Laser microwelding of polystyrene and polycarbonate

Abstract

Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer based MEMS. One method of laser welding that offers great promise of success is Through Transmission Infrared (TTIr) welding. TTIr works by passing a laser through one of the components to be joined and focusing it on the second which has an absorbing material (such as carbon black) added to it. In the following studies, the radiation from a 1 W laser diode (850 nm) was fiber coupled to a lens that focused the beam to a spot size of either 25 or 50 µm. Polycarbonate and polystyrene samples were welded by scanning the beam across the samples at rates from 8 to 60 mm/s. It was possible to generate welds below 15 µm in width. Some of the other key findings included: 1. Tensile testing of micro-welds is difficult because of problems with peeling 2. When rectangular samples were sealed (welded) the welds were hermetic and able to sustain burst pressures as high as 0.50 MPa 3. A distributed heat source model can accurately predict temperature fields in plastic laser welds 4. Distributed heat model predicts weld widths more accurately than point heat source models 5. For micro-welding of plastics, when the dimensionless distribution parameter is less than two, a point heat source model predicts similar widths to those predicted by a distributed heat source model 6. At relatively high travel speeds (>100 mm/s), the distributed model predicts a location within the plastic that experiences two peak temperatures 7. At relatively low power levels, (∼50 mW) it is possible to heat PC so that visible, temporary deformation occurs. Additional findings included the confirmation that the following observations made in traditional laser welding were also seen in micro-welding of plastics:At relatively higher heat input ablation can occur which reduces weld strength independent of weld width.Thermoplastics offer significant advantages in the fields of biomedical engineering, communications, and in particular applications related to Micro Electro Mechanical Systems (MEMS). For example, the low manufacturing costs of polymers may allow industry to fabricate disposable MEMS. Rapid, consistent, and inexpensive assembly or packaging is critical to the commercialization of polymer based MEMS. One method of laser welding that offers great promise of success is Through Transmission Infrared (TTIr) welding. TTIr works by passing a laser through one of the components to be joined and focusing it on the second which has an absorbing material (such as carbon black) added to it. In the following studies, the radiation from a 1 W laser diode (850 nm) was fiber coupled to a lens that focused the beam to a spot size of either 25 or 50 µm. Polycarbonate and polystyrene samples were welded by scanning the beam across the samples at rates from 8 to 60 mm/s. It was possible to generate welds below 15 µm in width...