A woman walks in front of a Sharp logo displayed on an electric signboard at a railway station in Tokyo, Feb. 25, 2016. KAZUHIRO NOGI/AFP/Getty Images

Foxconn Technology Group and Sharp Corp. formally signed off on the takeover deal Saturday, after an extended period of negotiations. Foxconn had agreed to buy 66 percent stake in Japan's Sharp for 389 billion yen ($3.5 billion) Wednesday.

Foxconn chief Terry Gou formally signed a $3.5 billion deal to put Sharp Corp. under his control and promised a successful rescue of the troubled Japanese electronics maker at a packed news conference Saturday.

However, he did not give a timeline on when Sharp would become profitable again, but expressed confidence in the Japanese company's ability to bounce back with its highly regarded technology, according to Reuters.

"Everybody is saying OLED," Gou said at the event held at Foxconn and Sharp's jointly owned liquid crystal display factory in Sakai, western Japan. "If I was an engineer, I would choose IGZO," referring to Sharp's proprietary expertise in indium gallium zinc oxide display technology which is more energy efficient than the popular OLED (organic light-emitting diode) technology.

Gou accepted that the turning the Japanese display maker around would be “very hard.” "I'm not going to sugar-coat the challenges," he said. "But I have a clear roadmap in my heart."

Foxconn — formally known as Hon Hai Precision Industry Co. — already has a range of flat screen businesses, and the addition of Sharp will make it the world's top liquid crystal display (LCD) panel maker.