Voiding Control of Lead-Free Soldering at Quad-flat No-lead package Components

the quad-flat no-lead (QFN) package design is widely applied in many new applications due to benefits including small size, reduced lead inductance, and good thermal and electrical performance. However, it remains challenging to control thermal pad voiding under QFN due to the large coverage area and low standoff. Many parameters, such as solder paste flux type, powder size, powder quality, surface finish, and component size can impact voiding behavior. In addition, process parameters such as stencil design, printing, and reflow also have a strong impact on voiding. In this work, reflow profile, reflow atmosphere, solder particle size for different type of solder paste flux on organic solderability preservative (OSP) substrate were evaluated. Results of investigation indicate that void was decreased with increasing temperature above liquidus (TAL) and peak temperature. Solder paste flux type effects were strong and reflow atmosphere effects were moderate for 96.5Sn3.0Ag0.5Cu (SAC305) Type 4 powder, both of which increased for SAC305 Type 5 powder.