the SOIC-8 type devices, but the SOIC-8 package measures 4.9 mm x 3.9 mm (excluding the pins), while the UDFN-8 package measures 2 mm x 3 mm. Unlike the standard DFN package, the wettable flank UDFN-8 supports automated optical inspection. The wettable flank UDFN has tinned pins, while the traditional UDFN has copper sidewalls. After the package sawing process, the copper sidewalls are susceptible to oxidation. This exposed copper does not form a uniform solder face fillet when the package is soldered to the board. The tinned sidewalls protect the copper and also improve the solder joint on this outer side. In addition, the wettable flank UDFN pads have U-shaped dimples on the edges. During the soldering process, the solder fills these spaces, forming detectable solder joints. This allows for easy visual inspection of the solder joint from the side of the package. ON Semiconductor Serial EEPROMs with wettable flanks in the UDFN-8 package are fully qualified to automotive Grade 1 (-40 °C to +125 °C). They are available in all three standard protocols (I2C, SPI and Microwire) and in densities ranging from 1 Kbit to 1 Mbit.