DDi Corp. stockholders have approved a pending sale to a St. Louis-based competitor, the company announced on Thursday.

The Anaheim-based circuit board maker is set to be acquired for $268 million by Viasystems Group Inc., ending its 12-year stint as a Nasdaq-listed stock.

The transaction, subject to customary closing conditions, is expected to finalize in the next week.

The deal price represents a 20% premium on DDI’s average share price for three months prior to the announcement in early April.

Terms of the agreement have been unanimously approved by the boards of both companies.

DDi makes circuit boards that later are assembled with chips. The boards go inside equipment for aerospace, military, industrial, medical, networking and communication uses.

It built its name in the industry by turning around boards quickly, especially on prototypes.

Most of the company’s orders are completed in less than 10 days, sometimes within 24 hours.

Viasystems, which trades on the Nasdaq under the VIAS ticker, was attracted to DDi because of its strong position in the military and aerospace market, and the growing industrial and instrumentation market.

DDi’s saw $263.3 million in revenue in 2011.

The company employs about 360 workers in Anaheim and 1,600 companywide. It also has manufacturing operations in Milpitas, Virginia, Ohio, Colorado and Canada, and a data center in Texas.

Neither DDi nor Viasystems has commented on the potential effects of the deal on OC operations.

The combined company is expected to have annual revenue of $1.3 billion and employ 15,650 people.

Investors pushed Viasystems shares up more than 3% on Thursday to a market value of about $390 million.

DDi shares traded relatively flat throughout today’s session on a market value of about $267 million.