Failure Analysis on TI TMS320F28335PGFA DSP

Gideon Analytical Laboratories received a TI TMS320F28335PGFA Digital Signal Processor for failure analysis. Digital Signal Processing applications include audio and speech processing,sonar,radar, and other sensor array processing,spectral density estimation,statistical signal processing,digital image processing, among many others. The TI TMS320F28335PGFA features high-performance static CMOS technology, a 32-bit CPU, 16 x 16 and 32 x 32 MAC operations, and Harvard bus architecture. It has up to 88 individually programmable, multiplexed GPIO pins with input filtering. We were advised to pay special attention to pins 141 and 148 because they were possibly nonfunctional in operation.

Failure analysis ensued. The TI TMS320F28335PGFA DSP was cross-sectioned, and micrographs were taken of problem areas. Many of the leads showed corrosion by-products. The corrosion attacked the lead pads by allowing moisture ingress through the conformal coating, which was inappropriately applied. We took micrographs of the problematic leads. SEM-EDS analysis and curve tracing were used next. The two pins above were shorted to Vss. The epoxy package was milled out, and acid used to etch the DSPs to access the die inside. The die was then decapsulated to investigate. Micrographs and radiographs were taken of the die, which yielded some impressive results. The conformal coating had holes along with the lead toes and elsewhere. The corrosion material was conductive, showing metal and high amount of moisture. This failure appeared to be environmentally induced. The mystery of why the TI TMS320F28335PGFA DSP was failing was solved.

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Leads showing corrosion by-products

Leads showing corrosion by-products

X-ray of the DSP, still mounted to PCB

X-ray of the DSP, still mounted to PCB

Ball bond still on pads on the die, note the area in red ellipse.

Ball bond still on pads on the die, note the area in red ellipse.

Die after decapsulation

Die after decapsulation

Milling out the DSPs

Milling out the DSPs

Curve trace after removing conformal coating and corrosion

Curve trace after removing conformal coating and corrosion

Micrograph of top of the leads where analysis was made

Micrograph of top of the leads where analysis was made

SEM-EDS of corrosion

SEM-EDS of corrosion

Corrosion attacking the lead pads

Corrosion attacking the lead pads