Soldering Techniques by sha19

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Program objective Basics of Soldering
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Solder, Flux, Wetting Action Solderability, Characteristics of Good Solder Joint Soldering Defects
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SOLDERING
SOLDERING IS THE PROCESS OF
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CONNECTING(BONDING) TWO METAL SURFACES TOGETHER TO FORM RELIABLE ELECTRICAL PATH.
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RELIABILITY - ?
VIBRATION
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CORROSION MECHANICAL SHOCK TEMPERATURE SPECIFIED PERIOD: >7<15Yrs.
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IMPORTANCE of Soldering
•MEDICAL EQUIPMENTS •MILITARY EQUIPMENTS •SPACE PROGRAMS •TELECOMMUNICATIONS •AVIONICS 20 – 30% EQUIPMENTS FAILED DUE TO DEFECTIVE SOLDER JOINTS !!
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DISTRIBUTION OF ENVIRONMENTALLY RELATED FIELD FAILURES
2% 40%

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27%

TEMPERATURE ALTITUDE VIBRATION SALT SAND & DUST

2% 4% 6% 19%

MOISTURE SHOCK

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Basic Principle of Soldering

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Flux

Solder

Heat

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Solder is a fillet material used to join the parent materials

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Solder Mixtures and Uses
• Mixture is expressed as percentage of lead, (Pb) and tin (Sn) and/or silver (Ag) • Increased lead content means higher melting point • Normal solder will not adhere to aluminum, stainless steel

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PURPOSE OF TIN LEAD ALLOY
GOOD MECHANICAL STRENGTH

QUICK SOLIDIFICATION Training GOOD WETTING POWER CTE MATCHES TO COPPER NON CORROSIVE
LOW RESISTIVITY

LOW MELTING TEMPERATURE

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Types of Solder
As per Use :
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Bar Solder -For Wave Soldering Solder Wire - For PCB & Connector wiring Solder Paste or Cream -For Vapour phase soldering
Solder Pellets : For Solderability test
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Types of Solder
As per Composition :
Alloy – TIN- LEAD Melting point

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Sn63 Pb37 Sn60 Pb40 Sn55 Pb45 Sn50 Pb50 Sn45 Pb55 Sn40 Pb60

1830C 1830 C - 1890 C 1830 C - 2030 C 1830 C - 2150 C 1830 C - 2260 C 1830 C - 2370 C

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1. 60Sn/40Pb

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183C Solid

189C Plastic Liquid

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2. 63Sn / 37Pb

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183C Solid Liquid

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Common Solder Wire Sizes

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/ N2

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Flux-What it Is and What it Does
• Flux is a blend of rosin and chemicals that remove oxides from the area to be soldered and assists in solder adhesion

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Flux Selection
• Trade-off between how aggressive a flux is at removing oxides vs. the need for post-solder flux cleaning (removal). • Post-solder corrosion can lead to long-term reliability problems.

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Long-term Reliability

FLUX ACTIVITY

Efficacy of Soldering

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The Ideal Flux
• Inactive at Room Temperature • Activates at slightly below the melting point of solder • Stable at soldering temperature

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Non - corrosive
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Non - conductive
Safe Easily cleanable Thermally stable
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ROSIN

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ORGANIC

ROSIN MILDLY ACTIVATED

ROSIN ACTIVATED

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IN-ORGANIC *ZINC AMMONIUM CHLORIDE ACTIVE COMPONENTS : ACIDS

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STEARIC, GLUTAMIC, LACTIC, CITRIC
HOLOGENS : HYDROCHLORIDES, BROMIDES, HYDRAZINE, Etc.

AMIDES & AMINES, UREA, TRIETHANOLAMINE OTHER FLUXES : WATER SOLUBLE FLUXES NO-CLEAN FLUXES

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This diagram shows why No-clean Flux-cored solder seldom works as well as RMA cored solder

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Large volume of flux in RMA solder wire core

Strong acid RMA Flux
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Smaller volume of flux in No clean solder wire core
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Weak acid

No Clean Flux
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A known weight of solder & flux are placed on a freshly cleaned copper sheet & floating on a molten solder a specified time the area solder spread determines property of the flux. Resistance corrosion is then assessed by placing the specimen into the humidity chamber at 40°C & 98% RH for duration of 500 Hrs. The presence of green-blue copper corrosion products indicate the corrosion behaviour of flux.
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Types of Irons
• Irons
– different sizes and wattages

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• Guns
– good, general use item

• Pencil-type
– ideal for close-in work

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Choose the Right Tool for the Job
• Many different sizes and styles of tips • Heat transfer is important • Solder should melt within several seconds • 30Watt iron is sufficient for most uses • The larger the tip and working surface, the faster heat transfer occurs • Increasing wattage does not necessarily increase tip temperature of iron

