A Beijing engineer who stole trade secrets from Ford worth an estimated $100 million has been sentenced to six years in a United States federal prison.

Yu Xiangdong, also known as Mike Yu, worked for the automaker as a product designer from 1997 to 2007. He was arrested after a tip off from his girlfriend.

At his trial in Detroit, Michigan, the 49-year-old admitted taking about 4,000 sensitive documents detailing engine and electrical power systems, as well as other vital components, before leaving to work for a rival Chinese company. The court heard Yu even e-mailed his resignation from China.

FBI agents took him into custody at a Chicago airport in 2009 when he arrived on a business trip. Incriminating documents were later found on his laptop.

Yu's girlfriend contacted Ford executives a year earlier to warn them Yu was providing stolen documents to potential employers in a bid to get work.

The company described the information in court as the "DNA" found in all its vehicles.

In sentencing on Tuesday, US District Judge Barbara McQuade said: "We will vigilantly protect the intellectual property of our US automakers, who invest millions of dollars and decades of time in research and development to compete in a global economy. Those who do not play by the rules will be brought to justice."

Yu was ordered to pay $12,500 in fines. He will be deported to China once he has completed his prison term.

Little is known about Yu's work and private life, but he was said to have also worked for Foxconn in 2005, while simultaneously being employed at Ford.

Following his employment with the US auto giant, he held positions at Shanghai Automotive Company and Jianghua Motors in Anhui province, before being hired by Beijing Automotive Company in 2008.

Calls to Beijing Automotive went unanswered on Wednesday.

After Yu's arrest in 2009, the company released a statement distancing itself, saying he had only worked there for several months and was on leave when he traveled to the US.