<PAGE>

                                                                  EXHIBIT 10.1.8


                               SECOND AMENDMENT

          SECOND AMENDMENT, dated as of December 28, 2000 (this "Amendment"), to
                                                                 ---------
the Amended and Restated Credit and Guarantee Agreement, dated as of July 27,
2000, (as amended by the First Amendment, dated as of November 17, 2000, and as
may be further amended, supplemented or otherwise modified from time to time,
the "Credit Agreement"), among SMTC Corporation ("Holdings"), HTM Holdings, Inc.
     ----------------                             --------
(the "U.S. Borrower"), SMTC Manufacturing Corporation of Canada (the "Canadian
      -------------                                                   --------
Borrower"; together with the U.S. Borrower, the "Borrowers"), the several banks
--------                                         ---------
and other financial institutions or entities from time to time parties thereto
(the "Lenders"), Lehman Brothers Inc., as advisor, lead arranger and book
      -------
manager (in such capacity, the "Arranger"), The Bank of Nova Scotia, as
                                --------
syndication agent (in such capacity, the "Syndication Agent"), Lehman Commercial
                                          -----------------
Paper Inc., as general administrative agent (in such capacity, the "General
                                                                    -------
Administrative Agent"), The Bank of Nova Scotia, as Canadian administrative
--------------------
agent (in such capacity, the "Canadian Administrative Agent"), Lehman Commercial
                              -----------------------------
Paper Inc., as collateral monitoring agent (in such capacity, the "Collateral
                                                                   ----------
Monitoring Agent"), and General Electric Capital Corporation, as documentation
----------------
agent (in such capacity, the "Documentation Agent").
                              -------------------


                              W I T N E S S E T H
                              - - - - - - - - - -

          WHEREAS, Holdings and the Borrowers have requested that the Lenders
amend certain of the provisions of the Credit Agreement upon the terms and
subject to the conditions set forth below; and

          WHEREAS, the Required Lenders have agreed to amend the Credit
Agreement in the manner and upon the terms and subject to the conditions set
forth below;

          NOW, THEREFORE, the parties hereto hereby agree as follows:

          1.   Defined Terms. As used herein, terms defined in this Amendment or
               -------------
in the Credit Agreement are used herein as so defined.

          2.   Amendment to Section 11.5 of the Credit Agreement. Section 11.5
               -------------------------------------------------
of the Credit Agreement is hereby amended by (a) deleting the word "and" at the
end of paragraph (l); (b) deleting the period at the end of paragraph (m); (c)
inserting "; and" and (d) inserting the following new paragraph (n) at the end
of such Section:

          "(n) the sale by the U.S. Borrower and/or any of its Subsidiaries to
the Canadian Borrower of Accounts owing to any of them by third parties in an
aggregate amount not to exceed U.S. $12,800,000, in consideration for the
assignment of Indebtedness owing by
<PAGE>

                                                                               2

Holdings or the U.S. Borrower to the Canadian Borrower in an amount equal to the
fair value of the transferred Accounts."

          3.   Amendment to Section 11.6 of the Credit Agreement. Section 11.6
               -------------------------------------------------
of the Credit Agreement is hereby amended by (a) deleting the word "and" at the
end of paragraph (f); (b) deleting the period at the end of paragraph (g); (c)
inserting "; and" and (d) inserting the following new paragraph (h) at the end
of such Section:

          "(h) the Canadian Borrower may make Restricted Payments to SMTC Nova
Scotia Company and SMTC Nova Scotia may make Restricted Payments to Holdings in
the form of receivables owing to the Canadian Borrower from Holdings or the U.S.
Borrower in an aggregate amount not to exceed the paid-up capital of SMTC Nova
Scotia Company (estimated to be U.S. $19,415,000)."

          4.   Effectiveness. The Amendment shall become effective on the date
               -------------
(the "Second Amendment Effective Date") of satisfaction of the following
      -------------------------------
conditions precedent:

          (a)  The General Administrative Agent shall have received counterparts
     of this Amendment, duly executed and delivered by Holdings and each of the
     Borrowers.

          (b)  The General Administrative Agent shall have received executed
     Lender Consent Letters, substantially in the form of Exhibit A hereto
     ("Lender Consent Letters"), from Lenders constituting the Required Lenders
       ----------------------
     and the Required Prepayment Lenders.

          (c)  The General Administrative Agent shall have received an executed
     Acknowledgment and Consent, in the form set forth at the end of this
     Amendment, from each Loan Party other than Holdings and the Borrowers.

