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                                                                     EXHIBIT 4.1

                   FIRST AMENDMENT TO STOCK PURCHASE AGREEMENT


         This First Amendment to Stock Purchase Agreement (the "First
Amendment"), dated as of December 28, 2000, among Sheldahl, Inc., a Minnesota
corporation (the "Company"), and the individuals and entities listed on Exhibit
A hereto (the "Purchasers"), amends the Stock Purchase Agreement, dated as of
November 10, 2000 (the "Purchase Agreement"), among the Company and the
Purchasers. Capitalized terms not defined herein shall have the meanings set
forth in the Purchase Agreement.

         WHEREAS, the Company and the Purchasers entered into the Purchase
Agreement effective November 10, 2000 to effect the sale by the Company to the
Purchasers of (i) shares of the Company's Series G Convertible Preferred Stock,
par value $1.00 per share (the "Series G Preferred"), and (ii) shares of the
Company's Common Stock, par value $.25 per share (the "Common Stock") pursuant
to the terms contained therein; and

         WHEREAS, subsequent to the execution and delivery of the Purchase
Agreement, certain developments occurred as a result of which the Company and
the Purchasers determined that certain amendments to the Purchase Agreement, and
the Disclosure Letter and Exhibits attached thereto, would be appropriate.

         NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows.

1. Amendment of the Purchase Agreement. The Purchase Agreement is hereby amended
as follows:

         (a) Section 1.1(c) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(c) Subject to the terms and conditions set forth herein, at
                  the Closing (as defined below), the Company shall issue and
                  sell to the Purchasers and the Purchasers, severally and not
                  jointly, shall purchase 9,783,571 shares of Common Stock (the
                  "Common Shares")."

         (b) Section 1.2(b) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(b) The purchase price per Common Share shall be $1.40."

         (c) Section 1.3(c) of the Purchase Agreement shall be amended by
deleting the first sentence of such Section in its entirety, and the following
shall be substituted therefor:

                  "The Closing of the purchase and sale of the Shares (the
                  "Closing") shall take place at the offices of Lindquist &
                  Vennum P.L.L.P., 4200 IDS Center, 80 South 8th Street,
                  Minneapolis, Minnesota simultaneous with the closing of the
                  transactions contemplated by the Agreement and Plan of Merger
                  dated as of November 10, 2000, as amended, modified or
                  supplemented from time to time, among the Company, IFT West
                  Acquisition Company, International Flex Holdings, Inc. ("IFH")
                  and its stockholders (the "Merger Agreement")."


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         (d) Section 2.1(c) of the Purchase Agreement shall be amended by
deleting the first three sentences of such Section in their entirety, and the
following shall be substituted therefor:

                  "The authorized, issued and outstanding capital stock of the
                  Company as of November 1, 2000 is set forth in Part 2.1(c) of
                  the Disclosure Letter. Except as specifically disclosed in
                  Part 2.1(c) of the Disclosure Letter, no shares of the capital
                  stock or other securities of the Company are entitled to
                  preemptive or similar rights, nor is any holder of shares of
                  the capital stock or other securities of the Company entitled
                  to preemptive or similar rights. Except as disclosed in Part
                  2.1(c) of the Disclosure Letter, as of November 1, 2000, there
                  are no outstanding options, warrants or commitments of any
                  character whatsoever relating to, or, except as a result of
                  the purchase and sale of the Shares hereunder, securities,
                  rights or obligations convertible into or exchangeable for, or
                  giving any person any right to subscribe for or acquire any
                  shares of Common Stock of the Company, or contracts,
                  commitments, understandings, or arrangements by which the
                  Company is bound to issue additional shares of the Company's
                  Common Stock, or securities or rights convertible or
                  exchangeable into shares of the Company's Common Stock, or any
                  shares of the Company's Common Stock reserved for issuance."

