<PAGE>

                                                                   EXHIBIT 10.19

                 EIGHTH AMENDMENT TO LOAN AND SECURITY AGREEMENT

      THIS EIGHTH AMENDMENT TO LOAN AND SECURITY AGREEMENT (this "Amendment") is
entered into as of the 25Th day of June, 2004, by and between LASALLE BANK
NATIONAL ASSOCIATION, a national banking association (the "Bank"), and SMT
UNLIMITED L.P., an Illinois limited partnership (the "Borrower").

                              W I T N E S S E T H:

      WHEREAS, Bank and Borrower entered into that certain Loan and Security
Agreement dated as of August 25, 1999, as amended by that certain Amendment to
Loan and Security Agreement dated as of December 17, 1999, that certain Second
Amendment to Loan and Security Agreement dated as of September 8, 2000, that
certain Third Amendment to Loan and Security Agreement dated as of October 26,
2000, that certain Fourth Amendment to Loan and Security Agreement dated as of
February 16, 2001, that certain Fifth Amendment to Loan and Security Agreement
dated as of July 10, 2002, that certain Sixth Amendment to Loan and Security
Agreement dated as of February 27, 2003 and that certain Seventh Amendment to
Loan and Security Agreement dated as of July 9, 2003 (collectively, the
"Agreement"), and now desire to further amend such Agreement to, among other
things, (i) renew the Revolving Credit Commitment, (ii) include certain amounts
receivable of Solectron (as defined below) as Accounts Receivable under the
Revolving Loan Borrowing Base and (iii) amend certain financial covenants.

      NOW, THEREFORE, for and in consideration of the premises and mutual
agreements herein contained and for the purposes of setting forth the terms and
conditions of this Amendment, the parties, intending to be bound, hereby agree
as follows:

      1.    Incorporation of the Agreement. All capitalized terms which are not
defined hereunder shall have the same meanings as set forth in the Agreement,
and the Agreement, to the extent not inconsistent with this Amendment, is
incorporated herein by this reference as though the same were set forth in its
entirety. To the extent any terms and provisions of the Agreement are
inconsistent with the amendments set forth in Paragraph 2 below, such terms and
provisions shall be deemed superseded hereby. Except as specifically set forth
herein, the Agreement shall remain in full force and effect and its provisions
shall be binding on the parties hereto.

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

            (a)   The definition of the terms "Solectron" and "Solectron
Eligible Accounts Receivable" are hereby added to the Agreement to read in their
entirety as follows:

            "Solectron" means [Solectron], a company organized under the laws of
            Malaysia.

            "Selectron Eligible Accounts Receivable" means an Account Receivable
            generated by Solectron which otherwise satisfies all of the terms
            and conditions for being classified as an Eligible Account
            Receivable, with the exception of subsection (ix) contained in such
            definition of Eligible Account Receivable. For

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            purposes of such determination, any references to the Borrower
            contained in the definition of Eligible Account Receivable shall be
            deemed to refer to Solectron.

            (b)   The definition of the terms "Maturity Date", "Revolving Loan
Borrowing Base," "Revolving Note" and "SigmaTron Guaranty" are hereby amended
and restated to read as follows:

            "Maturity Date" means July 31, 2005.

            "Revolving Loan Borrowing Base" means, as at any date of
            determination thereof, an amount equal to the lesser of (i) the
            amount then available under the Revolving Credit Commitment and (ii)
            an amount equal to the sum of (A) eighty-five percent (85%) of the
            net amount of Eligible Accounts Receivable outstanding at such date;
            (B) fifty percent (50%) of Eligible Inventory at such date and (C)
            fifty percent (50%) of the net amount of Solectron Eligible Accounts
            Receivable outstanding at such date; provided, however, that (x) the
            aggregate amount of advances for Eligible Inventory shall not exceed
            One Million Five Hundred Thousand Dollars ($1,500,000) at any time
            and (y) the aggregate amount of advances for Solectron Eligible
            Accounts Receivable shall not exceed Five Hundred Thousand Dollars
            ($500,000) at any time.

            "Revolving Note" means, that certain Substitute Revolving Note dated
            as of June 25th, 2004 in the maximum principal amount of THREE
            MILLION DOLLARS ($3,000,000), as the same may be amended, modified
            or restated from time to time, and together with any renewals
            thereof or exchanges or substitutes therefor.

            "SigmaTron Guaranty" means that certain Guaranty dated as of August
            25, 1999 made by SigmaTron in favor of Bank, as amended by that
            certain Reaffirmation of and Amendment to Guaranty dated as of
            December 17, 1999, that certain Second Reaffirmation of and
            Amendment to Guaranty dated as of September 8, 2000, that certain
            Third Reaffirmation of and Amendment to Guaranty dated as of October
            26, 2000, that certain Fourth Reaffirmation of and Amendment to
            Guaranty dated as of February 16, 2001, that certain Fifth
            Reaffirmation of and Amendment to Guaranty dated as of July 10,
            2002, that certain Sixth Reaffirmation of and Amendment to Guaranty
            dated as of February 27, 2003, that certain Seventh Reaffirmation of
            and Amendment to Guaranty dated as of July 9, 2003 and that certain
            Eighth Reaffirmation of and Amendment to Guaranty dated as of June
            25th, 2004, as further amended, modified or restated from time to
            time.

