Injection moulding integration of a red VCSEL illuminator module for a hologram reader sensor
2007
A red VCSEL illuminator module demonstrator was manufactured by injection moulding integration. A red VCSEL
chip was first attached to a simple FR4 substrate, which contains bonding pads and conducting wires for the VCSEL
chip attachment and electrical driving. The substrate was then placed as an insert in an injection mould. The VCSEL
chip shielding and optics formation was made in a one-step injection moulding process. The used optical thermoplastic
in the processing was polycarbonate (PC). The pursued optical function of the single spherical surface attained in the
moulding was to collimate the emitted red light (l=664.5 nm) from the VCSEL chip.
The main critical issue related to the manufacturing of the illuminator module in the injection moulding process was the
durability of bonding wire contacts. A single 25 mm diameter gold wire was used in wire bonding in order to create the
upper contact to the chip. The lower contact was processed by attaching the chip to the substrate using conductive
epoxy. A test series of 20 modules using FR4 substrate materials were produced. The number of fully operative modules
was 12 resulting total module yield of 60%. The main reason for a non-operative module was loosening of the bonding
wire during the injection moulding process. The bonding wire durability in the moulding process can be improved by
using glob-top shielding of the VCSEL device before injection moulding and using a lower holding pressure in the
injection moulding process.
A diamond turned insert was used in the mould in order to create a high quality lens surface on the top of the VCSEL
chip. The tower average length after one iteration round by mould modification was 8.676 mm, so the measured value
was on average 20 mm larger than nominal value. The measured RMS roughness of the processed lens surface was 5 ...
7 nm and the radius -3.23 ... 3.83 mm. The radius of the lens and the length of the tower varied depending of the used
process parameters.
The manufactured illumination module can be integrated with a CMOS image matrix sensor in order to form a compact
hologram reader system. The injection moulding integration principle seems to be very promising method to
manufacture intelligently integrated and cost-effective optoelectronic products according to experience with this
demonstrator.
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