Thermosets uses , features , advantages and disadvantages
The thermosets are ideal for high-heat applications such as the electronics & the appliances , They have the polymers which cross-link together during the curing process to form the irreversible chemical bond and the process can eliminate the risk of product remelting when heat is applied .
Thermoset materials enhance chemical resistance , the heat resistance & the structural integrity , They can improve the material’s mechanical properties and the thermoset plastics are used for sealed products due to their resistance to deformation .
The thermoset plastics are more resistant to high temperatures than the thermoplastics , They have highly flexible design , They offer thick to thin wall capabilities , The offer excellent aesthetic appearance , They come with high levels of dimensional stability & they are cost-effective .
The thermosets do not display this reversible change behaviour , During the polymerisation ( curing ) , The thermoset polymers form links or chemical bonds between the adjacent chains , The result is a three‐dimensional network that is much more rigid than the two‐dimensional ( linear ) thermoplastic structure .
The interlinked chains are not free to move when heat is applied & the thermoset is set into the permanent rigid shape , The level of cross‐linking can be varied , The materials with high cross‐link densities are hard , rigid & often brittle , The thermosets with low cross‐link densities can be softened by heating to high temperatures but they do not melt ( like a thermoplastics ) & their original shape is maintained .
The thermosets like phenolic & epoxy resins have a long history as circuit board and packaging materials , For many wet-paste applications , The thermosets are preferred because they have low solvent content & wet-paste processes for bonding fiat surfaces large in the area & They can be accommodated without difficulty .
Wet-paste processes are established , especially for die-attach & manufacturing equipment , including dispensers and screen printers and it is designed essentially to accommodate thermoset pastes .
Spin‐coating of fiat substrates (e.g. semiconductive wafers) can now be done with thermoplastic pastes ‐ not previously practical before with thermosets , Dry film processes using sheets , ribbon (reels) or preforms have been restricted due to the limitation in availability of different materials , notably thermosets .
While thermoset films have been used for substrate attach , their use has been restricted in the main to hybrid microcircuits mainly due to limitation in convenience , Processing & performance .
Preforms can now be conveniently used for special components such as semiconductor devices (Si and GaAs) , crystals and SAW devices , In addition, complex shapes and patterns can be fabricated as preforms , using hard tooling or laser cutting/profiling techniques .
Attaching with thermoset/epoxy pastes has been done by depositing wet-paste onto the substrate die sites (pads) and then placing the device into the wet-paste , The assembly would then be placed in a heating oven to polymerise (cure) the adhesive and form a permanent bond .
The advantage of thermoset paste is that it is a one‐step process and it is conventionally accepted as the de facto standard , The advantage of thermoplastic paste , pre‐staged or thermoplastic film/preforms is that you control the bond‐line thickness & uniformity more easily , Wet paste process can be difficult due to the dome shaped profile of the deposition .
Thermoset pastes are still the preferred option mainly on tradition but also on equipment availability , Die attach equipment from prominent suppliers are now being adapted to cope with thermoplastic adhesives , with special features for handling film preforms and ribbon .
The thermoset plastics can not be recycled , They are more difficult to surface finish , They can not be remolded or reshaped .