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            (c)   Paragraph 11.2(f)(i) is hereby amended and restated to read as
follows:

            Maintain minimum Pre-Tax Income of at least the following amounts as
            calculated for the periods set forth below:

<TABLE>
<CAPTION>
                  Period                                           Amount
                  ------                                           ------
<S>                                                               <C>
May 1, 2004 through July 31, 2004                                 $200,000
May 1, 2004 through October 31, 2004                              $500,000
May 1, 2004 through January 31, 2005                              $700,000
May 1, 2004 through April 30, 2005 and                            $900,000
each trailing twelve months period ended thereafter
measured as of the end of each fiscal quarter of
Borrower
</TABLE>

            (d)   Paragraph 11.2(f)(ii) is hereby amended and restated to read
as follows:

            Maintain Tangible Net Worth, at all times, of at least the following
            amounts for the periods set forth below:

<TABLE>
<CAPTION>
                    Period                                         Amount
                    ------                                         ------
<S>                                                             <C>
July 31, 2004                                                   $2,200,000
October 31, 2005 and at all times thereafter                    $2,400,000
</TABLE>

            (e)   A new Paragraph 11.2(h) is hereby added to the Agreement to
read in its entirety as follows:

            (h) Compliance with Federal Laws. Borrower shall (a) ensure, and
            cause each Subsidiary to ensure, that no person who owns a
            controlling interest in or otherwise controls Borrower or any
            Subsidiary is or shall be listed on the Specially Designated
            Nationals and Blocked Person List or other similar lists maintained
            by the Office of Foreign Assets Control ("OFAC"), the Department of
            the Treasury or included in any Executive Orders, (b) not use or
            permit the use of the proceeds of the Loans to violate any of the
            foreign asset control regulations of OFAC or any enabling statute or
            Executive Order relating thereto, and (c) comply, and cause each
            Subsidiary to comply, with all applicable Bank Secrecy Act ("BSA")
            laws and regulations, as amended. As required by federal law and
            Lender's policies and practices, Borrower shall promptly cooperate
            with Lender's requests to obtain, verify and record certain customer
            identification information and documentation in connection with
            opening or maintaining accounts or establishing or continuing to
            provide services.

      3.    Representations and Warranties. The representations and warranties
set forth in Paragraph 11.1 and all covenants set forth in Paragraphs 11.2 and
11.3 of the Agreement shall be deemed remade and affirmed as of the date hereof
by Borrower, except that any and all

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references to the Agreement in such representations, warranties and covenants
shall be deemed to include this Amendment.

      4.    Closing Conditions. Prior to entering into this Amendment, Bank
shall have received the following documents, each in form and substance
satisfactory to it:

            (a)   Substitute Revolving Note executed by Borrower;

            (b)   Eighth Reaffirmation of and Amendment to Guaranty executed by
SigmaTron;

            (c)   Seventh Reaffirmation of and Amendment to Subordination
Agreement with D.S. Patel;

            (d)   Seventh Reaffirmation of and Amendment to Subordination
Agreement with SigmaTron;

            (e)   Resolutions of the General Partner of Borrower approving this
Amendment; and

            (f)   Such other documents, certificates and opinions as Bank shall
request.

      5.    Fees and Expenses. Borrower shall pay or reimburse Bank for all
costs, fees, and expenses incurred by Bank, or for which Bank becomes obligated,
in connection with the negotiation, preparation, and closing of this Amendment,
together with all attorneys' fees, search fees and taxes payable in connection
with this Amendment.

      6.    Effectuation. The amendments to the Agreement contemplated by this
Amendment shall be deemed effective immediately upon the full execution of this
Amendment and without any further action required by the parties hereto. There
are no conditions precedent or subsequent to the effectiveness of this
Amendment.

      7.    Counterparts. This Amendment may be executed in two or more
counterparts, each of which shall be deemed an original, and all of which
together shall constitute one and the same instrument.

                            [SIGNATURE PAGE FOLLOWS]

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                      (SIGNATURE PAGE TO EIGHTH AMENDMENT)

      IN WITNESS WHEREOF, the parties hereto have duly executed this Eighth
Amendment as of the date first above written.

                                  SMT UNLIMITED L.P., an Illinois limited
                                  partnership

                                  By: SMT Unlimited, Inc., its General Partner

                                     By: /s/ Gary R. Fairhead
                                        ----------------------------------------
                                     Its: Vice President

      Accepted as of the 25th day of June, 2004, at Bank's principal place of
business in the City of Chicago, State of Illinois.

                                  LASALLE BANK NATIONAL ASSOCIATION

                                  By: /s/ Sara A. H. Huizinga
                                      ------------------------------------------
                                  Its: Assistant Vice President

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