IPC-D-279 EN.pdf - 第113页

APPENDIX I Solvents I-1.0 INTRODUCTION Surface Mount Printed W iring Assemblies (PW A) are sub- jected to solvents (including water) and chemicals during manufacture, rework, repair and service. These agents include thos…

Silicon Controlled Rectiﬁer (SCR) with I

< 0.175 A at

100°C ambient temperature

Precision Voltage Regulator Diodes: Line or Load Voltage

Regulation < 0.5%

Microwave Devices (Schottky barrier diodes, point contact

diodes, and other detector diodes), Frequency > 1 giga-

Hertz

Thin-Film Resistors

Thick-Film Resistors where the ESD ﬁeld across the ﬁlm >

2 kV/mm

Hybrids utilizing Class 1 parts

H-2.4 CLASS 2: Sensitivity Range 2,000 to 3,999 Volts

Devices or Microcircuits when identiﬁed by Appendix A

Test Data as Class 2

Metal Oxide Semiconductor (MOS) devices, discrete

Integrated Circuits (IC)

Very High Speed Integrated Circuits (VHSIC)

Operational Ampliﬁers (OP AMP)

Junction Field Effect Transistor (JFET)

Precision Resistor Networks (Type RZ)

Hybrids utilizing Class 2 parts

Low Power Bipolar Transistors, P

< 100 mW with IC <

100 mA

H-2.5 CLASS 3: Sensitivity Range 4,000 to 15,999 Volts

Devices or Microcircuits when identiﬁed by Appendix A

Test Data as Class 3

Metal Oxide Semiconductor (MOS) devices, discrete

Integrated Circuits (IC)

Very High Speed Integrated Circuits (VHSIC)

Operational Ampliﬁers (OP AMP)

Junction Field Effect Transistors (JFET)

Small Signal Diodes with power < 1 watt or IO < 1

Ampere

General Purpose Silicon Rectiﬁer Diodes

Silicon Controlled Rectiﬁer (SCR) with IO > 0.175 A at

100°C ambient temperature.

Low Power Bipolar Transistors with 350 mW<P/T/<100

mW and 400 mA>I/C/ >100 mA

Optoelectronic Devices (LEDs, Phototransistors, optocou-

plers)

Resistor Chips

Piezoelectric Crystals

Hybrids utilizing Class 3 parts

H-2.6 CLASS ‘‘4’’: Sensitivity Range 16,000 Volts

CONSIDERED NON-ESD SENSITIVE.

The above values are considered ‘‘default’’ values for the

part type; where vendor and part speciﬁc data exists and

where the database structure permits vendor speciﬁc data,

that data is to override the default value.

July 1996 IPC-D-279

101

APPENDIX I

Solvents

I-1.0 INTRODUCTION

Surface Mount Printed Wiring Assemblies (PWA) are sub-

jected to solvents (including water) and chemicals during

manufacture, rework, repair and service. These agents

include those used in soldering (alcohols, glycols and other

solvents in ﬂux vehicles at temperatures approaching

150°C), in cleaning the assembly after solder (saponiﬁers,

neutralizers, hot water, terpene, chloroﬂuorocarbon (CFC)

mixtures, hydrochloroﬂuorocarbon (HCFC) mixtures and

other halogenated solvents and blends at moderate process

temperatures, during removal of conformal coatings with

various chemicals, and during service (hydraulic and cool-

ing ﬂuids and fuels in military applications; alcohols and

halogenated hydrocarbons during cleanup). These solvents

and chemicals can adversely affect the solder mask (SM),

printed wiring board (printed board), conformal coating

(CC), printed board or component legends and markings as

well as degrade thin or mechanically stressed sections of

plastic components. Section 7 of Electronic Materials

Handbook, Volume 1, Packaging, 1989, discusses the vari-

ous conformal coating (CC) chemistries. Where the adhe-

sion of the CC, solder mask (SM) or marking to the under-

lying layer has been weakened (as evidenced by swelling

or wrinkling), abrasion or high velocity water or high

velocity solvent may lift the overlying material. Where the

intimate adhesion of the CC to the SM or printed board

laminate is disturbed between traces which are DC biased,

electrochemical corrosion and dendriting may occur under

moist environment conditions. See IPC-TR-476, IPC-SM-

840, and IPC-CC-830 for discussion on dendrites, solder

masks and conformal coating compatibilities. See also the

section in these guidelines on various other solder mask

and conformal coating issues.

