TAIPEI -- Unimicron, the world's largest printed circuit board manufacturer, has purchased the outstanding shares of Ruwel International from investor group BlueBay.

Unimicron already owned 35% of Ruwel following an investment in fall 2009. At that time, BlueBay also had acquired a majority stake in Ruwel.

Unimicron has 14 production facilities in Asia and employs more than 20,000 workers. The PCB maker had revenues of $2.1billion in 2001, making it the largest in the world, slightly ahead of No. 2 Ibiden according to Dr. Hayao Nakahara's annual NTI 100.

Ruwel employs 225 workers and has annual sales of about $73 million. It is one of Europe's 10 largest PCB fabricators.

According to the companies, Ruwel's plant in Geldern, Germany, will become an R&D and process development site, from which product will be ramped to volume at one of Unimicron's facilities in Asia. Ruwel's management will remain intact, the firms said.