Bond line thickness metals

The double shell method of roof constmction uses only about half as many metal stampings as the traditional welded assembly and gives a rigid, vibration-free product. The plastisol is effective because it requires minimal surface preparation and because bond line thickness is not critical. 

In a typical case where a silicon IC is attached to an alumina ceramic substrate that, in turn, is attached to the inside of a metal or ceramic package, the two epoxy interfaces can easily contribute 2.5 °C/watt to the total resistance. However, some silver-filled epoxies are reported to have high thermal conductivities, thus contributing 0.6 °C to 1 °C/watt. Actual measurements may differ considerably from calculated values because of reported thermal conductivities that differ from the actual, differences in the thicknesses of bond lines, voids in the adhesive, and incomplete mating of surfaces. Further in the analysis, the effects of lateral flow of heat and interactions of heat flow among adjacent components are often neglected. 

During World War II, synthetic rubber and resin-modified phenolics were used to bond aluminum sheets (available only in in. thickness at that time) into billets from which airplane propellers were carved, thus replacing laminated wood, which often shattered on impact with a bullet. Similar adhesives were used to bond rubber to metal in a variety of vibration-damping applications. The most successful widely known product of the new technology was the automotive bonded brake lining first introduced in 1947, and now regarded as a symbol of quality and integrity [12, p. 490]. 

Some applications, however, require adhesives that conduct heat but not electricity to bond power devices to heat sinks, metal substrates, or ceramic plates. The thermal transfer efficiency obviously depends not only on the thermal conductivity of the adhesive but also on the thickness of the bond line, and on the homogeneity of the adhesive layer, which must be free of voids and other defects. The addition... 

Platinum and rhodium-platinum and iridium-platinum alloys are frequently employed to line and sheath autoclaves, reactor vessels and tubes, and a wide range of equipment. Linings are generally 0-13 mm to 0- 38 mm thick, and for certain applications co-extruded platinum-lined Inconel or other metal reactor or cooling tubes are fabricated. In such cases the platinum is bonded to the base metal, but in all other instances platinum linings are of the loose type. 

There was previously a separate ISO standard for adhesion in shear but this was withdrawn in favour of extending the standard for shear modulus to allow the test to be continued to the failure point, i.e. the two methods have been combined. The composite method is contained in ISO 182715 and uses the same quadruple element test piece as did the separate adhesion standard. The double sandwich construction is intended to provide a very stiff test piece which will remain in alignment under high stresses. The present standard quadruple test piece uses rubber elements 4 1 mm thick and 20 5 mm long and these tolerances are much less tight than previously. The measured adhesion strength in shear is less affected by the test piece shape factor then tension tests8 and the wider tolerances should be perfectly satisfactory. The test piece is strained at a rate of 50 mm/min, in line with the speed for most other adhesion to metal tests, and the result expressed as the maximum force divided by the total bonded area of one of the double sandwiches. The British equivalent BS 903 Part A 1416 is identical. 

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