Investigation of the flow properties of adhesives in electronic packaging

Adhesives in electronic packaging processes are applied in finer and finer structures and in very small quantities. The quality of adhesives is accompanied by the growing requirements on their application, such as screen and stencil printing, stamping and inkjet. The application of adhesives depends on their rheological behaviour. Technical data sheets give viscosity values that have been determined using simple, standardised analytical methods. It is impossible to select an adhesive for an application on the basis of these values alone. Even today, it is still necessary to test the adhesives directly in the application process. This is a complex and time-consuming procedure and does not produce any transfer results. The key to overcoming these problems lies in the rheology of adhesives. The quality of applying an adhesive is crucially influenced by its flow behaviour. In the past, the rheological behaviour of adhesives was under investigation for screen and stencil printing and was described and published in a previous paper. This work is continued and focuses on adhesive application in stamping and ink jet printing thereby taking account of the rheological behaviour. Different adhesives were used in these studies. The application behaviour and the evenness of the deposits were evaluated. The flow behaviour of the adhesives was characterised in detail. Adhesives for inkjet printing with Newtonian flow behaviour with and without polymer additives were investigated. For the application by stamping, a correlation was found between storage modulus and loss factor on the one hand and the adhesive amount transferred on the other. This paper presents some of the research results obtained for stamping and inkjet concerning the correlation between the rheological properties of adhesives and their application behaviour. The critical rheological value is indicated and characterised.