Moisture Sensitive Devices (MSD) Council
Sensitive to Moisture? You're Not Alone, Join the MSD Council!
The Council meets in person at SMTA International each year to discuss the latest standards and initiatives related to MSD. If you are interested in joining the Council, contact the committee chairs.Committee Chairs:
Mumtaz Y. Bora, Peregrine Semiconductor (firstname.lastname@example.org)
Michelle Ogihara, Seika Machinery, Inc. (email@example.com)
The MSD Council is a voluntary group, under the auspices of the SMTA, dedicated to advancing the understanding and practice of moisture sensitive devices control in electronic assembly procedures and practices. Specifically, the council will serve industry professionals who are SMTA members that have an interest in moisture sensitive devices.
The MSD Council will be chartered to expand awareness through the member-secure information available on-line here and through educational programs, tutorials, symposia, publications, events for extensive networking, and possibly certification. With the increasing need for globalization in the area of industry standards, and with the understanding and proper practice of such standards, the MSD Council will also establish formal and informal relationships with international organizations that are responsible for publishing related information.
Who is involved with this group?
The Council represents engineering, production management, quality assurance and reliability, research, sales and marketing, education, purchasing, and other functions. Companies and institutions represented include electronic manufacturers and users, research laboratories, consultants, universities, component manufacturers, and manufacturers of related products.
How do I get involved?
If you are interested in serving on the Council, contact SMTA Executive Director, Tanya Martin and include your name, company, and contact information. While the information on the page below is accessible to all visitors, the information on the Self Assessment and Resources pages is accessible only to SMTA members.
Introduction to MSD Control
MSDs are electronic devices encapsulated with plastic
compounds and other organic materials. Moisture
from atmospheric humidity will enter permeable
packaging materials by diffusion and
preferentially collect at the dissimilar
During solder reflow, the combination of rapid moisture expansion and materials mismatch can result in package cracking and/or delamination of critical interfaces within the package.
These internal defects are nearly impossible to detect during the PCB assembly and test process. They lead to a number of failure modes that have a negative impact on manufacturing yields and cause early life failure of the finished electronic products.
The risk of failure during reflow is directly related to the concentration of moisture at the critical interface, which is near the centre of the package. The maximum acceptable moisture content and the rate of moisture diffusion vary for each package.
To provide suitable guidelines for assembly, the component manufacturers must categorize each new device based on how long it takes to absorb a critical level of moisture in a standard production environment.
The proper storage and handling
procedures during PCB assembly are clearly
defined in the joint IPC/JEDEC standard
J-STD-033A Standard for Handling, Packing,
Shipping, and Use of Moisture/Reflow Sensitive
Surface Mount Devices, released in 1999 and
revised in July 2002.
The standard dictates that moisture sensitive devices must be properly classified, identified, and packaged in dry bags until they are needed for PCB assembly. Once the bags are opened, each moisture sensitive device must be assembled and reflowed within a specified timeframe.
Basic proper handling requires that the total cumulative exposure time of each single reel or tray of sensitive components must be tracked through the complete manufacturing process, until all the components are placed prior to reflow.
This basic material and process control becomes very difficult to follow in a high mix production environment, when partial trays and reels are often removed and re-loaded from assembly lines to be stored in dry cabinets or dry bags.
The following issues are commonly found to cause significant levels of escape with existing manual procedures:
Additional opportunities are provided in the standard to account for dry storage under certain conditions (Short Duration Exposure) and to account for the ambient manufacturing conditions (Derating due to factory environmental conditions). Although they provide additional flexibility for the users, these rules and tables are even more difficult to implement with a manual procedure.
The table and image above were extracted from the joint IPC/JEDEC standard J-STD-033A Standard for Handling, Packing, Shipping, and Use of Moisture/Reflow Sensitive Surface Mount Devices, released in 1999 and revised in July 2002.
Top Ten Issues and Misconceptions Associated with MSD Control
|Moisture sensitive devices are a serious assembly issue that requires a high level of control. A lack of proper control will result in internal component damage during reflow due to moisture expansion. This will typically create insidious latent component defects that can escape inspection and test.||The industry standards provide a set of guidelines that are notoriously difficult to understand and challenging to implement. Simplified manual procedures tend to err on the conservative side and result in a large number of unnecessary bake cycles. This has a significant impact on lead solderability and material flow.|
The following "Top Ten" list was provided courtesy of Cogiscan and is intended to dispel certain misconceptions related to MSD control in electronics assembly.
1. In general, quality and process engineers in the PCB assembly industry have a number of misconceptions about MSD control, because they have not been formally trained on the most recent industry standards.
2. Many internal procedures are based on obsolete industry standards, such as the IPC-SM-786A and JESD22-A112. These documents have been superseded by the joint IPC/JEDEC standard J-STD-033A released in 1999 and revised in July 2002.
3. A sealed dry bag with desiccant does not require high vacuum. A simple heat seal with the proper quantity of desiccant is sufficient. High vacuum can actually be detrimental by increasing the amount of moisture diffusion through the bag.
4. The bag seal date and the 12 months minimum shelf life is not an expiration date. The decision to bake components is strictly based on the status of the humidity indicator card when the bag is opened.
5. The clock of exposure time does not always stop when previously exposed components are returned to dry storage (dry cabinet or dry bag).
6. Components that have never been exposed and get stored in 10% RH dry cabinets may have a limited storage life and exceed their critical level without ever being exposed to ambient conditions.
7. The default bake cycles have been significantly increased from 24 hours to 48 hours at 125C, and from 8 days to 79 days at 40C. A table is provided in the IPC/JEDEC standard J-STD-033A to reduce the bake cycle according to the physical parameters of each component (MSL and body thickness). To avoid degrading solderability there is a cumulative limit of 48 hours at 125C.
8. The floor life clock is not reset by reflow. Assemblers must track the remaining floor life of MSDs assembled on boards for double-side reflow and rework.
9. When factory ambient conditions exceed 30C / 60% RH, the floor life indicated on the MS label is no longer applicable. In this case the floor life must be de-rated.
10. Boards must be baked prior to rework to avoid damaging moisture sensitive components during localized reflow. The default bake cycle for populated boards is 10 days at 90C.