Integration and miniaturization of electronic assemblies can be hampered by temperature sensitive components or limited in substrate options, constraining product design and assembly methods. Bonding options are limited for temperature sensitive components, especially for lower temperatures than low temperature solders. Commonly used interconnects such as anisotropic conductive adhesives (ACAs) and films (ACFs) require controlled pressure to ensure conductivity, which can damage sensitive components and substrates. ACA/ACF require longer cure times and controlled temperature, limiting production speed and scalability. Thermo-bonding requires pressure to achieve anisotropic properties which can cause damage to adjacent components or printed circuitry. This can also create a throughput bottle neck in the high volume manufacturing process Therefore, there is a need for an advanced interconnect solution to enable finer pitch connection, durability, rapid curing, and decreased manufacturing costs while maintaining consistent performance.

UV ZTACH® ACE ultra-violet cured anisotropic conductive epoxy (ACE) is a pressure-less interconnect that cures rapidly in seconds. The single step application and curing of this interconnect also provides the underfill, achieving a strong mechanical bond. The UV cure formulation does not require heat and therefore will not damage temperature sensitive components or substrates.

This material is composed of a binary adhesive resin loaded with ferromagnetic particles that have a high electrical conductivity coating. Just prior to and during the UV cure exposure, a magnetic field is applied using SunRay’s patented ZMAG® Magnetic Pallet, forming alignment of the ferromagnetic particles into columns. These z-axis, vertical columns provide a low electrical resistivity connection between component pins and substrate pads, through the thin bond line thickness of the epoxy, while maintaining electrical isolation laterally between pads.

In contrast to previous TechBlick conferences where SunRay Scientific has presented on its thermally cured ZTACH® ACE, this presentation will focus on the novel Ultraviolet (UV) light-curable version to meet the market needs of pressure-less, non-thermal bonding with a scalable, high throughput capable process. As with the thermally cured solution, this material can be stenciled or dispensed for quicker throughput and processing. Due to the nature of the ACE’s z-axis column formation, the deposit areas cover the entire device footprint versus requiring intricate patterns. Alignment is less stringent than needed for more expensive, precision patterned tools. Short exposure to UV in the presence of the magnetic field for curing allows for faster processing over thermal curing, minimizes fixturing and movement, important for precision assemblies such as fine wires or finer pitch connections.

The presentation will overview UV-cured ZTACH® ACE material’s current capabilities for components sizes, relative to “shadow-curing” – that is, the UV-curing of the epoxy in the light starved portion of devices. Case studies to be discussed include assembly of temperature sensitive surface mount technology (SMT) batteries, bonding to low temperature flexible substrates, fine wire attach assemblies and other unique electronic assembly challenges.

UV-cured ZTACH® ACE material and processing reshapes current electronic assemblies via single-step packaging of mixed electronic components that otherwise cannot survive elevated pressure and high temperature during assembly. Additionally, lower profile component attachment is enabled on flexible substrates, reducing product rigidity and thickness, integrating assemblies, and enabling further miniaturization. This emerging anisotropic conductive epoxy is compatible with SMT lines’ sheet-to-sheet (S2S) processing, while a UV-curable ZTACH® ACE is particularly desirable for scaling in roll-to-roll processing. With additional process development, this approach will enable low cost, high through assembly options for temperature sensitive assemblies.