162873 (9890) 4/19/99 12:54 PM Page 1 (Process Black plate) 3 Technical Bulletin TM System Design and Performance for 3M Thermally Conductive Tapes 9882, 9885, 9890 April, 1999 Notes on System Design This publication is intended to aid the user in optimizing the design and performance and Performance of systems using 3M Thermally Conductive Tapes 9882, 9885, and 9890. Note: this information presented should be considered representative or typical and should not be used for specification purposes. The user is responsible for evaluating the tape under actual conditions of use and with the substrates intended for the users application, to determine whether the tape is suitable for a particular use and method of application. The information of this bulletin is organized in three sections: I. Thermal and Mechanical Performance Optimization Thermal impedance of the assembly Mechanical performance Minimizing entrapped air II. Performance at High and Low Temperatures Short term exposure Long term exposure Limiting factors Heat and humidity Temperature cycling III. Bond Building / Rework The bond building effect Bond building on ceramic Bond building on anodized aluminum Rework procedures Additional information on these topics or others not covered may be requested by calling the toll free number on the last page.162873 (9890) 4/19/99 12:54 PM Page 2 (Process Black plate) Technical Bulletin TM System Design and Performance for 3M Thermally Conductive Tapes 9882, 9885, 9890 I. Thermal/Mechanical Optimized thermal and mechanical performance of systems assembled with 3M Performance Thermally Conductive Adhesive Transfer Tapes 9882, 9885 and 9890 depends, Optimization among other things, on an balance of the material properties of the adhesive and the substrates and the use of assembly conditions appropriate to the parts. Thermal Impedance of the Assembly In an ideal case, substrates are perfectly flat and the bond is made without air entrapment: Adhesive Ideal, Flat Substrates In this case, thermal impedance of the bond area, R (C/W), would be equal to the tot 2 2 adhesive thermal resistance (C/in /W) divided by the bond area, A (in ). (Thermal tot resistance values typical of the 3M Thermally Conductive Tapes can be found in the Data Page.) To optimize thermal performance one would simply use the thinnest adhesive available. Substrates often will have several thousands of an inch (mils) runout of flatness of their surfaces and using the thinnest adhesive may lead to air gaps in the bond line of the assembly as represented in the edge-on view below. When both substrates are rigid materials this effect is especially likely to occur. Adhesive Non-Flat Substrates Now the adhesive no longer covers the entire area, A , rather it covers a contact area tot smaller than A and air fills the rest of the area. Calculation of total thermal tot impedance R in the case of parallel adhesive and air thermal impedances is much tot more complicated, but suffice to say the thermal impedance of the assembly is higher because of air pockets. (Please see the 3M Technical Bulletin Heat Flow Calculation for 3M Thermally Conductive Tapes 9882, 9885, 9890 for a method to determine the total thermal impedance.) Choice of an adhesive layer much thicker than the flatness runout can help reduce the air, as portrayed the bond area cross-sections Bond Area Using 2 mil Adhesive Bond Area Using 10 mil Adhesive (30% Contact, 70% Entrapped Air) (85% Contact, 15% Entrapped Air) - 2 -