Transcript Popcorning


Moisture Sensitive Devices

A Real Production Problem
Background





Moisture and Surface Mount Components do not mix
Plastic packaging material very often is permeable to
moisture
If moisture permeable plastic packaging material
levels become critical, component damage may occur
when subject to reflux temperature (popcorning)
Moisture induced failures are often undetectable,
causing malfunction within 2 and 6 months
Higher processing temperatures of unleaded solder
will exacerbate the problem
Lead Free and Popcorning
Quelle: Intel
Popcorning



The epoxy moulding compound used in most plastic
encapsulated devices is hygroscopic
While processing, temperatures up to 260º C are
applied
Fast ramps and high temperatures prevent moisture
from escaping
Popcorning


This leads to delaminating the encapsulated
interface of the die, resulting in a gas bubble
This is not always visually apparent
Popcorning


Exceeding the technical elastic limit results in cracking
of the plastic packaging, water vapour escapes with a
sudden burst
The plastic packaging has a „leak“ permeating oxygen
slowly destroys the components
Popcorning
Popcorning Example 1

BGA device,
showing crack
between
fibreglass
substrate and
plastic body
moulding
Popcorning Example 2

QFP device,
showing crack
on top of plastic
body moulding
Popcorning Example 3

Micro section
through BGA
device, showing
delaminating
and crack
through
conductive
adhesive and
fibreglass
substrate
Popcorning Example 4

BGA device,
showing crack
between
fibreglass
substrate and
plastic body
moulding
Popcorning Example 5

QFP device,
showing crack
on the
underside of
the plastic
body moulding
IPC-Levels for IC`s
Quelle: IPC
IPC-Levels for IC`s
Quelle: Intel
Component Humidity
Quelle: Intel
Absorption
Quelle: Intel
Absorption
Quelle: Intel
Traditional Prevention




Historically components and printed control boards
have been backed to remove moisture
Typically temperatures from 40 to 125 C and times
of between 1 hour and 1 week have been used
This adds time and a monetary cost to production
Backing is still possible, only according to IPC
spec
Problems with Baking





Surface solder ability is degraded
Growth of inter metallic layers is promoted, also
with low temperature (40 degree C
Baking is only possible one time (IPC)
Ovens can be expensive to run
They take up valuable space on the production
floor
Solder Ability
SOIC 14 Chip, 60/40 Sn/Pb alloy, type R flux, as received
Time to Zero
Wetting Times
0.58
0.56
0.54
0.52
0.50
0.48
0.46
0.44
0.42
1
2
3
4
5
6
7
Sam ple Num be r
8
9
10
Solder Ability
SOIC 14 Chip, 60/40 Sn/Pb alloy, type R flux, 4 hours @ 100 C
Wetting Times
0.82
Time to Zero
0.80
0.78
0.76
0.74
0.72
0.70
1
2
3
4
5
6
7
Sam ple Num be r
8
9
10
Solder Ability
SOIC 14 Chip, 60/40 Sn/Pb alloy, type R flux, 4 hours @ 100 C
SOIC 14 Chip, 60/40 Sn/Pb alloy, type R flux, as received
Time to Zero
Wetting Times
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
1
2
3
4
5
6
7
Sam ple Num ber
8
9
10
Inter Metallic Growth




Total inter metallic thickness has shown to increase by
approximately 50% when baking at 125 C is used for 4
days
In the case of a copper metallisation, this is mainly the
Cu6 Sn5 layer but all layers are effected
Inter metallic growth is a function of time and
temperature
The thicker inter metallic layers can lead to a reduction
in solder joint integrity and in extreme cases reduce
solder ability
Alternative Prevention

Use a Drying Cabinet
No reduction of solder ability as no heat is involved
Oxidisation is prevented by diminishing humidity
All moisture is removed by a recycling desiccant
drying system
Lower operating cost (compared to baking)
Efficient use of factory floor space
Variety of Dry Storage




Moisture Barrier Bags
Nitrogen Cabinets
Dry Air Boxes
Desiccant Dry Cabinets
Pros / Cons of MBB Storage
Cons
Pros

