CircalokTM 6037 Epoxy Resin

Circalok™ 6037 is an epoxy adhesive formulated for use by the semiconductor industry. An easy-to-spread thixotropic paste, it offers high heat transfer, low shrinkage, and a coefficient of thermal expansion comparable to that of copper and aluminum. Its strong bond to a wide variety of substrates resists severe temperature cycling. This adhesive is principally used to form thermally conductive joints in fabricated heat sinks and between heat sinks and power devices. When used to bond semiconductors to heat sinks, it also serves as an electrical insulator; but the semiconductor’s mating surfaces should be precoated with E-343 and allowed to cure to insure the dielectric integrity of the epoxy interface.

 

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CircalokTM 6037 Typical Applications

Fabricating heat sinks; bonding semiconductors and transistors to heat sinks; general purpose bonding of electronic components.

Handling Instructions

Stir Circalok™ 6037 thoroughly in its shipping container to insure uniform dispersion of the filler. Weigh out the amount needed in a clean container and all the hardener by weight in the proportion specified. Mix thoroughly preferably with power equipment. To insure a void-free glue line evacuate for 5 minutes. Apply the adhesive to both mating surfaces and press together, squeezing out excess resin to obtain a thin glue line. Clamp in position to prevent movement during cure.

Handling Precautions

The labels on containers of Lord materials contain current information on the hazards associated with each particular product. Most chemicals are skin and eye irritants, and some may actually be corrosive to the skin and eyes. Other problems, such as skin sensitization or serious health hazards may exist. Further information on each product is contained in the Material Safety Data Sheet, which will be sent upon request.

Surface Preparation

Any adhesive, regardless of the type, can only be expected to perform well on a properly prepared surface. Most manufacturers will be quick to point out that such figures as "Tensile Shear Strength" were obtained on specimens tested in accordance with a certain standard. Included in the test will be preparation of the surfaces for bonding, which is usually in accordance with another standard. It would be quite possible to write a complete volume on surface preparation and still not cover every material, application or situation.

Although Lord does not purport to be an expert on all types of surface preparation, we do, nonetheless, feel an obligation to offer some suggestions to aid the user in obtaining good bond strengths.

Some surfaces require little or no preparation and epoxies will cling to them tenaciously. Other materials such as Teflon* or polyethylene are very resistant to bonding even with the best preparation methods known. In the middle of the spectrum, however, are materials, which can be bonded successfully with proper surface treatment. These would include all types of metals, many plastics, glass and ceramics.

In order to properly understand bond strengths, the user should be familiar with the difference between adhesive and cohesive failures. Assume that two pieces of metal are partially overlapped and joined by a thin bond of adhesive. Now the specimen is placed in a machine designed to pull it apart lengthwise. The stress applied is known as "shear". The point at which the specimen breaks across the bond line is known as its "Tensile Shear Strength" and is usually expressed in pounds per square inch. By examining the bond line on the two pieces, we should find that a roughly equal amount of cured adhesive is left on both pieces. This ideal condition is known as a "cohesive break". However, if we find no adhesive left on one of the pieces (or very little adhesive) this is known as an "adhesive break" and is indicative of either poor surface preparation, the wrong adhesive, a nonreceptive surface or a combination of these factors. It is important to recognize the major hindrances to adhesion. These are: DUST, DIRT, GREASE, CORROSION, OXIDATION, SCALE

In addition, smooth, nonporous surfaces generally provide poor bonds. Metals, plastics and glass, need to be artificially roughed-up to provide a good bond. Also, materials containing polyolefins or fluorocarbons will require some type of special pretreatment prior to bonding. For proper bonding, any adhesive must adequately wet the surfaces. Therefore, proper cleaning must also be considered.

In summary, we see that the two most important aspects of surface preparation prior to adhesive bonding are: PROPER CLEANING and PROPER PHYSICAL CONDITIONING.