An Independent Journal Dedicated to the Advancement of Chip - Scale Electronics July - August 2000 Email the editor

How to classify and handle moisture sensitive surface mount devices is a daily discussion topic in every semiconductor company and OEM in the world. The more moisture sensitive the SMD is, the more costly it is to handle.
	By Mark Bird Contributing Editor

Moisture Sensitivity

The USA Moisture Sensitivity Classification (J-STD-020A) and Handling (J-STD-033) standards are the two specifications that have the greatest impact on SMDs. These standards are maintained under the joint standards efforts of the IPC and JEDEC. The April 1999 revisions of these standards can be found at the JEDEC web site www.jedec.org.

The present moisture sensitivity standard contains the seven levels shown in the table. The purpose of this standard is to identify the moisture sensitivity level at a fixed reflow temperature, so that the user can properly store and handle the SMDs to avoid subsequent thermal/mechanical damage during the assembly reflow attachment and /or repair operations.

The lower the level, the longer an SMD's floor life. The goal of all package manufacturers is to have their packages reach Level 1, which would be an unlimited floor life.

Reflow Temperatures

The present moisture sensitivity classification uses two reflow temperatures, 220^oC and 235^oC to classify packages. The packages are classified generally to the lowest level for moisture sensitivity, and to the highest reflow temperatures possible, to give the OEMs the largest process window when mounting the packages to boards.

The second standard's purpose is to provide SMD manufacturers and users with methods for handling SMDs. These methods are provided to avoid damage from moisture absorption and exposure to reflow temperatures that may result in yield and reliability degradation.

These two standards are very important and are widely used in the industry. It is already time to revise both documents. The Joint Task Group of IPC and JEDEC has began revision activities in Tempe, Ariz., in February.

The major factor driving the changes stems from the requirement for moisture sensitivity classification to add a third reflow classification temperature of 260^oC. This new, higher temperature is being added to accommodate the higher temperature profiles needed for some lead-free mounting applications.

This higher temperature requirement will definitely make the classification of current packages a real challenge at any classification level.

Many of the present SMD packages may drop two, three or more levels when subjected to the higher 260^oC temperature. It is important to provide as much industry support as possible to the JEDEC and IPC task groups to ensure a useful and productive specification revision is created.

Contact your representative if you can add value to this critical update. The Joint Task Group is targeting late 2000 or early 2001 for publishing the next revisions of the standards, therefore little time remains.