dm00094059

AN4351
Application note
EnFilm™ micro battery EFL700A39 automatic or semi-automatic
mounting on PCB
Introduction:
STMicroelectronics has developed micro battery products (EnFilm™) with reduced
thickness and weight.
This document provides recommendations for automatic mounting of the EnFilm™
micro battery EFL700A39 on printed circuit boards (PCB) for evaluation as well as for
production purposes.
The mounting process uses mono-component polymers with low curing temperatures
compatible with the use of EnFilm™ micro batteries.
September 2013
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Contents
AN4351
Contents
1
2
3
2/10
Handling precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2
Mounting conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3
Silver filled conductive glue properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4
Glue attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5
Electrostatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.6
Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.7
Important . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Glue dispensing guidelines and recommended practice . . . . . . . . . . . 5
2.1
Storage and use of silver filled conductive glue . . . . . . . . . . . . . . . . . . . . . 5
2.2
Receiving inspection and preparation for use . . . . . . . . . . . . . . . . . . . . . . 5
2.3
Preparation of dispensing equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.1
Input parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.2
Relation between Time Pressure and deposit quantity . . . . . . . . . . . . . . 6
2.3.3
Needle choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.4
For semi-automatic mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3.5
For automatic mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
DocID025184 Rev 1
AN4351
Handling precautions
1
Handling precautions
1.1
Temperature
The maximum operating temperature of the EnFilm™ is 60 °C. Standard board mounting
techniques (example: high temperature soldering) are not compatible with these products
and should not be used.
1.2
1.3
1.4
Mounting conditions
1.
Due to its light weight, the EnFilm™ can easily slide out of its initial position during the
mounting process. It is recommended to apply a weight on the EnFilm™ to hold it down
during mounting and curing (around 20 g on each EnFilm™).
2.
If possible (depending on PCB design and the number of layers), it is recommended to
embed the EnFilm™ in the printed circuit board and substrate to avoid movement of
the EnFilm™ during glue curing.
3.
For small Engineering runs, a light and removable adhesive tape can be used to hold
down the EnFilm™ during mounting and curing - a ‘post it® note’ adhesive type will
work fine and can easily be removed after glue curing.
Silver filled conductive glue properties
1.
A silver filled glue has good adhesion properties on various different substrates.
2.
Uncured and non-polymerized silver filled glue will have weak adhesion strength
between the substrate and the EnFilm™.
3.
Unlike normal solder paste, no shrinkage phenomenon occurs during the curing of
silver filled glues.
Glue attachment
The EnFilm™ has to be attached on the substrate with at least one dot of conductive glue
on each pad.
To enhance component adhesion and mechanical stability additional dots on two other
corners can be done.
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Handling precautions
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Figure 1. Multiple dots
Dots
1.5
Electrostatic
Depending on the working environment and the type of support used, the dispensing quality
of the glue can be affected by the presence of static electricity to the extent of generating
glue splatters. It is recommended to take precautions to dissipate the static charges in order
to prevent these glue splatters which can result to potential short circuits. The risk of
generating glue splatters increases when the glue has been installed in a machine for
several hours in an uncontrolled environment due to the formation of tails in the dispensing
needle.
1.6
Preparation
Prepare the board contact surfaces by cleaning with Iso Propyl Alcohol (IPA) before
mounting the EnFilm™.
1.7
Important
It is mandatory to avoid short-circuiting the pads of the EnFilm™ at any time.
Thus, the EnFilm™ contacts must not be placed on the same conductive surface.
Respect the polarities of the connections: EnFilm™ interconnection positive (+) pad with
printed circuit board (PCB) positive (+) pad.
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Glue dispensing guidelines and recommended practice
2
Glue dispensing guidelines and recommended
practice
2.1
Storage and use of silver filled conductive glue
•
The silver filled glues are perishable material and needs to be stored with care. The
shipping container must be designed to protect the material in transit for up to 2 days.
Use carbon ice to store the material at minus 40 °C (or other temperature versus TDS
supplier).
•
Immediately upon receipt, unpack the shipping container and freeze the material at
minus 40 °C (or other temperature versus TDS supplier). Syringes containing silver
filled glues must be stored vertically with their caps on.
•
Glue shelf life at minus 40 °C depends on the glue material; please check the shelf life
information with the supplier.
