<PAGE>   1
                                                                    EXHIBIT 10.2

                   "AMENDMENT No. 1 TO EMPLOYMENT AGREEMENT"



     This Amendment Number One To Employment Agreement is made as of March 24,
1999 and is entered into in Concord, New Hampshire, by and between Aavid Thermal
Technologies, Inc., a Delaware corporation with its principal place at Concord,
New Hampshire (the "Company"), and John W. Mitchell of Gilford, New Hampshire
(the "Executive").

     WHEREAS, the Company and Executive entered into a certain Employment
Agreement as of December 5, 1995 (the "Employment Agreement").

     WHEREAS, the parties wish to amend the term and bonus provisions of the
Employment Agreement and to provide for changes of control of the Company.

     NOW, THEREFORE in consideration of the foregoing premises and the mutual
promises, terms, provisions and conditions set forth herein, the parties hereby
agree:

1.   DEFINED TERMS. Words or terms not otherwise defined herein, shall have the
meaning as set forth in the Employment Agreement.

2.   AMEND PARAGRAPH 2. Paragraph 2 shall be amended such that the automatic
renewal shall be extended from successive one (1) year terms to successive two
(2) year terms, and the notice period of a party's intent not to renew the
Employment Agreement is extended from ninety (90) days to one hundred and eighty
(180) days.

3.   AMEND PARAGRAPH 4(B). Paragraph 4(b) of the Employment Agreement is hereby
amended in its entirety to read as follows:

     (b)  INCENTIVE AND BONUS COMPENSATION. The Executive shall participate in
Incentive and Bonus Compensation Programs made available to executives of the
company generally, or any key management incentive plans, such that the annual
bonus target figure shall be the amount set annually by the Company's
Compensation Committee or Board of Directors.

4.   Add new Paragraphs 23 through 30 to the Employment Agreement which describe
Executive's "Change-In-Control" rights, as follows:

     23.  CHANGE-IN-CONTROL TERM. Notwithstanding any provision to the contrary
          herein, this Change-In-Control provision shall be effective as of the
          date of the date hereof and shall continue to be effective for the
          period ending on the "Expiration Date" which shall coincide with the
          end of the term of the Employment Agreement or any renewal thereof.

     24.  DEFINITION OF "CHANGE IN CONTROL". For the purposes of this Agreement,
          a "Change in Control" of the Company shall be deemed to have occurred
          upon:


          a)   An acquisition by any individual, entity or group (a "Person") of
               beneficial ownership of fifty percent (50%) or more of the then
               outstanding shares of common stock of the Company ("Common
               Stock").

          b)   A change in the composition of the Board such that the
               individuals who, as of the date hereof, constitute the Board (the
               Board as of the date hereof shall be hereinafter referred to as
               the "Incumbent Board") cease for any reason to constitute at
               least a majority of the Board; provided, that in making such
               determination directors who were elected by, or on the
               recommendation of, such present majority, shall be excluded;


                                      -1-
<PAGE>   2


          c)   The occurrence of a (i) merger, consolidation, reorganization or
               similar corporate transaction, in which the Company does not
               survive as an independent public company; (ii) the sale or other
               disposition of all or substantially all of the assets of the
               Company, or (iii) a complete liquidation or dissolution of the
               Company.


     25.  COVERED TERMINATION. The termination benefits described in Section 26
          hereof shall be provided to the Executive in the event that he suffers
          a "Covered Termination" of his employment with the Company during the
          "Protection Period" or, to the extent provided in such Section 26,
          shall be provided upon the earlier of a Change in Control or a Covered
          Termination. For purposes hereof, the "Protection Period" shall be the
          six month period that commences on the date of the Change in Control.
          For purposes hereof, "Covered Termination" shall mean (i) termination
          of employment by the Company other than for "Cause" as defined in this
          Employment Agreement or (ii) termination of employment by the
          Executive for "Good Reason" as described below. During the Protection
          Period, Company shall provide Executive with the same Base Salary,
          bonus opportunities, and benefits as he received prior to the
          Change-in-Control.

          a)   COMPENSATION DURING DISPUTE. If a dispute arises as to a
               purported termination for Cause, and the Executive institutes a
               proceeding for a determination as to rights under this Agreement,
               the Company shall continue to pay the Executive the full
               compensation in effect when the notice giving rise to the dispute
               was given (including, but not limited to, salary and bonuses) and
               continue the Executive as a participant in all compensation,
               benefit and insurance plans in which the Executive was
               participating when the notice giving rise to the dispute was
               given, until final judicial determination as to whether Cause or
               Good Reason existed. Amounts paid under this Section 25 are in
               addition to all other amounts due under this Agreement and shall
               not be offset against or reduce any other amounts due under this
               Agreement.

          b)   TERMINATION FOR GOOD REASON. For purposes of this Agreement, the
               Executive shall have "Good Reason" to terminate his employment
               with the Company (i) if by the end of the Protection Period the
               Company and Executive do not enter into a new or amended written
               employment agreement; or (ii) if the Company breaches the terms
               of this Employment Agreement as amended during the Protection
               Period. For the purpose of subparagraph (i) above, Executive
               shall have fifteen (15) days after the end of the Protection
               Period to notify Company of his termination for Good Reason.