          (d)  All corporate and other proceedings, and all documents,
     instruments and other legal matters in connection with the transactions
     contemplated by this Amendment shall be satisfactory in form and substance
     to the General Administrative Agent.

          5.   Representations and Warranties. After giving effect to the
               ------------------------------
amendment contained herein, on the Second Amendment Effective Date, Holdings and
each of the Borrowers hereby confirms, reaffirms and restates the
representations and warranties set forth in Section 8 of the Credit Agreement;
provided that each reference in such Section 8 to "this Agreement" shall be
--------
deemed to be a reference both to this Amendment and to the Credit Agreement as
amended by this Amendment.

          6.   Continuing Effect; No Other Amendments. Except as expressly
               --------------------------------------
amended or waived hereby, all of the terms and provisions of the Credit
Agreement and the other Loan Documents are and shall remain in full force and
effect. The amendments contained herein shall not constitute an amendment or
waiver of any other provision of the Credit Agreement or the other Loan
Documents or for any purpose except as expressly set forth herein.
<PAGE>

                                                                               3

          7.   No Default. No Default or Event of Default shall have occurred
               ----------
and be continuing as of the Second Amendment Effective Date after giving effect
to this Amendment.

          8.   Counterparts. This Amendment may be executed in any number of
               ------------
counterparts by the parties hereto, each of which counterparts when so executed
shall be an original, but all the counterparts shall together constitute one and
the same instrument.

          9.   GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED
               -------------
AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.
<PAGE>

                                                                               4

          IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed and delivered by their respective proper and duly authorized officers
as of the day and year first above written.

                                     SMTC CORPORATION


                                     By:   /s/ Richard Smith
                                        ------------------------------
                                        Name:  Richard Smith
                                        Title: Chief Financial Officer


                                     HTM HOLDINGS, INC.


                                     By:   /s/ Richard Smith
                                        ------------------------------
                                        Name:  Richard Smith
                                        Title: Chief Financial Officer


                                     SMTC MANUFACTURING CORPORATION OF
                                     CANADA


                                     By:   /s/ Richard Smith
                                        ------------------------------
                                        Name:  Richard Smith
                                        Title: Chief Financial Officer


                                     LEHMAN COMMERCIAL PAPER INC., as
                                       General Administrative Agent


                                     By:   /s/ G. Andrew Keith
                                        ------------------------------
                                        Name:  G. Andrew Keith
                                        Title: Authorized Signatory


                                     LEHMAN COMMERCIAL PAPER INC., as
                                     Collateral Monitoring Agent and as a Lender


                                     By:   /s/ G. Andrew Keith
                                        ------------------------------
                                        Name:  G. Andrew Keith
                                        Title: Authorized Signatory
<PAGE>

                                                                               5

                                     THE BANK OF NOVA SCOTIA, as Canadian
                                     Administrative Agent


                                     By:   /s/ Paul Phillips
                                        ------------------------------
                                        Name:  Paul Phillips
                                        Title: Director


                                     THE BANK OF NOVA SCOTIA, as Syndication
                                     Agent and as a Lender


                                     By:   /s/ Jon Burckin
                                        ------------------------------
                                        Name:  Jon Burckin
                                        Title: Managing Director


                                     GENERAL ELECTRIC CAPITAL
                                     CORPORATION, as Documentation Agent and as
                                     a Lender


                                     By:
                                        ------------------------------
                                        Name:
                                        Title:
<PAGE>

                          ACKNOWLEDGMENT AND CONSENT

          Each of the undersigned parties to the Amended and Restated Guarantee
and Collateral Agreement, dated as of July 27, 2000, as amended by the First
Amendment, dated as of November 17, 2000 and as amended, supplemented or
otherwise modified from time to time, made by the undersigned in favor of Lehman
Commercial Paper Inc., as General Administrative Agent, for the benefit of the
Lenders, hereby (a) consents to the transactions contemplated by the foregoing
Amendment to the Amended and Restated Credit and Guarantee Agreement and (b)
acknowledges and agrees that the guarantees and grants of security interests
contained in such Amended and Restated Guarantee and Collateral Agreement and in
the Security Documents are, and shall remain, in full force and effect after
giving effect to this Amendment and all prior modifications to the Amended and
Restated Credit and Guarantee Agreement.

                                      SMTC CORPORATION


                                      By: /s/ Richard Smith
                                         ---------------------------
                                      Title: Chief Financial Officer


                                      HTM HOLDINGS, INC.