         (e) Section 2.1(d) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(d) Issuance of Shares. The Series G Preferred Shares are
                  duly authorized and, when issued in accordance with the terms
                  hereof and the Certificate of Designation, shall be validly
                  issued, fully paid and non-assessable. The Common Shares are
                  duly authorized and, when issued in accordance with the terms
                  hereof, shall be validly issued, fully paid and
                  non-assessable. Except as set forth in Part 2.1(d) of the
                  Disclosure Letter, as of the Closing Date, the Company will
                  have and, at all times while any Series G Preferred Shares are
                  outstanding will maintain, an adequate reserve of duly
                  authorized shares of its Common Stock to enable it to perform
                  its obligations under this Agreement and the Certificate of
                  Designation with respect to the number of Series G Preferred
                  Shares issued and outstanding at the Closing Date. The shares
                  of Common Stock issuable upon conversion of the Series G
                  Preferred Shares and which may be issued as payment of
                  dividends on the Series G Preferred Shares are collectively
                  referred to herein as the `Underlying Shares.' When issued in
                  accordance with the terms hereof and the Certificate of
                  Designation, assuming the availability of sufficient
                  authorized shares of Common Stock of the Company at such time
                  of issuance, the Underlying Shares will be duly authorized,
                  validly issued, fully paid and non-assessable, free and clear
                  of all liens, claims, encumbrances or defects of any kind
                  (collectively, "Liens"), except as set forth in any required
                  legends thereon, including those required under the Governance
                  Agreement."

         (f) Section 2.1(k) of the Purchase Agreement shall be amended by
deleting the last sentence of such Section in its entirety, and the following
shall be substituted therefor:


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                  "Except as set forth in Part 2.1(k) of the Disclosure Letter,
                  the Company is, and has no reason to believe that it will not
                  in the foreseeable future continue to be, in compliance with
                  all such listing and maintenance requirements."

         (g) Section 2.2(h) of the Purchase Agreement shall be amended by
deleting the first sentence of such Section in its entirety, and the following
shall be substituted therefor:

                  "No Purchaser is an `Affiliate' or `Associate' (as such terms
                  are defined in Rule 12b-2 under the Exchange Act) of any other
                  Purchaser or is acting in concert with any other Purchaser,
                  except (i) that Ampersand IV Limited Partnership and Ampersand
                  IV Companion Fund Limited Partnership may be deemed to be
                  Affiliates or Associates of one another, (ii) to the extent
                  that a member or partner of a Purchaser or a member of a
                  partner of a Purchaser is a member or partner of another
                  Purchaser or a member or partner of a member or partner of
                  another Purchaser, (iii) by virtue of the existence of the
                  Governance Agreement and/or the Voting Agreement dated as of
                  November 10, 2000, as amended, supplemented or modified from
                  time to time, among Ampersand IV Limited Partnership,
                  Ampersand IV Companion Fund Limited Partnership, Morgenthaler
                  and Sound Beach Technology Partners, LLC relating to voting of
                  the shares of Common Stock in an election of directors to the
                  Company's board of directors (the "Voting Agreement"), and
                  (iv) as otherwise provided in any Transaction Document."

         (h) Section 2.2(l) of the Purchase Agreement shall be amended by
deleting the first sentence of such Section in its entirety, and the following
shall be substituted therefor:

                  "At and after the Closing, except for (i) the shares of Common
                  Stock acquired pursuant to this Agreement, (ii) the shares of
                  Common Stock acquired upon conversion of the Series G
                  Preferred Shares and as dividends on the Series G Preferred
                  Shares, (iii) the shares of Common Stock acquired pursuant to
                  the Merger Agreement, and/or (iv) the shares of Common Stock
                  acquired upon exercise of the Warrants purchased under the
                  Subordinated Notes Purchase Agreement, and except by virtue of
                  the existence of the Governance Agreement and/or the Voting
                  Agreement, no Purchaser shall be a Beneficial Owner of fifteen
                  percent (15%) or more of outstanding shares of the Company's
                  Common Stock."

         (i) Section 3.7 of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "3.7 Amendment to Articles of Incorporation. The Company shall
                  use its reasonable best efforts to cause its stockholders to
                  amend the Company's Amended and Restated Articles of
                  Incorporation as soon as reasonably practical after the
                  Closing Date to increase the number of authorized shares of
                  the Company's Common Stock so that an adequate reserve of duly
                  authorized shares of Common Stock may be reserved in order to
                  enable the Company to perform its obligations under this
                  Agreement and the Certificate of Designation with respect to
                  the number of Series G Preferred Shares issued and outstanding
                  at the Closing Date."


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         (j) Section 4.1(i) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(i) Registration Rights Agreement. Such Purchaser shall have
                  received an executed Registration Rights Agreement, dated as
                  of December 28, 2000, in the form of Exhibit D (the
                  "Registration Rights Agreement") from the Company."

         (k) Section 4.1(j) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(j) Governance Agreement. Such Purchaser shall have received
                  an executed Governance Agreement, dated as of December 28,
                  2000, in the form of Exhibit E (the "Governance Agreement")
                  from the Company."

