Research On Ultrasonic Welding Of Lab-on-a-foil And Support Plate

Lab-on-a-foil is widely used in polymerase chain reaction(PCR)amplification.In order to avoid deformation during use,it is usually necessary to connect them to the support plate.For the existing polymer connection technology,ultrasonic welding has the advantages of short welding time,high strength,and little damage to the welded parts.It is hopeful that it will become an efficient connection method for the lab-on-a-foil and the support plate.Before ultrasonic welding,an energy-conducting structure needs to be made on the surface of the polymer to guide and concentrate the ultrasonic energy,but this method is complicated and inefficient,and different shapes of energy-conducting structures on the polymer have different effects on the welding strength,which increases the design difficulty of the energy-conducting structure.Based on the above problems,this paper proposes a method of making an energyconducting structure on an ultrasonic welding horn,which avoids making an energy-conducting structure on the polymer surface and achieves a good connection between the two.First,a lab-on-a-foil and support plate were fabricated.Among them,the lab-on-a-foil was composed of an aluminum foil cover sheet and a polypropylene(PP)film substrate,and the two were bonded together by an adhesive.This paper explores the thermoforming process of the film substrate,the adhesive spin coating process on the cover sheet and the bonding process.The cross section of the chip was observed by scanning electron microscope,and the results showed that the bonding state was good.The pressure test shows that the chip can withstand the maximum the air pressure is 0.45 ± 0.02 MPa,which is equivalent to the bonding strength of equivalent chips.After annealing,the warpage of the support plate decreased from 0.45 mm to 0.15 mm,which can be used for ultrasonic welding.Secondly,an energy-conducting structure was designed and fabricated on the ultrasonic welding horn,and a welding horn without an energy-conducting structure was also produced as a control.The impedance analysis and testing of the fabricated welding horn showed that the mechanical resonance frequency of the welding horn with energy-conducting structure was 19876.8 Hz,the mechanical quality factor was 2170,the mechanical resonance frequency of the welding horn without energy-conducting structure was 19928.0 Hz,and the mechanical quality factor was 2340,all of which met the requirements of engineering use.In order to verify the energy-conducting function of the energy-conducting structure,the laser displacement sensor was used to test the welding horn with or without energy-conducting structure.The result showed that the amplitude of the welding horn with the energy conducting structure was about 13 ?m,while the amplitude of the welding horn without the energy conducting structure was about 8 ?m.The increase of the welding amplitude is an important factor for the energy conducting structure to play an energy conducting role.Finally,the compression scheme of bonding PDMS elastomer on the ultrasonic welding horn was proposed,and the ultrasonic welding heat generation process of the ultrasonic welding horn with energy-conducting structure and the ultrasonic welding horn without energyconducting structure was respectively carried out by using COMSOL simulation software.Calculations showed that the temperature rise of the welding horn with energy-conducting structure was significantly higher than that of the welding horn without energy-conducting structure,and the temperature distribution was relatively uniform.The peel strength test of the soldered chip showed that the peeling force of the welding horn with energy-conducting structure was about 15.2 N,which was higher than 9.8 N of the welding horn without energyconducting structure,and the welding area was more complete,which was in line with the simulation results.Finally,the optimal welding parameters were selected according to the size of the peel strength.When the welding pressure was 0.25 MPa and the welding time was 0.6 s,the maximum peel strength was 4.31 N/mm.