<PAGE>

EXHIBIT 4.12

                              SECURED DEMAND NOTE

                              HTM HOLDINGS, INC.

     THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
     AMENDED (THE "ACT") AND MAY NOT BE SOLD, ASSIGNED, PLEDGED OR OTHERWISE
     TRANSFERRED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
     ACT COVERING THE TRANSFER OR AN OPINION OF COUNSEL ACCEPTABLE TO THE ISSUER
     THAT SUCH REGISTRATION UNDER THE ACT IS NOT REQUIRED.


US $636,080.12                                                  Denver, Colorado
                                                                    July 3, 2000


     FOR VALUE RECEIVED, the undersigned HTM Holdings, Inc., a Delaware
corporation (the "Company"), hereby promises to pay to each of the payees set
forth on Schedule 1 hereto or its registered assigns (each, a "Payee"), on
demand at any time made by the Payees holding more than 50% of the aggregate
principal amount then outstanding hereunder, the principal sum set forth
opposite the name of such Payee on Schedule 1 hereto, together with interest of
(i) a lump sum of 3% of such principal amount accruing on the date hereof and
(ii) simple interest from the date hereof on such principal amount at a rate of
13.75% per annum, in lawful money of the United States of America in immediately
available funds.

     Any and all payments by the Company under this Note shall be made free and
clear of and without deduction for any and all present or future Taxes. If the
Company shall be required by law to deduct any Taxes from or in respect of any
sum payable hereunder, (i) the sum payable shall be increased as much as shall
be necessary so that after making all required deductions (including deductions
applicable to additional sums payable hereunder) each Payee shall receive an
amount equal to the sum it would have received had no such deductions been made,
(ii) the Company shall make such deductions and (iii) the Company shall pay the
full amount deducted to the relevant taxing or other authority in accordance
with applicable law. Within thirty (30) days after the date of any payment of
Taxes, the Company shall furnish to each Payee the original or certified copy of
a receipt evidencing payment thereof. The Company shall indemnify and, within
ten (10) days of demand therefor, pay each Payee for the full amount of Taxes
(including any Taxes imposed by any jurisdiction on amounts payable hereunder)
paid by such Payee, and any liability (including penalties, interest and
expenses) arising therefrom or with respect thereto, whether or not such Taxes
were correctly or legally asserted.

     Payment of this Note by the Company to each Payee is secured pursuant to
the Security Agreement of even date herewith between the Company, SMTC de
Chihuahua S.A. de C.V., a Mexican corporation, and each Payee.


can investors Mex Secured Note
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     The Company hereby waives diligence, presentment, demand, protest and
notice of any kind whatsoever. The nonexercise by the holder of any of its
rights hereunder in any particular instance shall not constitute a waiver
thereof in that or any subsequent instance.

     Terms defined in the Note Purchase Agreement of even date herewith between
the Company and the Payees and not otherwise defined herein are used herein with
the meanings so defined.

     This Note shall be construed in accordance with and governed by the laws of
The Commonwealth of Massachusetts without giving effect to principles of
conflicts of laws.


                              HTM HOLDINGS, INC.


                              By: /s/ Paul Walker
                                 ------------------------
                                 Name: Paul Walker
                                 Title: President


can investors Mex Secured Note
<PAGE>

                                  Schedule 1
                                  ----------


Payee                                                Principal Amount
-----                                                ----------------
Kilmer Electronic Group Limited                      US $636,080.12



can investors Mex Secured Note