Atmel AT91SAM9260 Based Embedded MPU

Gideon Analytical Laboratories, Inc. received Atmel AT91SAM9260 based Embedded MPU; it is a 180 MHz ARM926EJ-S ARM Thumb Processor. The SAM9260 is based on the integration of an ARM926EJ-S processor with fast ROM and RAM memories and a wide range of peripherals. It embeds an Ethernet MAC, one USB Device Port, and a USB Host controller. It also integrates several standard peripherals, such as the USART, SPI, TWI, Timer Counters, Synchronous Serial Controller, ADC, and MultiMedia Card Interface. The SAM9260 is architecture on a 6-layer matrix, allowing a maximum internal bandwidth of six 32-bit buses. It also features an External Bus Interface capable of interfacing with a wide range of memory devices. The device was with the concern that it did not function at 50C.The device was wired up in such a way to determine the continuity from the power, ground and I/O pins at room temperature and 55C. The testing revealed that the power and some I/O pins were intermittent at 55C. The device was put on a known good PCB with full functionality and it failed. A good Atmel was installed and it worked on the same PCB without any issues. The device was decapsulated revealing the wires bonds both on the lead frame and the die. As can be seen in the photographs, the die had several ball bonds that came off during decapsulation. The coefficient of thermal expansion is greater for the molding compound than it is for the gold balls. At higher temperature, this epoxy expansion moves the ball bonds and renders them intermittent. No bond issues were noted on the interconnects to the lead frame. The bonding issue was primarily on one side of the die and primarily with one lot. This was a manufacturing issue.

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