9706

Technical Data June, 2008 3M™ Electrically Conductive Adhesive Transfer Tape 9706 Product Description 3M™ Electrically Conductive Adhesive Transfer Tape (ECATT) 9706 is a pressure sensitive adhesive (PSA) transfer tape with anisotropic electrical conductivity. The PSA matrix is filled with conductive particles which allow interconnection between substrates through the adhesive thickness (the “Z-axis”) but are spaced far enough apart for the product to be electrically insulating in the plane of the adhesive. The PSA tack properties and lack of any thermal curing make Tape 9706 easy to use in assembly operations. Tape 9706 electrically connects and adhesively bonds medium pitch flexible circuits with other flexible circuits (flex), rigid printed circuit boards (PCB) or LCD screens. Tape 9706 offers good adhesion to common PCB substrates such as gold, FR-4 epoxy, Kapton™ polyimide and polyester films. Stable electrical performance in any flexible circuit interconnection application may require added mechanical reinforcement (clamping or compressing) in the bond area. Tape 9706 also electrically connects and adhesively bonds EMI/RFI shield and gaskets to metal frames and enclosures. The low contact resistance and tape construction result in good EMI performance. Tape 9706 can be applied as die cut parts or in roll form and has good adhesion to common EMI/RFI substrates such as, plated surfaces, stainless steel, and smooth gasket materials. Tape 9706 is a more surface aggressive ECATT on many substrates which will allow a higher level of adhesion build as measured via a peel adhesion test method and as compared to the 3M™ Electrically Conductive Adhesive Transfer Tapes 9703 or 9705. As Tape 9706 is a more aggressive ECATT tape, it is generally not compatible with Indium Tin Oxide (ITO) coatings or other easily corroded surfaces. Construction Property Value Adhesive Type Filled Acrylic Pressure Sensitive Release Liners Easy release liner = Silicone Treated Polycoated Kraft paper (PCK) Tight release liner = Silicone Treated Polyester liner (PET) Approximate Thickness Adhesive Liners 2 mil (50 µm) PCK = 4 mil (100 µm) PET = 2 mil (50 µm) 3 3M™ Electrically Conductive Adhesive Transfer Tape 9706 Typical Physical Properties and Performance Characteristics Note: The following technical information and data should be considered representative or typical only and should not be used for specification purposes. Adhesive Properties: Peel Adhesion to Stainless Steel: (Test Method is based on a modified ASTM D3330, 12 ipm peel rate, 1 in. width, 2 mil PET backing, 180 degree) Dwell Time @ Room Temperature 1 Hour 24 Hours 23°C 36 oz./in. (3.9 N/cm) 51 oz./in. (5.6 N/cm) Note: Peel values will often be higher than noted above when using a non-PET backing. Different backing types effect the backing modulus, thickness and stiffness and these differences directly effect the peel test result value. As an example, a 2 mil aluminum backing will change the test value of the peel adhesion as the peel back angle at the interface will change due to the backing stiffness. A 2 mil aluminum backing would generally increase the peel values. Temperature Performance1 Application Use Temperatures: -40 to +85°C in a properly designed end use application. See Note 1. Application Storage Temperatures: See “Shelf Life and Storage” comments. End user needs to qualify converted material for a broader storage environmental range. See also the Application section of this document Shelf Life and Storage Tape in roll form: Shelf life 24 months from the date of manufacture when stored in original cartons at 21°C (70°F) and 50% relative humidity. Electrical Properties: Insulation Resistance2,3 3.4 x 1014 ohms/square (estimated based on 3M™ Electrically Conductive Adhesive Transfer Tape 9703) Contact Resistance3,4 < 0.3 ohms (3M Test Method, Gold PI Flex onto Gold PCB, RT Initial R, 6 mm2) Current Carrying Capacity3,4 1 Amp/in2 estimate Minimum Gap5 Minimum Overlap Area 15 mil (0.4 mm) 5000 mil2 (3.2 mm2) 6 1. The final assembly must be tested to verify that the 3M™ Electrically Conductive Adhesive Transfer Tape 9706 can achieve the desired performance in the assembly’s end use application environmental conditions (temperature, humidity, temperature cycling, shock, application assembly design, assembly variation, etc.). Tape 9706 may achieve the -40 to +85°C temperature range (or broader temperature range excursions) in an end use application if the final assembly design is designed so that the conductive particles remain in sufficient mechanical contact between surfaces to achieve the desired contact resistance. Some type of mechanical bond line compression design as determined by the end use