How to classify Moisture Sen-sitivity Surface Mount Devices (SMDs) is a daily conversation at every semiconductor, assembler and OEM in the world. When the question, "What additional temperatures are needed to test packages with the new lead-free finishes?" was asked, the answers differed from each supplier and customer. Industry-wide confusion prevailed. The long awaited answer is finally here. The new USA Moisture Sensitivity classification J-STD-020B revision is maintained under the joint standards efforts of the IPC and JEDEC. The July 2002 revision is found at either ipc.org or jedec.org. Avoiding Damage This revised standard still has its eight levels, as shown in the table. The purpose of '020B is to identify the moisture sensitivity level at a fixed reflow temperature. Tagging the temperature will enable the user to properly store and handle the SMDs to avoid subsequent thermal/mech-anical damage during assembly reflow attachment and/or repair operations.
The lower the level of classification, the longer the floor life. The packages are classified generally to the lowest level for moisture sensitivity and the highest reflow temperatures possible to give OEMs the largest process window when mounting package to board. The primary stumbling block for this revision was to set the temperature required for the lead-free process. Would it be 240°, 245°, 250°, 255°, 260°C or greater? The dedicated work of several companies, consortia and standards committee (IPC and JEDEC) task groups led to creating the lowest possible reflow temperatures to meet the lead-free challenge.
The standardized lead-free temperatures create tighter process windows because the melting point of the lead-free alloys-compared to the peak reflow temperature-is decreased by at least 25% over lead/tin alloys. This decrease will challenge EMS companies and OEMs to process the lead-free products cost-effectively within these new ranges. Just Published, but Changing The JEDEC and IPC task groups know that this standard is dynamic in nature. And just because Revision B was only published this August does not mean that the next revision will not have to begin soon.
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