As devices such as cell phones, cameras, and tablets continue to shrink, there is also a big push to shrink the thickness of these devices, and hence the thickness of the dies and wafers, says AI Technology Inc (AIT) of Princeton Junction, NJ, USA (which provides materials and adhesive solutions for electronic interconnection and packaging). Wafers and substrates are thinned down from as much as 750μm down to 25-50μm to improve the performance and/or provide a thinner and lighter electronic device.
While back-grinding tapes are used in many applications in place of traditional wax solutions, a temporary bonding wax that can be applied to the thickness of 10μm still provides many advantages over the thicker back-grinding tapes, particularly for more aggressive processes and more fragile wafers, says the firm.
Responding to this need for thinner wafers and substrates, AIT has developed a series of temporary wax-like media that has been proven to be useful in many of these thinning applications. Unlike traditional wax, AIT’s wax-like media provides well-defined melting points of 80oC and 160oC for different processing requirements and easy removal. The bonding medium can be dissolved cleanly with IPA or acetone. AIT says that its temporary bonding media have been proven useful in all of the four primary methods for wafer thinning: mechanical grinding, chemical mechanical polishing (CMP), wet etching and atmospheric downstream plasma (ADP), and dry chemical etching (DCE).
AIT’s back-grinding liquid wax (BGL) can be spun to form 10μm film for precision bonding with a die-shear bond strength of over 500psi for temperatures 15oC below the melting point. The firm provides the temporary bonding/protective wax in pre-dissolved isopropyl alcohol (IPA). The thickness of this wax film can be adjusted in the spin coating process or by diluting the wax liquid further with IPA.
One of AIT’s feature Temporary Bonding IPA-Soluble Wax Solutions, BGL7080, can be heated to 60oC and still maintain a stable bond. Other high-temperature waxes, such as BGL70160-HV and BGL7080-HV7, can maintain a relatively stable bond up to 135oC and 150oC, respectively. These waxes can withstand exposure to high temperatures up to 225oC for shorter time periods without degradation.
Release or dismount is achieved by melting the wax at a high temperature to lower the viscosity of the wax layer significantly, allowing the release of the wafer or device mechanically by lifting or gentle sliding.
For high-temperature waxes, IPA or other solvents must be used to swell, penetrate, soften, and dissolve the waxes. This can be done by dipping and soaking the wafer/substrate into an IPA bath. Warm IPA at 40-60oC will accelerate this dismount mechanism.
AIT says that it has developed its temporary bonding/protective wax solutions by working with customers to meet their specific needs. The firm can also formulate a solution that will work for a customer’s stringent requirements.