customer (clip, clamp, screw, compressed foam, etc.) that will apply a constant minimum pressure across the bond line may be required to meet the desired end use environmental ranges and contact resistance specification. The temperature use range is dictated by two primary items: Temperature performance of the acrylic adhesive (generally in the range of -40°C to about 95°C depending on other environmental conditions) as it supports the conductive particles in the adhesive/ particle matrix and the potential movement of the conductive fillers in the adhesive system in an end use application design. Items contributing to the performance of the Tape 9706 for resistance level performance include, but are not limited to: assembled bond line force (constant force present across the bond line after assembly and over the life of the product), types of substrates bonding, surface features in bonded area, environmental conditions, (temperature, humidity, CTE, shock, environmental cycling, etc.), assembly surfaces and Tape 9706 compatibility, Tape 9706 filler and assembly surfaces galvanic potential compatibility, etc. (See section on mechanical clamping for added information). 2. Based upon ASTM D-257. 3. Estimate based on 3M™ Electrically Conductive Adhesive Transfer Tape 9703 test data. 4. Estimated, customers are required to qualify the maximum current capability for their application. 5. Minimum free space between adjacent conductors suggested to ensure electrical isolation. Customers may qualify finer pitch performance in their applications. 6. Minimum recommended conductor overlap area (pad area) in the interconnection of individual circuit lines to ensure Z-Axis conduction. Available Sizes Slit Tape Width 0.25 to 0.5 inch (6.9 to 13 mm) 0.5 to 24 inch (13 to 609 mm) Standard Length 36 yds. (32.9 m) Maximum Length 36 yds. (32.9 m) 36 yds. (32.9 m) 108 yds. (98.8 m) Normal Slitting Tolerance 0.03125 in. (0.8 mm) (2) 3M™ Electrically Conductive Adhesive Transfer Tape 9706 Application Techniques Bonding • To obtain maximum adhesion, the bonding surfaces must be clean and dry. • Pressure must be applied to the bond line after assembly to wet the substrates with 3M™ Electrically Conductive Adhesive Transfer Tape 9706 and to engage the conductive particles with the substrates to make electrical connection. Mechanical pressure (roller, metal bar) or finger pressure at 5 to 15 psi (0.03 to 0.10 Mpa) is suggested at 20°C (68°F) to 25°C (77°F). The end user may find through testing that a higher pressure could be more effective in their end use design to meet their specific design criteria. Heat may be applied simultaneously to improve wetting and final bond strength. See Note A. • Tape 9706 is suggested to be applied at a maximum temperature range not to exceed 60°F - 158°F (15°C - 70°C). Tape application below 50°F (10°C) is not suggested because the adhesive will be too firm to wet the surface of the substrate, resulting in low adhesion. See Note A. • Adhesion builds with time, up to 24 to 72 hours may be required to reach final adhesion values. Note A) Regarding the application of Temperature, Pressure and Time (T-P-T) during assembly and/or lamination: Care must be taken by the end user during assembly as the modulus of the tape will be reduced with the application of heat. - An application method with ranges of not more than: 5-15 psi @ 15-70°C for 2-30 seconds is suggested as a set of initial evaluation ranges. An example of initial T-P-T that may be evaluated is: 8 psi applied via an assembly fixture using an air actuated pressure pad (pad is a medium firm elastomer) for 5 seconds @ 23°C. The end user may find assembly T-P-T outside these limits works well in their unique application. The noted T-P-T is a suggested starting point of tape bonding criteria and will be influenced by Tape 9706 part size, substrate types, substrate modulus, surface features, flatness, assembly fixtures, etc. - Final bond strength and conductive performance will be impacted by how Temperature-Pressure-Time interact in an end use assembly method to the desired substrates. - Care must be used to minimize excessive “Temperature-Pressure-Time” assembly methods as they are applied to the tape during assembly so that the conductive filler/acrylic adhesive matrix is not damaged leading to poor performance (ie: excessive squeeze-out of tape, filler-interface damage, minimize over compression and conductive filler/adhesive matrix damage.) - A Design of Experiments (DOE) is suggested to establish the optimum bonding conditions for each application assembly. Mechanical Clamping To assure electrical resistance stability of Tape 9706 in any flexible circuit interconnection application, or grounding