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Tip Plating

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Tip Care: Choosing a Tip
• Select the correct tip
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Choosing The Correct Iron
• Two Basic Rules of Thumb • Choose an iron tip temperature of at least 400 C more than the solder you are using • Use the largest tip that will fit into the area you are working on without damaging nearby components
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Connection (Not Tip) Temperature
• High enough to melt solder & form intermetallic. • High enough to activate flux & cause wetting. • Low enough to avoid damage to components and PCBs

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POOR WETTING

GOOD WETTING COMPONENT & PCB DAMAGE
INCREASING TEMPERATURE
GOOD HEAT TRANSFER

TOO LOW COLD SOLDER JOINT

TOO HIGH
EMBRITTLEMENT

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 DAMAGE TO PLASTIC PARTS

 LIFTING OF PADS
 OVERHEATED JOINTS

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 DAMAGE TO HEAT SENSITIVE COMPONENT  BURNT FLUX 80-120-350
 HEAVY OXIDATION ON BITS

 WASTAGE OF ELECTRICAL POWER

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Tip Temperature Ranges
(63/ 37, 60/40, and 62/36/2 tin/lead/silver)
Type of Work Thick and thin film microcircuits F 540  20 575  25 735  15 820  20 820  40 810  50 C 280  11 300  14 390  8 435  11 435  22 430  28

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Flexible printed circuits Fine copper wire Multilayer Printed Circuits* Standard Printed Circuits* Terminals and lugs*

*Subtract 100F (55C) for irons with fully controlled tip temperatures.

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Tinning your iron
• Tinning is the process of keeping a coating of melted solder on the working surface of the iron • Clean iron down to bare metal surface, immediately apply solder and melt all over surface, wipe away excess

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Tinning Your Iron
• This tip has not been tinned for some time and has oxidized, rendering it difficult to solder with

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ETHYL ALCOHOL

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Ex:

ISOPROPYL ALCOHOL TRICHLORO TRIFLORO ETHANE DE IONISED WATER
TRICHLORO ETHANE

PERCHLORO ETHANE TETRACHLO DI FLOURO ETHANE

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The Penetration of Atoms and Molecules of Solder and Copper into each other & formation of

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Intermetallic Layer

SOLDER

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COPPER

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SOLDER

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COPPER

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SOLDER

Oxides

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COPPER

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SOLDERABILITY
PROPERTY OF THE SURFACE WHICH ALLOW IT TO BE WETTED BY MOLTEN SOLDER
SOLDERABILITY OF METALS:

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TIN, GOLD, SILVER

: EXCELLENT

COPPER, BRASS, LEAD STEEL, ZINC, NICKEL ALUMINIUM & HIGH ALLOY STEEL CAST IRON CHROMIUM

: GOOD : FAIR : DIFFICULT : REQUIRES SOLDERABLE COATING

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SOLDERABILITY =
WETTABILITY OF THE SUBSTRATE BY MOLDEN SOLDER Training

GLOUBLE TEST

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• Wetting refers to the interaction of a liquid with a “dry” surface • The wettability of two materials can be measured in terms of the wetting angle (also called dihedral or contact angle).  AB  AC
A B A C

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 AB   AC
Hence, there is more wettability between A and C.

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Simple Solderability Testing for COMPONENT LEADS
SAMPLE TEST : COMPONENT LEAD : FLUX FOR 1 MIN : SKIM : DIP VERTICALLY INTO CLEAN SOLDER 4+1+1 SEC : CLEAN IN SOLVENT PERFECT WETTING SMOOTHER THAN ORIGINAL FREE FROM ALL DEFECTS : FAIL TO WET : ANY OTHER DEFECTS : TRY ANOTHER SAMPLE : AGAIN FAILS REJ LOT

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RESULT:

A/R

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Simple Solderability Testing for PCB (PTH)
SAMPLE : 2” x 2” IMMERSE IN FLUX 1 MIN FLOAT ON SOLDER 5 SEC
CLEAN ALL HOLES SHALL FILL WITH SOLDER

TEST METHOD : : RESULT
: :

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:
:

PADS (DOME OF SOLDER)
ABSENCE OF DEWETTING NONWETTING VOIDS ETC.

