Effect of the laser parameters, epoxy mold compound properties and mold tool surface finishing on mark legibility of encapsulated IC package

Abstract

Changing of quality requirement in manufacturing technologies has to be followed by an adaption of material and process parameters. With the rapid emerging vision inspection technologies, 100% automated optical inspection as quality firewall is always a preferred option to pursue. In the case of transition from human to automated optical inspection to enhance defect detectability, the adaption effort is high due to different capabilities between human and machines on observation and interpretation of the criteria. This will strongly affect the justification of acceptance level which will subsequently cause over or under rejection. For encapsulated IC, the challenges are not only on the ability to detect the defect but also to recognize the laser marking character printed on the surface of the mold compound, which are used as traceability and identification purpose.A theoretical concept is being described to get a grasp of the occurring mechanism. From laser mark aspect, respective factors such as marking depth range coupled with correct marking size with respect to the field of view (FOV) are identified as major contributor for mark legibility. From material point of view, the compatibility of wax type (ratio of hydrophilic and hydrophobic parts) towards multi aromatic resin (MAR) or multifunctional resin (MFR) is identified as the cause of the flow mark or wax stain which eventually contribute the noise of visual inspection. Also from material aspect, types of flame retardant either metal hydroxide or organic phosphorous cause low curability which affects the molded package surface evenness eventually affect visual inspection results. From mold tool aspect, the range of lower roughness average (Ra) of the Electrical Discharge Surface (EDM) mold cavity surface is preferred for better mark legibility. At the end, a proposal is given on parameters, material and tool set to get the best encapsulated IC package surfaces with clear and legible marking. The constraints and corresponding potential risks are also discussed in this paper in order to achieve the best results yet not induce other negative impact.