Intel's Packaging Databook Chapter 8: Moisture Sensitivity/Desiccant Packaging/PSMCs Handling
This chapter examines surface mount assembly processes and establishes preconditioning flows which encompass moisture absorption, thermal stress and chemical environments typical in the variety of surface mount assembly methods currently in use. Also discussed are the standardized moisture sensitivity levels which control the floor life of moisture/reflow sensitive PSMCs along with the handling, packing and shipping requirements necessary to avoid moisture/reflow related failures. Baking to reduce package moisture level and its potential effect on lead finish solderability is described. In addition, drying, shipping, and storage procedures are included. 8.2 Moisture Sensitivity of PSMCs
This section addresses technical issues related to maintaining package integrity during board level assembly processing using Plastic Surface Mount Components (PSMC). Surface mount processing subjects the component body to high temperature and chemicals (from solder fluxes and cleaning fluids) during board mount assembly. In through-hole technology the board assembly process uses wave soldering which primarily heats the component leads. The printed circuit board acts as a barrier to protect the through-hole package body from solder heat and flux exposure taken by both supplier and user to minimize the effects of reflow solder stress on the component. Plastic molding compounds used for integrated circuit encapsulation are hygroscopic and absorb moisture dependent on time and the storage environment.
Read the full Packaging Databook, Ch. 8.