Inexpensive start up, little
investment required

Bags can/do remain
unsealed for extended
periods

Silica Gel packets used
‘’past their prime’’

Silica Gel packets
improperly stored

Labor intensive
Pros / Cons of Nitrogen
Cabinets
Cons
Pros


N2 often available
N2 cabinets familiar







Often poorly maintained
Rarely monitored for
effectiveness
Costly to operate
Installing is necessary
Not available everywhere
Very pure N2 is needed to dry
components, expensive!!
Can hardly dry components
Comparison of Costs using N²
· Assumptions
Costs of N² ~ 0.19 € / m³
Power costs ~ 0.06 € / KWh
average N² consumption ~ 25 L / min
Purchase costs of Totech Dry Cabinet ~ 7 600.00 €
· Arising expenses from a N² cabinet
Consumption : 25 l / min, i.e. 1 080 000 l / month, i.e. 1080 m³ / month
Costs: 205,20 € / month, i.e. 2462.40 € / year
· Arising expenses from a Totech Drying Cabinet
Consumption : 0.056 kW / h, i.e. 40.32 kW / month
Costs : 2.42 € / month, i.e. 29.09 € / year
Saving of costs within one year: 2 433.31 €
This is equivalent to 37.5 months refinancing (Purchase costs: 7 600.00 €) only
by the N² consumption of a nitrogen cabinet (~ 3 years)
(The calculation excludes installing the nitrogen cabinet and leasing costs for N² bottles.)
Drying Cabinets
History of Drying Cabinets
1974 - First auto-recycling dry cabinet developed for
commercial use utilizing Silica Gel, regularly being
dried by a heating system
1976 First use of synthetic zeolites (as molecular sifter )
in dry cabinet designs, replacing Silica Gel
1982 New dryer design capable of managing ultra-low
humidity levels, patented (Totech, Japan)
1987 Texas Instruments, with primary applying of ultralow humidity dry cabinets for MSD storage.
Before that, dry cabinets were only used for the optics
industry and consumer goods
Pros / Cons of Desiccant
Dry Cabinets
Pros







Dries without use of heat
Fast de-humidification
Zero maintenance
Constantly monitored for
effectiveness
Low cost operation
Air tight
Mobile
Cons

Higher initial investment
required
Recommendation for
Time of Drying
HSD-Series
SDE-Series
At the same
temperature,
the drying
time is equal
to backing
time according
to IPC
reference.
Dry Cabinet Acceptance

App. 200.000 Dry Cabinets sold every year
extensive residential use in Asia
JAPAN 75%
EXPORT 25%



App. 10.000 ‘less than 5% RH’ cabinets sold
every year worldwide
A total of 8-10 desiccant dry cabinet
manufacturers worldwide
Increasing demand in Europe (lead-free)
Dry Cabinet Suppliers

8-10 large suppliers worldwide

Cabinet should at least go to 5% RH
Great majority of cabinets built for the
residential market (i.e.. 30-50% RH)
The demand for ultra-low humidity is growing


Various Dry Cabinet
Applications




CSP, BGA, QFP
etc
Printed Circuit
Boards

Crystal Resonator

Optical Fiber, CCD
etc

(LCG) Liquid
Crystal Glass
Wafers
Ceramics
IPC/JEDEC 033a Application
Dry Cabinet at 10% RH


MSD packages not sealed in a MBB may be placed
in a dry atmosphere cabinet, maintained at not
greater than 10% RH. These dry cabinets should not
be considered a MBB
Storage of MSD packages in these dry cabinets
should be limited to a maximum time per Table 7-1. If
the time limit is exceeded they should be baked
according to Table 4-2 to restore the floor life
IPC/JEDEC 033 Application
Dry Cabinet at 5% RH


MSD packages not sealed in a MBB may be
placed in a dry atmosphere cabinet, maintained at
not greater than 5% RH
Storage in these dry cabinets may be considered
equivalent to storage in a MBB with unlimited shelf
life
How do they work?
Functional Principles