ACC/REJ

: :

2 ‘OR’ MORE PTH FAIL TO FILL 2 OR MORE COMPONENT PADS
FAIL TO WET 2 OR MORE VOIDS

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non-wetting of plain laminate

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Dewetting of plain laminate:

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SOLDERABILITY
KEY TO SUCCESS : THE 70% PROBLEM
5% 5% 5%

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15% 50%

SOLDERABILITY OF BOARDS SOLDERABILITY OF COMPONENTS HANDLING AND ASSEMBLY DESIGN DEFECT SOLDER MACHINE OTHERS

20%

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Solderability
Depends on

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– Surface cleanliness (Fluxing)

Control through
– Incoming Inspection – Storage – Handling – Oxidation

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SOLDERABILITY STANDARDS
ANSI / IPC - S - 804 DIN 32506
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MIL - STD - 202 BS 2011 JSS 50101 IS 9001 Part (18)
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Characteristics of a Perfect Joints
P1 P2 CLEAN SMOOTH
BRIGHT

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P3

P4
P5

CONCAVE
LEAD VISIBLE

P6
P7

COMPLETE WETTING
THIN EDGES

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Perfect joints

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GOOD JOINT

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CAVITY

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COSMETIC APPEARANCE BUT DEFECTIVE

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Solder Feathers out to a thin edge
Lead

Concave Fillet

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Cross section view of A round Lead on a flat surface
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SOLDER COATING COPPER COATING

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EPOXY

A PERFECT PTH

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Summary
• Soldering is the bonding of metallic surfaces via an intermetallic alloy.
Training – The Intermetallic bond is created by a diffusion process.

• Soldering is an interaction between heat delivery, flux chemistry, and solder chemistry.

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The Soldering Process
• The solder wire and the heated tip are applied to the lead and pad • The connection is brought to 40C above the melting point of solder
– the flux becomes active

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• Solder flows
– it moves across the surface, wicks up the lead, and fills the through-hole/covers the pad

• The heated tip is removed
– the solder solidifies

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Clean the bit
Heat up the joint

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Insert component

Good Soldering Process...

Apply solder from opposite side

Cut the leads

Remove Iron gently

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DEFECTS
NON-WETTING DEWETTING DELAMINATION PIN HOLES/BLOW HOLES OVER HEATED JOINT EXCESS SOLDER INSUFFICIENT SOLDER BRIDGING ICICLES WRONG MOUNTINGS MISALIGNMENTS REVERSE POLARITY

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Poor Lead Solderability

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Poor Wetting
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Poor Wetting
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Dewetted land, partially wetted spade termiantion

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Good wetting of vertical terminations, poor wetting of plated through holes

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65 per cent fillet

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90 per cent fillet

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Cracked Joint

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Lifted Component
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Incomplete solder joint
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Amount of solder in the joint

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Defective

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Acceptable

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Acceptable

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Acceptable

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Defective

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Bridging between adjacent vertical square wire terminations

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Blowhole in solder fillet

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Solder Flags

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TOO QUICK TOO MUCH SOLDER FLICKING

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STROKING PRESSING RELUCTANCE TO CHANGE BIT DRY SPONGE MESS OF TOOLS SOLDER SPLASH RELUCTANCE TO CHANGE
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ESD Susceptibility Symbol

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DO’S
       MINIMISE HANDLING. KEEP PARTS IN ORIGINAL PACKING UNTILL READY FOR USE. USE ESD PROTECTIVE CONTAINERS AND BAGS. DISCHARGE STATIC BEFORE HANDLING TOUCHING NEARBY GROUNDED SURFACE. HANDLE DEVICES BY THE BODY. TOUCH THE ESD PROTECTIVE TOUCHING INSIDE OF DEVICE. KEEPA DUST FREE WORK AREA. PACKAGE BEFORE DEVICE BY

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Summary Here's a summary of how to make the perfect solder joint:
All parts must be clean and free from dirt and grease. Try to secure the work firmly. "Tin" the iron tip with a small amount of solder. Do this immediately, with new tips being used for the first time.

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Clean the tip of the hot soldering iron on a damp sponge (many people then add a tiny amount of fresh solder to the cleansed tip). Heat all parts of the joint with the iron for under a second or so.
Continue heating, then apply sufficient solder only, to form an adequate joint.

Remove and return the iron safely to its stand. It only takes two or three seconds at most, to solder the average PCB joint.

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Do not move parts until the solder has cooled.

DONT’S
 TOUCH THE LEADS OF DEVICE.

 SLIDE ES DEVICES OVER ANY SURFACE.

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 PUT MASKING TAPE ON PROGRAMMABLE IC’s.
 STORE OR CARRY SENSITIVE COMPONENTS OR ASSEMBLIES IN PLASTIC BAGS.

 STORE SENSITIVE COMPONENTS IN THERMOCOLE/PLASTIC FOAM.  HANDLE ES DEVICES IN “NON ESD CONTROLLED” ENVIRONMENT.

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