Exhibit 10.46 FIRST AMENDMENT TO CREDIT AGREEMENT AGREEMENT AND AMENDMENT made as of the 16th day of December, 1999, by and between USTrust ("Lender") and BTU International, Inc. ("Borrower"). WHEREAS, Lender and Borrower are parties to a Credit...

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                                                                   Exhibit 10.46

                       FIRST AMENDMENT TO CREDIT AGREEMENT

     AGREEMENT AND AMENDMENT made as of the 16th day of December, 1999, by and
between USTrust ("Lender") and BTU International, Inc. ("Borrower").

     WHEREAS, Lender and Borrower are parties to a Credit Agreement dated
September 5, 1997 (the "Credit Agreement") and certain other Loan Documents (as
defined in the Credit Agreement) under which Lender has made loans and extended
credit, form time to time, to Borrower;

     WHEREAS, the Borrowers have requested that Lender agree to amend the Credit
Agreement to, among other things, extend the Termination Date under the Credit
Agreement and modify the Debt Service Coverage Ratio;

     WHEREAS, Lender is prepared to agree to the foregoing amendments but only
on the terms and subject to the conditions set forth herein,

     NOW, THEREFORE, based on these premises, and in consideration of the mutual
promises herein contained, and other good and valuable consideration the receipt
and sufficiency of which are hereby acknowledged, Lender and Borrowers hereby
agree:

SECTION 1.  DEFINITIONS.

     Capitalized terms not defined herein shall have the meanings ascribed to
them in the Credit Agreement.

SECTION 2. AMENDMENTS TO CREDIT AGREEMENT. Borrower and Lender agree that the
Credit Agreement is amended as follows:

     2.1       Section 5.5(d) of the Credit Agreement is deleted and replaced
          with the following:

          "(d) Debt Service Coverage Ratio. Allow the ratio of (i) EBITDA of
          Borrower minus unfinanced Capital Expenditures minus cash income taxes
          paid that apply to the current year's Earnings minus Dividends and
          Distributions, to (ii) Borrower's interest expense plus Current
          Maturities of Long Term Debt, calculated retrospectively for the
          period of the immediately preceding four fiscal quarters, to be less
          than 1.20 to 1.00 on the last day of any fiscal quarter, provided that
          for purposes of determining the Debt Service Coverage Ratio,
          unfinanced Capital Expenditures shall not be deducted from the
          numerator of the ratio, so long as any Loans or Letters of Credit
          outstanding under this Agreement do not exceed $2,000,000 in the
          aggregate."

     2.2       Schedule I of the Credit Agreement is amended to delete the
          definition of "Termination Date" and to replace it with the following:

          "Termination Date" - the earlier of (a) April 30, 2004, and (b) the
          date the Lender's Commitment to make Loans is terminated pursuant to
          Section 7.2 of Article 7."

SECTION 3.  ACKNOWLEDGMENT OF OBLIGATIONS AND COLLATERAL.

     3.1  Borrower hereby acknowledges and agrees that it is unconditionally
          liable to Lender for the prompt and punctual performance of all
          Obligations under the Credit Agreement and other


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          Loan Documents, and that Borrower has no defenses, counterclaims or
          offsets with respect to the full payment and performance of all
          Obligations.

     3.2  Borrower hereby acknowledge and agree that Lender has and shall
          continue to have valid and enforceable and duly perfected security
          interests in and to all Collateral to secure the Obligations.

SECTION 4.  REPRESENTATIONS AND WARRANTIES.

     Borrower represents and warrants that each of the warranties and
representations contained in the Credit Agreement and each other Loan Document
is accurate and complete as of the date hereof.

SECTION 5.  CONTINUING EFFECT OF CREDIT AGREEMENT.

     Except as expressly set forth herein, or in any other documents to be
executed and delivered in connection herewith, the Loan Documents shall remain
in full force and effect in accordance with their terms.

SECTION 6.  MISCELLANEOUS.

     This Amendment, together with the Loan Documents, contains the entire
agreement of the parties with respect to the subject matter and supersedes all
prior negotiations, offers and discussions relating thereto. This Amendment may
be amended, modified, waived, discharges or terminated only by a writing signed
by the party to be charged with such amendment, modification, discharge or
termination. This Amendment shall be governed by Massachusetts law. This
Amendment may be executed by one or more of the parties in separate
counterparts, and all of such counterparts taken together shall be deemed to
constitute one and the same instrument.

     Executed under seal as of date set forth above.

                                           BTU INTERNATIONAL, INC.

                                           By:  X. Xxxxx
                                                --------
                                            Name:  X. Xxxxx
                                            Title  Vice President

                                           USTRUST

                                           By:  Xxxx X. Xxxxxx
                                                --------------
                                            Name:  Xxxx X. Xxxxxx
                                            Title  Vice President