In part II of our series, we cover the SCOPE and BACKGROUND, APPLICABLE DOCUMENTS, ORDER OF PRECEDENCE, QUALITY ASSURANCE PROVISIONS, THERMAL STRAP REQUIREMENTS, DELIVERY, AND DESIGN OF THERMAL STRAPS topics when drafting your thermal strap specification.

Thermal Strap Specifications - Part II

1. SCOPE AND BACKGROUND 

1.1. Statement of scope. This specification establishes the performance, design, test, manufacture, acceptance and qualification requirements for thermal strap assembly.

1.2. Background information. If helpful and allowed, add some information about what this thermal strap is going to do and in what context. A picture of the notional strap and its surroundings is helpful.

2. APPLICABLE DOCUMENTS (typical, there may be others) 

• MIL-DTL-5541 - Chemical Films for Aluminum and Aluminum Alloys

• ASTM E595 - Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment

• SAE-AMS--QQ-A-200/8 - Aluminum Rod and Bar, Extruded, 6061-T6

• SAE-AMS-QQ-A-225/8 - Aluminum Rod, Bar, Wire or Shapes, Rolled, Drawn or Cold Finish, 6061-T6

• ISO 9001-2008 - Quality Management Systems Requirements

• AS9102 - Aerospace First Article Inspection Requirements

(These documents must be provided for the proposal effort. Relevant section(s) within the documents should be explicitly referenced.)

3. ORDER OF PRECEDENCE

In case of any conflicting requirements, the following order of precedence shall apply:

• Purchase order

• This specification

• Source Control Document(s)

• Reference documents

• TAI internal specifications

4. QUALITY ASSURANCE PROVISIONS 

4.1. Product assurance provisions. A product quality assurance (QA) program or quality management system (QMS) shall be established that meets the requirements of ISO 9001:2008. 

(Additional requirements shall be specified during the proposal effort (i.e. RFP). Failure to specify all QA/QMS provisions within the RFP may delay the program start or result in a change order during the execution of the contract.)

4.2. Responsibility for inspection. Unless otherwise specified, the manufacturer shall be responsible for the performance of all inspection requirements as specified in 

Section 5.2. Unless otherwise specified, the manufacturer shall utilize his own or any other facilities suitable for the performance of the inspection requirements specified herein. 

Customer reserves the right to perform or witness, at the manufacturer's facility, any of the inspections set forth in this specification when such inspections are deemed necessary to assure supplies and services conform to prescribed requirements. Source inspection of the thermal straps / thermal links may be imposed on procurements to this specification, at the discretion of 

(must be specified during the proposal effort)

4.3.Thermal Strap Qualification. Qualification shall be accomplished by the Customer through successful operation of the Thermal Strap assembly during higher assembly qualification tests. Piece-part qualification is typically not required or provided.

4.4.Quality conformance inspection. The quality conformance inspection shall consist of the tests and inspections specified in Section 5.2. Thermal strap assemblies failing these tests and inspections shall not be shipped against this specification. 

4.5.Methods of examination and test. TAI shall establish test methods that provide accurate measurements to the satisfaction of Customer. These methods should be reviewed and either accepted or modified during the proposal phase.

(If the customer requires review and approval of test procedures, this must be specified during the proposal effort)

4.6.Sampling plan. All tests and inspections shall be performed at the 100% level on each thermal strap assembly, except the dimensional and materials inspection. Dimensions and materials shall be verified at First Article Inspection.

4.7.First Article Inspection (FAI). (If required) FAI will be done in accordance with AS9102. Customer is to mark this specification and any other governing documents with the items to be covered by FAI. Ensure Customer QA is consulted to ensure adequacy and accuracy of the FAI.

5. THERMAL STRAP REQUIREMENTS

5.1.Non-binding: The following requirements are levied on TAI to be designed for, but not tested nor inspected by TAI as part of item acceptance. Either analysis by TAI or historical evidence shall be acceptable to demonstrate compliance; otherwise the Customer will perform the testing post-delivery.

5.1.1. Thermal Conductance. TBD W/K minimum for the thermal strap /  unit alone, not including interface resistance to the customer’s equipment or to TAI’s test setup. The performance specification shall include manufacturing variability and changes in thermal properties of the materials over the system operating temperature range specified.

(This is listed as non-binding because it typically cannot be measured directly. TAI tests conductance between heater block and sink block, using estimates of the losses due to the interfaces. Thermocouples taped to the side of the thermal strap are typically not reliable enough to prove conductance. Thermocouples embedded within the end fittings would be reliable enough for a direct measurement, and can be done if this is required. Further, TAI does not have the test equipment to test at temperatures other than room temperature. Thermal conductance at high or low temperature will be estimated using material conductivity data versus temperature.)

5.1.2. Relative Motion. Specify how much motion will be required of the end fittings either during installation or operation.

