The vast majority of RFIC devices used in cellular phones and wireless infrastructures are made of GaAs substrates. GaAs material is most competitive for high frequency, high speed and/or low power consumption for components such as power amplifiers and switches. For other specific wireless applications other materials such as SiC, InP or LiTaO3 substrates are used.
For the dicing of RFIC’s manufacturers are facing several challenges that are time consuming, operator intensive and result in a high cost:
- Fragile GaAs wafers: the typical RFIC wafer is a brittle, 100 um thick, 6 inch GaAs wafer. (most of the 4 inch are converting to 6 inch). Wafers may break during several manufacturing or handling steps which results in wafer yield loss.
- Different dicing technologies are used for different substrate materials.
- Backstreet etching : Most of the applications have several microns of Au backmetal on the wafer. Backside street etching and/or trenches are required for mechanical dicing processes.
- Thick (eg flipchip wafers) : new assembly methods, different interconnection methods or device performances require thicker wafers, which require significant modifications to dicing principles.
- Dicing yield and assembly yield due to dicing operation : the traditional mechanical technologies create small cracks and chipouts that may result in dicing yield issues, which often only appear during final packaging or testing, despite extensive inspection after dicing.
- Multi-project wafers (MPW) wafers usage is very inefficient since the majority of the wafer is wasted since only continued dicing kerfs can be made.
The multibeam laser dicing enables significant improvements:
Basically a 100% dicing yield and assembly yield (due to dicing) since no mechanical forces (contact less dicing process) are applied.
Reduction of dicing time of 1 hour or more to several minutes only.
Eliminate the need for backside street etching or trenches.
Productivity per operator increases by factor 3 – 5.
The dicing streets can be minimized to as low as 25 µm on a typical 100 um GaAs wafer.
The laser dicing allows a basically 100% wafer yield for broken or cleaved wafers, as well as MPW wafers.
One dicing process and system for several wafer substrate materials and different thicknesses on the same system creates flexibility and high equipment utilization.
The multibeam laser dicing for thin GaAs in combination with ALSI’s proprietary post processing technology based on wet-etching offers exellent die strength (fracture strength), all fitting into the existing infrastructure utilizing standard materials such as dicing tape and normal assembly steps.
A 100 µm thick GaAs RFIC wafer (after stretching):
pitch 1525×2125 µm
full Au on backside
street width 30 µm
total dicing width ≤ 17 µm