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                                                                       EXHIBIT 5

                               QUARLES & BRADY LLP
                            411 East Wisconsin Avenue
                               Milwaukee, WI 53202

                                                              June 11, 2001



Plexus Corp.
55 Jewelers Park Drive
P.O. Box 156
Neenah, Wisconsin 54957-0156

         Re:      Qtron, Inc. Employee Stock Option Plan

Gentlemen and Ladies:

         We are providing this opinion in connection with the Registration
Statement of Plexus Corp. (the "Company") on Form S-8 (the "Registration
Statement") filed under the Securities Act of 1933, as amended (the "Act"), with
respect to the proposed sale by the Company of up to 5,596 shares of Common
Stock, par value $.01 per share, of the Company (the "Shares") upon the exercise
of options and stock appreciation rights granted under the Qtron, Inc. 1994
Stock Incentive Plan, as amended (the "Plan"), which has been assumed by the
Company in a recent acquisition.

         We have examined (i) the Registration Statement; (ii) the Company's
Restated Articles of Incorporation and Bylaws, as amended to date; (iii) the
Plan; (iv) corporate proceedings relating to the adoption of the Plan and the
issuance of the Shares; and (v) such other documents and records as we have
deemed necessary in order to render this opinion. In rendering this opinion, we
have relied as to certain factual matters on certificates of officers of the
Company and of state officials.

         Based upon the foregoing, it is our opinion that:

         1. The Company is a corporation validly existing under the laws of the
State of Wisconsin.

         2. The Shares, when issued and paid for as contemplated by the
Registration Statement and the Plan, will be validly issued, fully paid and
non-assessable by the Company subject to the personal liability which may be
imposed on shareholders by Section 180.0622(2)(b) of the Wisconsin Business
Corporation Law, as judicially interpreted, for debts owing to employees for
services performed, but not exceeding six months service in any one case.
Although Section 180.0622(2)(b) provides that such person liability of
shareholders shall be "to an amount equal to the par value of shares owned by
them respectively, and to the consideration for which their shares without par
value was issued,"



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the Wisconsin Supreme Court, by a split decision without a written opinion, has
affirmed a judgment holding shareholders of a corporation liable under the
substantially identical predecessor statute in effect prior to January 1, 1991
(Section 180.40(6)) for unpaid employee wages to an amount equal to the
consideration for which their par value shares were issued rather than the
shares' lower stated par value. Local 257 of Hotel and Restaurant Employees and
Bartenders International Union v. Wilson Street East Dinner Playhouse, Inc., 126
Wis. 2d 284, 375 N.W.2d 664 (1985) (affirming the 1983 decision of the Circuit
Court for Dane County, Wisconsin, in Case No. 82-CV-0023). The case was
subsequently overturned on other grounds.

         We consent to the filing of this opinion as an Exhibit to the
Registration Statement. In giving our consent, we do not admit that we are
"experts" within the meaning of Section 11 of the Act, or that we come within
the category of persons whose consent is required by Section 7 of the Act.

                                            Very truly yours,



                                            QUARLES & BRADY LLP