An interlocked fan causes the air to circulate
through the dry unit
While passing through the dry unit moisture in the
air is absorbed by the zeolite desiccant
During periodic rejuvenating of the zeolite
desiccant by heating, the absorbed humidity is
evaporated and exhausted through the external
shutters of the dry unit
Function of Dry Unit
(Moisture
being
exhausted
during
recycling
period)
Zeolite




Synthetically produced zeolite A
47% open space
High rate of absorption at low RH
levels
Excellent ability to regenerate
Functional Principle
To ensure a minimal inflow
of outside ambient air the
interlocked fan is stopped
automatically when a door
is opened
(Extra Feature on Super-Dry)
Functional Principle
After the doors are closed,
the fan begins operating
again to accelerate the
moisture absorption inside
the air tight Drying Cabinet
Calibrating
Calibrating is
possible by
exchanging
the complete
Humidity
Sensor
Maintenance
Recommendation


Running time of the interlocked fan is interrupted
(30% on). Still the fan is subject to abrasion,
esspecially concerning the bearings
To garantee good functioning the fan must be
changed after the indicated time of operational
performance
(Triple operational performance by interruption enables about 10
years of functioning)
Basic Requirements


Must recover within an ‘‘acceptable‘‘ period of
time after being accessed
Must maintain a constant RH level once
recovery is complete
Intermittent Control after
Door Opening
Control Accuracy
Increase of Humidity
during Blackout
Features of SD und HSD







Convenient Digital Control Panel
ON/OFF calliper on frontside
Infinitaly variable humidity setting
Automatic resetting temperature display
Alarm function when doors are left open
Delayed humidity alarm with LED
Key Lock Function for the Digital Control Panel to
prevent unintended changes of setting
SD-Series
Humidity Appearance
HSD-Series
Equipped with two Dry Units
Humidity Appearance
Drying efficiency of
different Cabinets
Minimize Recovery Time by:

Improving MSD administration / control

Additional drying units (2 or 3)

Forced air circulation (fan interlocked with doors)

Heated air

Nitrogen Purge

Short door opening times
Cabinet Size and
Configuration

Number of doors does not relate to number of
separate ‘‘environments‘‘

Smaller doors bring about shorter recovery times

Typically same desiccant dry units in all models

Cabinets should be only as large as required
Option: Data Logging
Function

Measuring of humidity and temperature with internal storage up to 16.000 measured values (8.000 recordings
including date, time, humidity and temperature)

Limit value monitoring for both measurement categories
Inputs

internal sensor for humidity and temperature

Humidity measuring range:
0 ... 90 % humidity (resolution 0.5%; accuracy +/- 3%)

Temperature measuring range: -30 ... +50 °C (resolution 0.5 °C; accuracy ± 1 K)
Configuration

By Micro Lab Plus Software

Selectable looping time for reading storage: between 10 sec and 2 hours

Adjustable limit values for both measurement categories
Display and appliance

LC - Display 2 digit for instantaneous values or MIN/MAX values

Double calliper operation for all adjustments
Communication

RS232 standard interface

Infrared interface
Supply

Internal lithium battery 3.6 V TL5101, exchangeable

Battery durability approximately 2 years
Housing

Plastic, degree of protection according to IP65

Dimensions 72 mm x 23 mm; weight 55 g
Option: Datenlogger
Option: Alarm


Alarm Buzzer /Light if
door is open longer
than 90 sec
Alarm Buzzer /Light or
SMS-Alarm when
humidity exceeds the
RH level set value
longer than a specified
time
Option: Reel Rack
Option: Reel Rack
DubbleReel-Rack
on ball
bearing
move out
Option: Shelf Dividers
Option: Nitrogen Purge

Continuous stand-by for
amounts from
0 -20 l/min

Automatic initiation to
purge the cabinet ( max
100 l/min) after closing
the doors

Timer to reduce the
nitrogene consumption
Special Purpose
Solutions
Summary
It is important to provide




Comprehensive ESD
protection
A closed loop feedback
from sensors
Forced air circulation
Use of a good dessicant
(zeolites with open
surface structure)