         (l) Section 4.1(k) of the Purchase Agreement shall be deleted in its
entirety, and the following shall be substituted therefor:

                  "(k) Subordinated Notes Purchase Agreement. All of the
                  conditions to the obligations of the purchasers under the
                  Subordinated Notes and Warrant Purchase Agreement among the
                  Company and the purchasers listed on Schedule I thereto dated
                  as of November 10, 2000, as amended, modified or supplemented
                  from time to time (the "Subordinated Notes Purchase
                  Agreement"), other than the conditions related to this
                  Agreement, shall have been satisfied or waived by the parties
                  thereto at or before the Closing."

         (m) Section 6.1 of the Purchase Agreement shall be amended by adding
the following sentence immediately at the end of such Section:

                  "Without limiting any of the forgoing, the Company shall
                  reimburse the Purchasers for all fees associated with any
                  filings under the HSR Act made by any of the Purchasers prior
                  to, on or following the Closing."

         (n) Exhibit A of the Purchase Agreement shall be deleted in its
entirety, and shall be replaced for all purposes with the new Exhibit A attached
hereto.

         (o) Exhibit B of the Purchase Agreement shall be deleted in its
entirety, and shall be replaced for all purposes with the new Exhibit B attached
hereto.

         (p) Exhibit C of the Purchase Agreement shall be deleted in its
entirety, and shall be replaced for all purposes with the new Exhibit C attached
hereto.

         (q) Exhibit D of the Purchase Agreement shall be deleted in its
entirety, and shall be replaced for all purposes with the new Exhibit D attached
hereto.

         (r) Exhibit E of the Purchase Agreement shall be deleted in its
entirety, and shall be replaced for all purposes with the new Exhibit E attached
hereto.


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         (s) The Disclosure Letter shall be deleted in its entirety, and shall
be replaced for all purposes with the new Disclosure Letter attached hereto as
Addendum 1, provided that the Disclosure Letter delivered upon execution of the
Purchase Agreement on November 10, 2000 shall continue to apply with respect to
the representations and warranties of the Company made in the Purchase Agreement
as of November 10, 2000.

2. Representations and Warranties. The Company hereby confirms that the
representations and warranties of the Company contained in Section 2.1 of the
Purchase Agreement, subject to those matters set forth in the updated Disclosure
Letter attached hereto as Addendum 1, are true and correct on and as of the date
hereof as if made on and as of the date hereof (except to the extent that such
representations and warranties expressly relate to an earlier date). Each
Purchaser hereby confirms that the representations and warranties of the
Purchasers contained in Section 2.2 of the Purchase Agreement are true and
correct on and as of the date hereof as if made on and as of the date hereof
(except to the extent that such representations and warranties expressly relate
to an earlier date). The Company and the Merger Sub hereby confirms that the
representations and warranties of the Company and the Merger Sub set forth in
Article IV of the Merger Agreement and incorporated in the Purchase Agreement by
reference pursuant to Section 2.3 thereto, subject to the updated Parent
Disclosure Letter attached as exhibit A to the First Amendment to the Merger
Agreement, are true and correct on and as of the date hereof as if made on and
as of the date hereof (except to the extent that such representations and
warranties expressly relate to an earlier date). IFH hereby confirms that the
representations and warranties of IFH set forth in Article II of the Merger
Agreement and incorporated in the Purchase Agreement by reference pursuant to
Section 2.3 thereto, subject to the updated Company Disclosure Letter attached
as exhibit B to the First Amendment to the Merger Agreement, are true and
correct on and as of the date hereof as if made on and as of the date hereof
(except to the extent that such representations and warranties expressly relate
to an earlier date). The IFH Stockholders hereby confirm that the
representations and warranties of the IFH Stockholders set forth in Article III
of the Merger Agreement and incorporated in the Purchase Agreement by reference
pursuant to Section 2.3 thereto are true and correct on and as of the date
hereof as if made on and as of the date hereof (except to the extent that such
representations and warranties expressly relate to an earlier date).

3. Miscellaneous.

         (a) Effect of Amendment. Except as otherwise expressly set forth in
this First Amendment, nothing herein shall be deemed to constitute an amendment,
modification or waiver of any of the terms and conditions of the Purchase
Agreement or the Exhibits thereto, all of which terms and conditions shall
remain in full force and effect as originally constituted and the undersigned
shall remain obligated pursuant to the terms thereunder.

         (b) Governing Law. This First Amendment shall be governed by and
construed and enforced in accordance with the internal laws of the State of
Minnesota without regard to the principles of conflicts of law thereof.

