UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 4, 2014

TTM TECHNOLOGIES, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (714) 327-3000

(Former name or former address if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

On December 4, 2014, TTM Technologies, Inc., a Delaware corporation (“TTM” or the “Company”), received a second request for additional information and documentary material (the “Second Request”) from the Federal Trade Commission (the “FTC”) in connection with its review of the pending acquisition of Viasystems Group, Inc., a Delaware corporation (“Viasystems”), by the Company (the “Merger”). Issuance of the Second Request extends the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 until 30 days after the Company and Viasystems have substantially complied with the FTC’s Second Request, unless the waiting period is extended voluntarily by the parties or terminated earlier by the FTC. The Company and Viasystems intend to cooperate fully with the FTC.

On December 4, 2014, the Company and Viasystems issued a joint press release announcing that they each had received a Second Request from the FTC. A copy of the joint press release is attached hereto as Exhibit 99.1.

(d) Exhibits.

Forward-Looking Statements

Certain statements in this communication may constitute “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements relate to a variety of matters, including but not limited to: the timing and consummation of the proposed merger; the ability of the parties to consummate the proposed merger and the satisfaction of the conditions precedent to consummation of the proposed merger, including the ability to secure regulatory approvals in a timely manner or at all; and other statements that are not historical fact. These statements are made on the basis of the current beliefs, expectations and assumptions of the management of TTM and Viasystems regarding future events and are subject to significant risks and uncertainties, many of which are beyond the control of TTM or Viasystems. Such statements are predictions, and actual events or results may differ materially.

Additional factors that may cause results to differ materially from those described in the forward-looking statements are set forth in the Annual Report on Form 10-K of TTM Technologies, Inc. for the year ended December 30, 2013, which was filed with the Securities and Exchange Commission (the “SEC”) on February 21, 2014, under the heading “Item 1A. Risk Factors” and in the Annual Report on Form 10-K of Viasystems for the year ended December 31, 2013, which was filed with the SEC on February 14, 2014, under the heading “Item IA. Risk Factors,” and in each company’s other filings made with the SEC available at the SEC’s website at www.sec.gov.

Neither Viasystems nor TTM undertakes any obligation to update any such forward-looking statements to reflect any new information, subsequent events or circumstances, or otherwise, except as may be required by law.

Additional Information and Where to Find It

This communication may be deemed to be solicitation material in respect of the proposed Merger between the Company and Viasystems. The Company has filed with the SEC a registration statement on Form S-4, which includes a prospectus with respect to the Company’s shares of common stock to be issued in the proposed Merger and a proxy statement of Viasystems in connection with the proposed Merger (the “Proxy Statement/Prospectus”). The Proxy Statement/Prospectus was sent or given to Viasystems’ stockholders when the Proxy Statement/Prospectus was declared effective by the SEC, and it contains important information about the proposed Merger and related matters. VIASYSTEMS SECURITY HOLDERS ARE ADVISED TO READ THE PROXY STATEMENT/PROSPECTUS CAREFULLY BECAUSE IT CONTAINS IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. The Proxy Statement/Prospectus and other relevant materials (when they become available) and any other documents filed by the Company or Viasystems with the SEC may be obtained free of charge at the SEC’s website at www.sec.gov. In addition, security holders will be able to obtain free copies of the Proxy Statement/Prospectus from the Company or Viasystems by contacting either (1) Investor Relations by mail at TTM Technologies, Inc., 1665 Scenic Avenue, Suite 250, Costa Mesa, CA 92626, Attn: Investor Relations Department, by telephone at 714-327-3000, or by going to the Company’s Investor Relations page on its corporate website at www.ttmtech.com, or (2) Investor Relations by mail at Viasystems Group, Inc., 101 South Hanley Road, Suite 1800, St. Louis, MO 63105, Attn: Investor Relations Department, by telephone at 314-727-2087, or by going to Viasystems’ Investor Info page on its corporate website at www.viasystems.com.

No Offer or Solicitation

The information in this communication is for informational purposes only and is neither an offer to purchase, nor a solicitation of an offer to sell, subscribe for or buy any securities or the solicitation of any vote in any jurisdiction pursuant to the proposed transactions or otherwise, nor shall there be any sale, issuance or transfer of securities in any jurisdiction in contravention of applicable law. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

Participants in the Solicitation

The Company and Viasystems and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from Viasystems’ stockholders in connection with the proposed Merger and may have direct or indirect interests in the proposed Merger. Information about the Company’s directors and executive officers is set forth in the Company’s Proxy Statement on Schedule 14A for its 2014 Annual Meeting of Stockholders, which was filed with the SEC on March 14, 2014, and its Annual Report on Form 10-K for the fiscal year ended December 30, 2013, which was filed with the SEC on February 21, 2014. These documents are available free of charge at the SEC’s website at www.sec.gov, and from the Company by contacting Investor Relations by mail at TTM Technologies, Inc., 1665 Scenic Avenue, Suite 250, Costa Mesa, CA 92626, Attn: Investor Relations Department, by telephone at 714-327-3000, or by going to the Company’s Investor Relations page on its corporate website at www.ttmtech.com. Information about Viasystems’ directors and executive officers is set forth in Viasystems’ Proxy Statement on Schedule 14A for its 2014 Annual Meeting of Stockholders, which was filed with the SEC on March 14, 2014, and its Annual Report on Form 10-K for the fiscal year ended December 31, 2013, which was filed with the SEC on February 14, 2014. These documents are available free of charge at the SEC’s website at www.sec.gov, and from Viasystems by contacting Investor Relations by mail at Viasystems Group, Inc., 101 South Hanley Road, Suite 1800, St. Louis, MO 63105, Attn: Investor Relations Department, by telephone at 314-727-2087, or by going to Viasystems’ Investor Info page on its corporate website at www.viasystems.com. Additional information regarding the interests of participants in the solicitation of proxies in connection with the proposed Merger is included in the Proxy Statement/Prospectus that the Company filed with the SEC.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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