Adhesive remains strong after reflow cycles for reliable operation

Industrial adhesive manufacturer, Delo, has introduced Delo Monopox TC2270, a thermally conductive, electrically insulating and humidity resistant adhesive.

It shows good strength, even after standardized humidity tests with subsequent reflow cycles are performed, said the company for fast heat transfer and long-term reliable operation of semiconductors in power electronics.

A common reason that power semiconductors fail is because heat develops in their extremely small components with no place for it to dissipate,explained Delo. By using Monopox TC2270, a permanent bond and electrical insulation is created yet heat is able to dissipate.

Due to its ceramic filler, aluminium nitride, Delo’s one-component, heat-curing epoxy resin provides very high thermal conductivity of 1.7 W/(m∙K) – measured to ASTM D5470. This is comparable with silver-filled isotropic conductive adhesives (ICA), which have a thermal conductivity of around 1.5-2.0 W/(m∙K), reported Delo.

One advantage to using Delo Monopox TC2270 over ICA is that it provides both heat dissipation and electrical insulation of assemblies. The electronic adhesive additionally allows proportionate component costs to be reduced, added Delo.  After it has been cured, Monopox TC2270 has a compression shear strength of 34 MPa on the FR4 composite material and 11 MPa on high-performance LCP plastics. When bonding microchips, the adhesive reaches values of 60 N in the die shear test (1.0 x 1.0mm² silicon dies on gold surface).

The adhesive also shows good strength after standardised humidity tests. To determine the moisture sensitivity level (MSL 1), silicon dies were bonded to different PCB materials, stored for one week at 85 degrees C and 85 per cent air humidity, and then subjected to three-consecutive reflow cycles. The adhesive retained its high strength level with these loads, noted Delo.

To enable the bonding of temperature-sensitive assemblies and prevent them from damage caused by excessive curing temperatures, the adhesive is designed with a chemical system, ensuring that final strength is reached after 90 minutes at a curing temperature of 60 degrees C. With a temperature of 80 degrees C, the curing process can be completed in 15 minutes. That way, production processes can be individually adapted to the component types and quantities to be manufactured. The adhesive’s service temperature range is between -40 and +150 degrees C.

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