                                      By: /s/ Richard Smith
                                         ---------------------------
                                      Title: Chief Financial Officer


                                      SMTC MANUFACTURING CORPORATION
                                      OF TEXAS


                                      By: /s/ Richard Smith
                                         ---------------------------
                                      Title: Chief Financial Officer


                                      SMTC MANUFACTURING CORPORATION
                                       OF CALIFORNIA


                                      By: /s/ Richard Smith
                                         ---------------------------
                                      Title: Chief Financial Officer

<PAGE>

                                       SMTC MANUFACTURING CORPORATION
                                       OF NORTH CAROLINA


                                       By: /s/ Richard Smith
                                          ---------------------------
                                       Title: Chief Financial Officer


                                       SMTC MEX HOLDINGS, INC.


                                       By: /s/ Richard Smith
                                          ---------------------------
                                       Title: Chief Financial Officer


                                       SMTC MANUFACTURING CORPORATION
                                       OF COLORADO


                                       By: /s/ Richard Smith
                                          ---------------------------
                                       Title: Chief Financial Officer


                                       SMTC MANUFACTURING CORPORATION
                                       OF MASSACHUSETTS


                                       By: /s/ Richard Smith
                                          ---------------------------
                                       Title: Chief Financial Officer


                                       PENSAR CORPORATION


                                       By: /s/ Richard Smith
                                          ---------------------------
                                       Title: Chief Financial Officer
<PAGE>

                                                                       EXHIBIT A
                             LENDER CONSENT LETTER

                              HTM HOLDINGS, INC.
                   SMTC MANUFACTURING CORPORATION OF CANADA
                             AMENDED AND RESTATED
                        CREDIT AND GUARANTEE AGREEMENT
                           DATED AS OF JULY 27, 2000

To:  Lehman Commercial Paper Inc.,
      as General Administrative Agent
     3 World Financial Center
     New York, New York 10285

Ladies and Gentlemen:

          Reference is made to the Amended and Restated Credit and Guarantee
Agreement, dated as of July 27, 2000, as amended by the First Amendment, dated
as of November 17, 2000 and as may be further amended, supplemented or otherwise
modified from time to time (the "Credit Agreement"), among HTM Holdings, Inc.
                                 ----------------
(the "U.S. Borrower"), SMTC Corporation ("Holdings"), SMTC Manufacturing
      -------------                       --------
Corporation of Canada (the "Canadian Borrower"; together with the U.S. Borrower,
                            -----------------
the "Borrowers"), the several banks and other financial institutions or entities
     ---------
from time to time parties thereto (the "Lenders"), Lehman Commercial Paper Inc.,
                                        -------
as general administrative agent (in such capacity, the "General Administrative
                                                        ----------------------
Agent"), and others.  Unless otherwise defined herein, capitalized terms used
-----
herein and defined in the Credit Agreement are used herein as therein defined.

          The Borrowers have requested that the Lenders consent to amend the
Credit Agreement on the terms described in the Second Amendment to which a form
of this Lender Consent Letter is attached as Exhibit A (the "Second Amendment").
                                                             ----------------

          Pursuant to Section 15.1 of the Credit Agreement, the undersigned
Lender hereby consents to the execution by the General Administrative Agent of
the Second Amendment.

                                Very truly yours,

                                AMMC, CDO I, LIMITED (American Money Management
                                 Corp. as Collateral Manager)
                                -----------------------------------------------
                                (NAME OF LENDER)

                                By:   /s/ David P. Meyer
                                   --------------------------------------------
                                   Name:  David P. Meyer
                                   Title: Vice President


                                AMMC, CDO II, LIMITED (American Money Management
                                 Corp. as Collateral Manager)
                                -----------------------------------------------
                                (NAME OF LENDER)

                                 By:   /s/ David P. Meyer
                                    --------------------------------------------
                                    Name:  David P. Meyer
                                    Title: Vice President


                                COMERICA BANK
                                -----------------------------------------------
                                (NAME OF LENDER)

                                 By:   /s/ Monica Lewis
                                    --------------------------------------------
                                    Name:  Monica Lewis
                                    Title: International Lending Officer


                                ROYAL BANK OF CANADA
                                -----------------------------------------------
                                (NAME OF LENDER)

                                 By:   /s/ Stephanie Babich
                                    --------------------------------------------
                                    Name:  Stephanie Babich
                                    Title: Senior Manager


Dated as of December __, 2000