5.1.3. Axial random vibration. When tested as specified, the thermal strap assembly shall show no physical damage and shall continue to function within tolerance. Acceptance, Flight Proof, Protoqual, and Qualification vibration levels and durations are defined in TBD.

5.1.4. Radial random vibration. When tested as specified, the thermal strap assembly shall show no physical damage and shall continue to function within tolerance. Acceptance, Flight Proof, Protoqual, and Qualification vibration levels and durations are defined in TBD.

5.1.5. Shock. When tested as specified, the thermal strap assembly shall show no physical damage or permanent change in characteristics after exposure to the shock profile that produces the shock response as required by TBD. The shock shall be applied once independently along three mutually perpendicular axes.

5.1.6. System operating temperature. The operational temperature range shall be TBD. The thermal strap assembly shall be designed to perform within specifications while operating within its system operating temperature range.

5.1.7. System non-operating temperature. The non-operating temperature range shall be from TBD. The thermal strap assembly shall be designed to perform within specifications after exposure to TBD thermal cycles plus TBD vacuum cycles over the non-operating temperature range.

5.1.8. Cleanliness. TAI shall design the thermal strap assembly in a way to prevent particle generation and allow cleaning as much as possible.

(The assemblies will be delivered as clean as possible, but not to any cleanliness specification. Any specific cleaning (e.g. vapor degreasing) shall be performed by the customer after item acceptance.)

5.2.Binding: The following requirements are levied on TAI and are to be tested or inspected by TAI as part of item acceptance. 

5.2.1. Item definition. Define what is meant by one “thermal strap (or Thermal Link) assembly.” 

5.2.2. Materials. The material for the thermal strap assembly shall be as specified below. When a definite material is not specified, a material shall be used which shall permit the thermal strap assembly to conform to the requirements of this specification. Material and process traceability shall be provided by TAI. 

5.2.2.1. End fitting material. The terminal material shall be aluminum in accordance with SAE-AMS--QQ-A-200/8, or SAE-AMS-4027. 

5.2.2.2. End fitting surface treatment. The terminal shall be chromate treated per MIL-DTL-5541, Type I, Class 1.

5.2.2.3. Conductive fiber material. Thermal strap material shall be TAI-proprietary GraFlex™ graphite fiber from TAI stock.

5.2.2.4. Epoxy. The epoxy used to bond the thermal strap material to the end fittings shall be the TAI-proprietary Condux™ thermally conductive epoxy.

5.2.3. Outgassing. All nonmetallic materials shall be tested for outgassing in accordance with ASTM E595. Materials shall exhibit a total mass loss (TML) of not more than 1.0 percent and a collected volatile condensable material (CVCM) of not more than 0.1 percent. Historical data and data listed in the NASA Reference Publication 1124 for applicable materials may be used in lieu of actual testing.

5.2.4. Marking. The thermal strap assembly shall be legibly marked, as a minimum, with the Customer part number and serial number. 

(Customer to specify information, location, and method)

5.2.5. Measured Thermal Conductance. TBD W/K minimum. This measured thermal conductance shall include the effects of a bolted interface to the test fixture, unless otherwise specified. The net thermal conductance shall be measured at an atmospheric pressure of 1 x 10-3 Torr or less and the thermal sink at approximately room temperature (30 °C). 

5.2.6. Max Weight. The weight of a thermal strap assembly shall be TBD grams maximum.

5.2.7. Max Stiffness. The maximum stiffness of each thermal strap shall be TBD N/mm (lbf/in) in any direction from nominal installation position.

6. PREPARATION FOR THERMAL LINK DELIVERY

6.1.Data Package. The following items shall either accompany delivered parts, or be delivered separately (specify):

• Proof of accepted FAI (if required)

• Inspection results (if required)

• Test results / certifications (specify)

• Certificate of conformance - A certificate of conformance shall be supplied with each thermal strap assembly certifying that no change in the dimensions, materials, or manufacturing methods has been made without prior written approval from Customer.

6.2.Thermal Strap Assembly Packaging. Each thermal strap assembly shall be packaged individually, in a way to preclude damage during shipping and handling. Containers shall be marked with the following identification (specify):

• Complete Customer part No., Revision, and Name

• Date of Manufacture

• Purchase Order Number

• Manufacturer's Name and Address

6.3.Exterior package marking. Multiple units may be packed in a single shipping box. Exterior of shipping containers shall be marked with the following identifications (specify):

• Complete Customer part No., Revision, and Name

• Purchase Order Number

• Manufacturer's Name and Address

• Number of Thermal Straps in Container

• Country of origin

7. DELIVERY OF THERMAL STRAPS

Specify address and acceptable shipping method(s).

8. POST DELIVERY

8.1.Customer testing and schedule

8.2.Acceptance criteria (if any)

8.3.Acceptance schedule (no later than 30 days post-delivery)

9. NOTES

10.INTERFACE CONTROL DRAWING(s)

(include ICD(s) with relevant dimensions only, marked up for FAI)