Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 2M

• Die attach is the traditional method for attaching a die to a package.
• The goal of a die attach process is to provide a 100% void-free attachment between the die and package, which would minimize heat resistance, and a die attach material that has no outgas, which may contaminate a MEMS device.
• Two approaches for die attach are epoxy adhesive and eutectic die attach.
• The epoxy die attach utilizes epoxies with different fillers depending upon the desired conductivity (silica filler for insulating, silver for conducting) and cure temperature (typically, <150°C).
• An issue with epoxy die attach may be outgas during and after curing; this may contaminate a MEMS device.
• This contamination can affect MEMS devices by causing stiction and have an impact on device reliability.
• Research has developed a low outgas epoxy [40] that may meet the requirements for MEMS devices.
• The epoxy may be automatically dispensed in a pattern in the package; the die handled by a vacuum pick-up will insert the die onto the epoxy pattern in the package die attachment area in the package well.
• Appropriate space on the device layout will need to be provided to facilitate the automated vacuum pickup.
• The eutectic die attach layer, such as gold-silicon (AuSi) or tin-lead (SnPb), is reflowed to provide a mechanically strong bond that conducts heat and electricity well.
• The consideration for use of a eutectic die attach is the high-temperature processing (183°C for SnPb or 379°C for AuSi).
• The eutectic die attach does not have the outgas concerns of the epoxy die attach.