Preparation And Investigation On Silver-Filled Conductive Adhesive Applied In LED Packaging

Light Emitting Diode (LED), known as “Green illumination”, is a kind of solidsemiconductor devices which can provide light and many other advantages, such asenergy saving, environment protection. With the LED developing to be high power andhigh brightness, the packaging material for the LED devices are asking for higherrequirements. Silver-filled conductive adhesive is a kind of functional materials which isable to provide electrical conductivity and cohesiveness at the same time. Due to the highperformance, the adhesives are widely used for die bond process of LED packaging. Inthis paper, we studied the surface state of the commercial silver flakes, and then filled thesurface treated silver flakes to the matrix resin to form conductive adhesives. The preparedsilver-filled conductive adhesives were applied to the LED device and a series ofmeasurements were conducted.The silver flakes, which were commercial products, were analyzed by TG and DSC.Combined addition of the lubricants during the production of the silver flakes and thecorrelative literatures, we found that there is a lubricant layer coated on the surface of thesilver flakes and it had a significant influence on the properties of the silver. After readinga large number of correlative literatures, we proposed a feasible method to remove thelubricants on the silver flakes. The TGA and DSC result indicated that the lubricants onthe surface of the silver flakes were efficiently removed after the treatment. Field emissionscanning electron microscopy (SEM) analysis showed that the silver flakes became roughand uneven in the surface compared with the bright silver flakes that before the treatment.In this paper, the silver flakes were added to the polymer matrix to formed conductiveadhesives. Comparing with the adhesives which were filled with the silver flakes werewithout any treatment, the conductive adhesives which were filled with the silver flakesthat treated by the mixture of ethanol and diluted acid can remain better electrical conductivity at a relative low loading of the silver. In the conductive adhesives, thepolymer matrix provides the adhesive performance, and with the increase of the fillerloading, the proportion of the polymer matrix in the adhesive will decrease, and result inthe decline of the lap shear strength. The removal of the lubricants on the surface of thesilver flakes, make the polymer matrix in the adhesives can occupy bigger surface area ofthe flakes, and lead to the conductive adhesives receive bigger lap shear strength aftercuring. The removal of the lubricants changes the interfacial status between the silverflakes and the matrix, result in the increase of the viscosity of the conductive adhesives.The prepared electrical conductive adhesives were applied in the LED die bondprocess, and several LED samples were prepared and then tested. The results indicatedthat the adhesives had high performance and were very suitable for the LED packagingprocess, and could be further expanded production. For the independent research andpreparation of the electrical conductive adhesive, it is convenient to use and save thestorage and transport costs compare with the imported adhesive. It has highperformance-to-price ratio and could have very broad application prospect in the market.