         (c) Execution. This First Amendment may be executed in two or more
counterparts, all of which when taken together shall be considered one and the
same agreement. In the event that any signature is delivered by facsimile
transmission, such signature shall create a valid and


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binding obligation of the party executing (or on whose behalf such signature is
executed) the same with the same force and effect as if such facsimile signature
page were an original thereof.



                  [Remainder of page intentionally left blank]


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         IN WITNESS WHEREOF, The Company and the Purchasers have each caused
this First Amendment to the Stock Purchase Agreement to be duly executed as of
the date first written above.


                                    COMPANY:

                                    SHELDAHL, INC.

                                    By: /s/ Edward L. Lundstrom
                                       -----------------------------------------
                                       Name: Edward L. Lundstrom
                                       Title: President


                                    PURCHASERS:

                                    MORGENTHALER VENTURE PARTNERS V, L.P.


                                    By: /s/ John D. Lutsi
                                       -----------------------------------------
                                       Name: John D. Lutsi,
                                       its General Partner


                                    AMPERSAND IV LIMITED PARTNERSHIP

                                    BY:  AMP-IV MANAGEMENT COMPANY
                                         LIMITED LIABILITY COMPANY,
                                         ITS GENERAL PARTNER

                                    By: /s/ Richard A. Charpie
                                       -----------------------------------------
                                       Name: Richard A. Charpie
                                       Title: Principal Managing Member


                                    AMPERSAND IV COMPANION FUND
                                    LIMITED PARTNERSHIP

                                    BY:  AMP-IV MANAGEMENT COMPANY
                                         LIMITED LIABILITY COMPANY,
                                         ITS GENERAL PARTNER

                                    By: /s/ Richard A. Charpie
                                       -----------------------------------------
                                       Name: Richard A. Charpie
                                       Title: Principal Managing Member


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                                 LIMITED JOINDER

         IFH, the Merger Sub and the IFH Stockholders hereby join in the
foregoing First Amendment to Stock Purchase Agreement for the limited purposes
of confirming the representations and warranties set forth in Section 2.3 of the
Purchase Agreement, as amended hereby, on the date hereof as if they were
parties hereto and as if such representations and warranties were made as of the
date hereof (except to the extent that such representations and warranties
expressly relate to an earlier date).

                                    INTERNATIONAL FLEX HOLDINGS, INC.

                                    By: /s/ John D. Lutsi
                                       -----------------------------------------
                                       Name: John D. Lutsi
                                       Title: President


                                    IFT WEST ACQUISITION COMPANY

                                    By: /s/ Edward L. Lundstrom
                                       -----------------------------------------
                                       Name: Edward L. Lundstrom
                                       Title: President


                                    IFH STOCKHOLDERS:

                                    MORGENTHALER VENTURE PARTNERS V, L.P.


                                    By: /s/ John D. Lutsi
                                       -----------------------------------------
                                       Name: John D. Lutsi,
                                       its General Partner


                                    SOUND BEACH TECHNOLOGY PARTNERS, LLC


                                    By: /s/ Donald R. Friedman
                                       -----------------------------------------
                                       Name: Donald R. Friedman
                                       Title: President and Chief Executive
                                              Officer


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                                                                       EXHIBIT A

                             SCHEDULE OF PURCHASERS

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------------------------------------------------------
                                                                     # OF
                                                                   SERIES G                         BENEFICIAL
                  PURCHASER                        AGGREGATE       PREFERRED      # OF COMMON        OWNERSHIP       STATE OF
                NAME & ADDRESS                  PURCHASE PRICE      SHARES           SHARES         PERCENTAGE      RESIDENCE
--------------------------------------------------------------------------------------------------------------------------------
<S>                                               <C>                <C>           <C>                 <C>              <C>
Ampersand IV Limited Partnership                  $7,350,000         3,323         2,876,300           29.4%            MA
55 William Street
Suite 240
Wellesley, MA  02481-4003
--------------------------------------------------------------------------------------------------------------------------------
Ampersand IV Companion Fund                         $150,000            68            58,700            0.6%            MA
Limited Partnership
55 William Street
Suite 240
Wellesley, MA  02481-4003
--------------------------------------------------------------------------------------------------------------------------------
Morgenthaler Venture Partners V, L.P.            $17,500,000         7,912         6,848,571           70.0%            OH
Terminal Tower
50 Public Square, Suite 2700
Cleveland, OH  44113
--------------------------------------------------------------------------------------------------------------------------------
TOTAL                                            $25,000,000        11,303         9,783,571          100.0%
--------------------------------------------------------------------------------------------------------------------------------
</TABLE>



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