I don't understand the expression " technical appointment letter". Generally every appointment letter is an official order issued by the employer to the selected candidate for any job under him. Normally it should contain the designation or job position of the appointee, the compensation package offered with break up of various components, all applicable fringe benefits of employment, leave benefits, the period of probation and the confirmation, the notice of the termination of contract of employment from either side, a general note of strict adherence to the rules of discipline of the organization etc.
I don't think it necessary to include all the technical details of the job and make it look like a bond or exhaustive agreement.