     26.  CONSEQUENCES OF COVERED TERMINATION. In the event that the Executive's
          employment with the Company shall have been terminated during the
          Protection Period in a manner that shall constitute a Covered
          Termination, the Company shall provide the following severance
          payments and benefits to the Executive:

          a)   BASE SALARY. Within fifteen (15) days following the Covered
               Termination, the Company shall deliver to Executive a lump-sum
               cash payment equal to 2.0 times the Executive's Base Salary in
               effect at the time of the Covered Termination. For purposes of
               this Section 26, the Executive's Base Salary shall be determined
               immediately prior to the Change-in-Control.

          b)   WELFARE BENEFITS. The Executive shall be entitled to coverage and
               benefits, at the Company's sole expense, for a period of two
               years following his Covered Termination (the "Continuation
               Period"), under all welfare benefit plans of the Company. All
               such benefits shall apply to the Executive and any of his
               dependents who would have been eligible for coverage if the
               Executive had continued to be employed by the Company for the
               Continuation Period. At the expiration of the Continuation
               Period, the Executive shall be treated as a then terminating


                                      -2-
<PAGE>   3


               employee of the Company with respect to the right to elect
               continued medical and dental Coverages in accordance with section
               4980B of the Internal Revenue Code of 1986, as amended.

               c) OUTPLACEMENT. During the twelve-month period commencing on the
               date of Covered Termination, the Company shall provide to the
               Executive, at the Company's sole expense, executive outplacement
               services (commensurate with the Executive's position), office
               space and secretarial support services.

          27.  INSURANCE. The Company shall maintain in full force and effect
               for the benefit of the Executive, for the duration of all
               applicable statute of limitations periods, liability insurance
               policies at least as favorable to the Executive as those
               maintained by the Company for the benefit of its directors and
               officers at the time of the Change in Control, provided that such
               policies are provided to its directors and officers generally or
               are reasonably obtainable by the Company.

          28.  NO OBLIGATION TO MITIGATE. The Executive shall be under no
               obligation to minimize or mitigate damages by seeking other
               employment, and the obtaining of any such other employment shall
               in no event effect any reduction of the Company's obligation to
               make the payments and provide the benefit Coverages required
               under this Agreement.

          29.  SUCCESSORS AND ASSIGNS. This Agreement and all rights hereunder
               are personal to the Executive and shall not be assignable;
               provided, however, all of the Executive's rights to compensation
               following his death shall inure to the benefit of his surviving
               spouse, personal representatives or designees or other legal
               representatives, as the case may be. The Company and any
               successor to its business and/or assets shall remain liable to
               Executive hereunder.

          30.  LEGAL EXPENSES. The Company shall pay directly or reimburse the
               Executive (at the Executive's option) for any and all legal fees
               and expenses incurred by the Executive relating to the
               enforcement or the attempted enforcement, of any obligation of
               the Company hereunder, regardless of outcome, provided that the
               Executive's claims in such regard are not determined by a trier
               of fact to be frivolous.

     5.   CONTINUATION OF EMPLOYMENT AGREEMENT. Except as specifically amended
     herein, the Employment Agreement remains in full force and effect and the
     parties agree to be bound thereby. To the extent there is any conflict
     between the terms of Sections 26 through 30 herein and the remainder of the
     Agreement, the terms of Sections 26 through 30 shall govern.

     6.   CHANGE OF PARTY. Aavid Engineering, Inc. shall no longer be a party to
     the Employment Agreement.


                                      -3-

<PAGE>   4


     This Agreement is executed as of the date set forth in the opening
paragraph.

     IN WITNESS WHEREOF, the parties have executed these presents as of the day
and year first above written.


AAVID THERMAL TECHNOLOGIES, INC.
and AAVID THERMAL PRODUCTS, INC.
(Formerly AAVID ENGINEERING, INC.)        EXECUTIVE



By       s/s Ronald F. Borelli                  s/s John W. Mitchell
  ----------------------------------      --------------------------------------

Name     Ronald F. Borelli                Name  John W. Mitchell
    --------------------------------          ----------------------------------

Title    Chief Executive Officer          Title Vice President & General Counsel
     -------------------------------           ---------------------------------




                                      -4-