MSD Council Meeting at SMTAI 2011
Tuesday, October 18 | 2:00pm | 204A
Fort Worth Convention Center, Fort Worth, TX
FREE to All Attendees!
Officers:
Mumtaz Y. Bora, Peregrine Semiconductor
Steve Martell, Sonoscan
Michelle Ogihara, Seika Machinery, Inc.
Agenda:
Industry Standards for Moisture Sensitivity Packages
- Update J-STD 033B.1
- J-STD -020D.1
Package Handling/Baking/Packaging Guidelines
PWB Handling/ Baking/Packaging Guidelines
- Updates – IPC 1601 Standard
Controls at PWB/Assembly Site
Summary/Q&A
Purpose
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. |
Charter
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.
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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.
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If
you are interested in serving on the Council,
contact SMTA administrator JoAnn Stromberg 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.
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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
material interfaces.
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.
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 The following issues are commonly found
to cause significant levels of escape with
existing manual procedures:
Clearly identify the trays and reels
containing moisture-sensitive devices.
Maintain a log sheet of cumulative exposure
time associated with each tray and reel.
Maintain the association between the log sheet
and the individual trays and reels.
Maintain an acceptable level of data
integrity/quality during manual logging and
date/time calculations.
Keep track of the remaining floor life and
expiration of MSDs while they are loaded on
placement machines.
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
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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.
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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.
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