Research On Reliability Of IR&PD Match Pair For IR Touch Screen

Recently,the large-sized Infrared Touch Screen rapidly develop and widely apply to education,conference,entertainment or other fields,due to the advantage of high light transmittance,good environment adaptability,long lifespan and cost performance.According to the prediction of authoritative organization,infrared touch screen will keep fast increasing in the next years.As the key component of infrared touch screen,the IR&PD match pair plays a key role in transmitting and receiving infrared signal to realize the function of fixed position,requires a high consistency of photoelectric parameter performance and reliability to assure the long lifespan of the infrared touch screen.In this paper,we study how to improve the reliability of IR&PD match Pair from the perspective of application,combining with the actual failure cases.The basic knowledge of IR&PD match Pair is systematically introduced from theory,package structure,material,parameter characteristics and process techno logy,as well as common,failure modes and mechanisms.The analysis,verification process and final conclusion,improvement measures of two typical failure cases,including open circuit and light attenuation are elaborated.In terms of LED open circuit failure problem,we decayed and observed the samples to find out the direct cause of open circuit is the gap between lead frame and silver paste.After that,we analyzed the three potential factor-epoxy,lead frame,silver paste one by one.We used common way such as DSC?TMA?and stress and strain to test epoxy,and analyzed the plating of lead frame by using SEM,EDS and FTIR.After excluding these two factors,the reason is locked into the abnormal adhesive force of silver paste.In order to reappear the failure phenomenon which is consistent with customer failure products,we simulated all kinds of abnormal technological conditions that may exist in the actual production of silver paste.We found that the uneven mixing of silver paste is the root cause for the abnormal adhesion and the failure of the product.Finally,we formulated the improvement measures,which effectively avoid the recurrence of open circuit.In terms of light attenuation problem,we analyzed several failure factors,including reduction of the reflectivity of the lead frame,the excessive light absorption of the silver paste,the decrease of the epoxy transmittance,and the degradation of the chip power.We used the FTIR?SEM?and EDS to analyse the lead frame plating,sliver paste and epoxy of the failure samples and good samples,excluding the above factors.After that,we ground and sliced the samples,through the SEM scan we found that the failure chip exist cracks which penetrate the PN junction.At the same time,through the thermal resistance test,it was found that the thermal resistance of the PN junction of the defective product was significantly larger than that of the good product.Therefore,it was inferred that chip cracking was the direct cause of light attenuation,and epoxy stress was the root cause of chip cracking.In order to confirm this inference,we compared the DSC test and found that the epoxy resin of the defective product was not cured enough,resulting in excessive internal stress to the chip.For this reason,we arranged a simulation experiment to reproduce the failure phenomenon consistent with the defective product by accelerating the aging,thereby confirmed the inference that the insufficient curing of the epoxy leads to excessive stress which damages the chip and causes light attenuation.Finally,in response to this problem,we have formulated improvement measures in terms of processes and interceptions to effectively prevent the recurrence of such problems.The research on reliability of the IR&PD match pair,and the analysis and verification process of open circuit and light attenuation,help us have a deeper understanding of the material,process,performance and reliability of the product.These studies have important guiding role and reference value for the reliability of the IR&PD match pair and even the conventional LED products.