application between various types of substrates, a mechanical clamp or other compressive force (i.e. foam strip held in compression over bond area.) should be considered in the design of the application. Any stress inherent in the assembly design (i.e. tensile, shear, cleavage) or temperature excursions (encountered through normal product use) applied to the bond area could result in an electrical open in the bonded circuit over time when no clamp or mechanism for maintaining a constant compressive forces is used. A well designed mechanical clamp will reduce the environmental stress on the bond line and improve the electrical reliability of the bond. In addition, the temperature operating range for the adhesive can be improved with a properly designed mechanical clamping system to ensure the conducting particles in the Tape 9706 maintain electrical contact. Several types of mechanical clamps have been used successfully including foam strips attached to lids or cases and screw-attached plastic clamps. Contact your 3M Technical Service Engineer for further information about mechanical clamping. Temperature Performance The electrical performance of Tape 9706 is more sensitive to environmental changes than is the peel adhesion performance. Contact resistance performance may be compromised, even if holding power is not significantly affected. See note 1 in “Electrical Properties” section. The user is responsible for the environmental performance qualification of Tape 9706 in their design. Rework Mechanically separate the parts using torque (for rigid parts) and peel (for flexible parts). Remove the adhesive by rubbing it off with a Scotch-Brite® Hand Pad, clean up the site, and apply new adhesive. The force needed to separate the parts and/or remove the adhesive can be reduced by softening the adhesive by heating 158°F - 212°F (70°C - 100°C) or using solvents.* *Note: When using solvents, be sure to follow the manufacturer’s precautions and directions for use when handling such materials. (3) 3M™ Electrically Conductive Adhesive Transfer Tape 9706 General Application Guide 3M has a broad line of Electrically Conductive Adhesive Transfer Tapes (9703, 9705, 9706, 9708, 9709, 9709S, 9709SL, 9712, 9713, 9714, 9719, 7805, 7810) that vary in conductive filler types, filler loading design, adhesive chemistry, storage modulus of the conductive tape, adhesion to various surface types, thickness, conformability, etc. The reason that 3M provides a variety of tape products is that the multiple products provide for a range of product attributes that allow end users more options to optimize grounding, EMI shielding and interconnect solutions. As each end use application has many variables unique to the design, it is suggested that 2 or more products be tested in a Design of Experiments (DOE) to identify the best performing product for the application along with the optimum assembly means (pressure, time, temperature, assembly fixtures, etc.) and final design configuration for desired end use performance. End use substrate surfaces will vary for many unique characteristics as will the final assembly design specification, design configuration, assembly methods and end use environmental conditions. For example: a) End use design substrates to be evaluated with the 3M™ Tapes will vary in surface energy that can impact the adhesion strength of the tape to the surfaces (Stainless Steel vs. Polyimide vs. Gold vs. Nickel plating, etc.). b) Substrate surface hardness and inherent conductivity can affect potential filler/surface contact resistance (Stainless Steel vs. Gold vs. Silver Epoxy Ink vs. plated surfaces, etc.) c) Modulus or flexibility of the substrates can affect substrate interaction with the 3M™ Tape and environmental aging performance (Rigid PCB vs. Flex circuit vs. Metals vs. substrate thickness) d) Contact area for grounding on a substrate can impact the effective contact resistance level achieved in a design (Total contact area [3mm2, 25mm2, 100mm2, etc.) and discrete sizes of individual contact areas (3mm2, 10mm2, 30mm2,etc]) e) Substrate surface topography or surface features can impact how the tape can “gap fill or conform to irregularities” and provide adhesion and conductivity between substrates. f) Bond line stress in the form of a tensile, cleavage, compression and shear can all affect 3M™ Tape performance in an application (Rigid to Rigid substrates, Multi-layer Flex to Rigid, Thin Flex to Rigid, etc.). g) Method of assembly & size of finished parts can affect tape selection (ease of converting and assembly based on die cut part shape and final assembly) h) Desired contact resistance level. For example, various applications specification may indicate a contact R