Molding materials for lead-free components packaging are different from traditional epoxy materials in two aspects: slower moisture absorption and better resistance to higher temperatures. But at the high temperatures required to melt lead-free solders, components become very hot, and almost all absorbed moisture quickly turns into steam, causing damage to the component. In addition, the huge difference in thermal expansion coefficient of packaging materials can also cause electrical damage. In various cases, damage can range from small delamination to large visual defects, such as bursting from the bottom of the core to the top surface of the epoxy package.

        The new IPC/JEDEC J-STD-020D standard provides manufacturers of electronic components and systems with specific defect guidelines and definitions to help them avoid problems with the final product. The standard was revised in June 2007 to provide information for manufacturers to test and grade their components and determine their humidity sensitivity levels. These levels can assist PCB assemblers to ensure that components can be soldered to PCB within the set floor life time and reflow temperature profile limits.

         During the set floor life time, the component does not absorb too much moisture to cause problems. The D-version standard provides a temperature curve for staged reflow of lead-free solders and specific absorption requirements for plastic-encapsulated compounds prior to testing, which can be prepared to withstand higher temperatures of lead-free reflow soldering. (Reflow soldering temperature curve defines the relationship between temperature and time when PCB passes through reflow furnace.

        The new standard also provides some test specifications, which specify necessary environmental conditions for the preprocessing of packaging devices. Therefore, component and system manufacturers begin with the same definition when modifying their processes to produce reliable products.

        Determine humidity sensitivity level

        In order to determine the humidity sensitivity level embodied in the current J-STD-020D standard, the researchers exposed surface mounted components to specific environmental conditions, simulated the installation of these components on a PCB, and used a specific classification reflow temperature curve to make the PCB through a reflow furnace three times. Researchers used an ultrasound microscope to obtain pre-processing and post-processing images, which recorded the original defects and welding defects respectively, such as cracks, delamination or voids. Researchers from Intel, IBM, NXP, Agere and other semiconductor manufacturers have carefully completed these tasks. Therefore, standards have been created.

        IC manufacturers can use these same tests to classify their components, and these PCB assemblers can determine how to handle specific types of IC.

         The information in Table 1 is extracted from the J-STD-020D standard, which represents the floor life time of the component with eight humidity sensitivity levels. Floor life time represents the time between removing components from moisture-proof packaging and reflow soldering of components. The longer a device stays in the manufacturing environment, the more moisture it absorbs.

         For components meeting J-STD-020D standard, the manufacturer can add suffixes on the package label to list the humidity sensitivity level of the component and the manufacturer's allowable peak temperature of the package. For example, floor life time of stage 3 components is 168 hours at a maximum temperature of 30℃ and a relative humidity of 60%. In addition, floor life time specifications cover devices manufactured using traditional compounds and high temperature plastic-encapsulated compounds.

         In developing standards, researchers rely on experience to determine appropriate reflux temperature curve parameters and absorption time, which can be used by IC vendors and PCB assembly companies to test components intended for assembly lines. Absorption conditions set the time for components to be exposed to specific humidity and RH levels before testing.

         Tests include baking elements removed all moisture, and then "absorption" is performed under a standard condition of a certain level selected according to the "absorption requirements" in Table 1. Before testing, stage 3 components need to be absorbed for 192 hours (+5/-0 hours) at 30℃ and 60% RH. In order to determine whether the defect is caused by wet or reflow environment, components must be inspected before and after reflow welding.