Solvents under pressure, including water, can mechanically

remove or chemically dissolve lubricants needed for the

proper operation of switches, potentiometers and other

moving components.

During servicing, alcohols and halogenated hydrocarbons

may be applied to the PWA during cleanup. The PWA may

be exposed to hydraulic ﬂuids and fuels in military appli-

cations.

The D-limonene (terpene) based solvents have question-

able compatibility with, or are not recommended for, short

term contact at room temperatures with rubbers of nitrile,

ethylene-propylene, butyl, natural, neoprene or silicone

(which swells); plastics (and their alloys and blends) such

as polystyrenes (PS), polycarbonates (PC), polysulfones,

polyvinyl chloride (PVC), polyallomer, polyurethane

(PUR), ABS, low density polyethylene (LDPE), and poly-

vinylidene ﬂuoride (PVDF); nor with metals such as cop-

per and brass. D-limonene solvent can also weaken the

adhesion of printed board marking; this effect may be of

signiﬁcance when high velocity water and solvent washes

and rinses are employed. If D-limonene is trapped under

low clearance components, resulting in prolonged expo-

sure, softening of the conformal coating or solder mask and

degradation of the component plastic may occur. A general

rule of thumb is that a material which survives CFC and

chlorinated solvent cleaning and is water resistant should

be compatible with D-limonene.

The common halogenated cleaning solvents decompose at

high temperatures or in the presence of catalytic metal sur-

faces. Extremely high halide levels have been found in

droplets of water ﬂoating on the solvent surface in the cold

sump of vapor degreasing systems; in these cases, the

water absorbing cartridge had failed or the solvent stabili-

zation additives were exhausted. The halides deposit onto

assemblies which are ‘‘cleaned’’ in the cold sump. These

halogenated solvents can diffuse through the rubber seal of

aluminum electrolytic capacitors; the result is the dissocia-

tion of the solvent inside the component, the release of

HCl, the corrosion of the aluminum foil, and failure of the

capacitor. A solution is the use of capacitors where the

elastomeric seal is augmented by a hermetic, epoxy or

other polymer seal effective in greatly reducing the diffu-

sion rate of the solvent.

I-2.0 MATERIALS AFFECTED

Acrylate and epoxy solder mask materials should not be

exposed for long durations to solvents and solvent systems

containing methylene chloride, tetrahydrofuran, butyrolac-

tone, N-methyl 2 pyrrolidinone, d-limonene, ethylene gly-

col ether, propylene oxide glycol ether, methyl alcohol,

dimethylsulfoxide (DMSO) or dimethylformamide (DMF);

these are constituents of systems designed to remove con-

formal coatings based upon acrylate and epoxy chemistries.

DMF has been used as an electrolyte in aluminum electro-

lytic capacitors; its use has diminished because of its car-

cinogenic properties and its low ﬂash point. Butyrolactone

is used as an electrolyte in aluminum electrolytic capaci-

tors, replacing DMF. The susceptibility to solvents differs

between dry ﬁlm SM and liquid photoimageable SM mate-

rials and between epoxy and acrylate SM materials.

Conformal coating (CC) materials differ in their response

to solvents, depending upon their chemistry and curing

mechanisms. Some systems are cured by heat or drying

such as epoxy, acrylate, polyurethane, silicone, and ﬂuo-

ropolymer. Other CC materials are cured by ultraviolet

(UV) light and are based upon resin systems such as epoxy,

IPC-D-279 July 1996

102

acrylated urethane, acrylated epoxy urethane, epoxidized or

acrylated silicone. Poly (para-xylylene) or Parylene

is a

unique in-situ polymerized material.

