Bond line thickness is one of the important factors to be considered in designing a bond joint. Most commonly used bond line thicknesses in a bond joint range from about 0.001 to 0.007 inches. The performance of an adhesive in an application depends on the overall properties of the adhesive, the substrates being bonded, surface preparation on the substrates, the bond line thickness, and the uniformity of the bond line. Generally, a thin bond line is preferred over a thick one, since the stress concentration at the corners of the joint is lesser in a thinner bond line. Also, the air cavity concentration is lesser in a thin bond line as compared to a thick one.
In a bond joint, it is very important to have a uniform bond line thickness for optimal adhesive performance. Shim spacers can be used for keeping the bond line thickness uniform. In many cases, solid glass microspheres of different sizes (~0.001 to 0.007 inches) can be added to the adhesive to create a uniform bond line thickness.
Master Bond can offer custom formulated, glass beads filled adhesives (one and two component), with different viscosities, to meet the exact spacing requirements. These adhesives enhance the consistency, reliability, functionality, and cost effectiveness, in various electronics, optical, aerospace, and medical applications. Master Bond also offers film adhesives, for achieving uniform bond thickness. Two such film adhesives are: FL901AO, a thermally conductive and electrically insulating film and FL901S, an electrically conductive film. The standard bond thickness for both films is 0.003 inches. However, they can be formulated in custom sizes and thicknesses.