•
It is not recommend to refreeze used material and to redistribute or repack glues pack
in syringes because syringes are packaged by special techniques to ensure no air
bubbles are trapped inside the syringe; it is instead recommend to choose smaller
syringe size like 5 cc or 3 cc.
For equipment set up purposes (and some engineering runs), thawed materials staying at
room temperature of less than 4 hours (including thawing time) can be refrozen 3 times
maximum. This refrozen material must not be used for production runs due to potential
reliability and quality risk (mechanical and electrical contact reliability can be downgraded).
For production runs, silver filled conductive glues can usually be used during 2 hours
without the need of adjusting and correcting input parameters (pressure, time). Beyond 2
hours, it is recommended to check and adjust input parameters to assure the same
dispensing quantity.
2.2
Receiving inspection and preparation for use
Silver conductive glues should be removed from cold storage and thawed at room
temperature.
Immediately, do not remove back end cap from the syringe, remove front end cap and install
needle according to Table 1.
The required thawing time will be dependent upon the syringe size; a good indication that
the material is ready is when condensation on the syringe disappears. Typical time is from
30 minutes to 1 hour for 5 cc syringe size. Thawing must be done with the syringes standing
vertically.
Never use heat to accelerate the thawing. Do not place syringes near any heat source
(ovens, furnaces) or immerse in hot and warm water. These practices will adversely affect
performance.
Syringes should be inspected prior to use; any evidence of separation (material, plunger),
large air voids or discoloration or dark aspect are indications of thermal excursions
rendering the syringe unfit for use.
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AN4351
After the syringe has reached ambient room temperature, it is ready for use:
•
Remove the back end cap from the syringe.
For setting up the dispensing quantity of a dispenser, it is recommended to use a scale (0.1
mg) function rather than using the time function of the time-pressure dispenser.
Due to the very small deposited quantity, it is necessary first to weigh a minimum of 30 dots
to calculate the weight average. This value must be kept in reference.
Various silver filled conductive adhesive have been evaluated, please find here below the
main dispensing parameters used (refer to Table 1).
Table 1. Input parameters
Gauge
Inside
diameter
Inch
25
0.010
Color
Length
code
Pressure
(Bars)
Total
weight 30
deposits
Weight
average
150 to 300
2
4.1 mg
0.14 mg
QMI 516 IE Henkel
600 to 800
1
2.2 mg
0.07 mg
PU 1000 Polytec
160
2
4.1 mg
0.14 mg
ACE 40810 Protavic
mm
0.25
Red
6.35
2.3
Preparation of dispensing equipment
2.3.1
Input parameters
2.3.2
Silver filled
conductive
adhesive
Dispense
time (ms)
•
Pressure
•
Dispense time in milliseconds: ms.
•
Internal diameter of needle
Relation between time pressure and deposit quantity
A high pressure with a short time increases flow (debit), whereas low pressure during a long
time increases precision.
The adjustment of the pressure should always be done in an increasing step. If a lower
pressure is needed, it must be reduced well below the desired pressure and then increased
to the desired level.
2.3.3
Needle choice
It is recommended using 6.3 mm needle length instead of a 12.7 mm needle length. It is not
recommended using conic needles due to the low viscosity of glue materials.
2.3.4
For semi-automatic mode
Manual operation with time pressure dispenser:
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•
The needle must be inclined at an angle between 45° to 80°.
•
The needle must be in contact with the surface during dispensing.
•
Do not move the needle while releasing the glue.
•
Lift up the needle perpendicularly after dispensing the glue.
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Glue dispensing guidelines and recommended practice
Figure 2. Step1: Contact
Figure 3. Step2: Dispense
Figure 4. Step3: Set back
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Figure 5. EnFilm deposit
2.3.5
For automatic mode
If needle is positioned vertically, a stand-off value between 0.05 to 0.2 mm with a typical
value of 0.15 mm is recommended.
Figure 6. Automatic dispense valve
Stand-off: 0.15 mm
Table 2. Recommended material (adhesive) for low temperature interconnection and
thermal profiles
Supplier
Reference
Temperature
Time
Henkel
QMI 516 IE
60 °C
90 mn
Polytec
PU 1000
25 °C
60 mn
Protavic
ACE 40810
60 °C
900 mn
Figure 7. Footprint
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5.46
45 °C
25.4
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3
Revision history
Revision history
Table 3. Document revision history
Date
Revision
27-Sep-2013
1
Changes
Initial release.
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AN4351
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