During CC removal prior to PWA rework, extreme atten-

tion must be paid to conﬁning the solvent attack to the

conformal coating; the interface between the SM and CC

can be preferentially attacked. SM-CC interfacial voids

may result in interconductor dendrites under DC bias and

moist environment service conditions. The volume under

low clearance components must be cleared of these sol-

vents to minimize attack of the SM; vigorous DI water

washing and thorough drying is required, particularly

where acidic or basic ‘‘activators’’ are present in the sol-

vent blend.

Activator residues may result in PWA failures due to cor-

rosion and dendrites. Residual solvents which are relatively

inert at room temperature may be detrimental at the high

temperatures of solder reﬂow.

Silicones are susceptible to chlorinated hydrocarbons,

alkanes and aromatics. Silicone gels are susceptible to

swelling by CFCs and HCFCs.

Fluoropolymer CC materials such as ﬂuoro (acrylate) and

ﬂuorinated terpolymers are susceptible to CFCs, HCFCs,

ketones, halogenated hydrocarbons, esters and aromatics.

Polycarbonates are susceptible to chlorinated hydrocar-

bons, ketones, and bases. Diallyl phthalate (DAP) may be

susceptible, at soldering temperatures, to formic or citric

acids found in some ﬂux systems.

Some phenolics, particularly those with organic ﬁller, are

susceptible to bases and ketones.

I-3.0 COMMON CLEANING SOLVENT FAMILIES

Ketones include acetone, methyl ethyl ketone, and methyl

isobutyl ketone.

Aromatics include benzene, toluene, gasoline, N-methyl

2-pyrollidinone, terpene (d-limonene), and some aircraft

ﬂuids such as hydraulic or fuel. Halogenated hydrocarbons

include CFC and CFC blends with methylene chloride,

methanol, ethanol; hydrochloroﬂuorocarbon (HCFC);

hydroﬂuorocarbon (HFC); and chlorinated hydrocarbons

(methylene chloride, trichloroethane, trichloroethylene, and

methyl chloroform).

Bases include ammonia, amines, neutralizers and saponiﬁ-

ers.

Alcohols (organic bases) include methyl, ethyl, propyl, and

butyl alcohols.

Esters (organic salts) include butyl acetate and ethyl

acetate.

I-4.0 HCFC BLEND AND OTHER DATA

Plastic Solvent Compatibility (Boiling liquid, 5 minutes)

HCFC Blend HCFC 141b/HCFC 123/ 2.5% Methyl

Alcohol/ 0.3% Stabilizer

Incompatible: Acrylonitrile Butadiene Styrene (ABS),

Acrylics, Cellulosics, Polycarbonate (PC), Polystyrene,

Butyl Rubber Adhesive

Probably incompatible: Polyphenylene Oxide (PPO)

CFC-113 + Methyl Alcohol

Incompatible: Cellulosics

Probably incompatible: Polystyrene

Data primarily for the equipment designer, Long Dura-

tion Exposure

Plastic-Solvent Compatibility (Liquid at 50°C, 24 hours)

might be speciﬁed but no extrapolation is possible to con-

ditions such as 100°C or Boiling Point, 1 minute (cleaning)

or 25°C, 24 hours (trapped between a component and

printed board).

Dupont Hydrocarbon Solvent (Axarel)

Incompatible: Cellulosics, Polyacrylate, Polycarbonate

(PC), Polystyrene

Probably incompatible: Acrylonitrile Butadiene Styrene

(ABS), Acrylics, Ionomer, Polyphenylene Oxide (PPO),

Polypropylene, Polyvinyl Chloride (PVC), Chlorinated

Polyvinyl Chloride (CPVC).

Solder mask or conformal coating may be affected if the

solvent is trapped under low clearance components.

Elastomer-Solvent Compatibility (Extractables, boiling, 8

hours)

HCFC Blend HCFC 141b/HCFC 123/ 2.5% Methyl

Alcohol/ 0.3% Stabilizer

< 1%: Fluoroelastomer (Viton B), Perﬂuoroelastomer

(Kalrez)

< 5%: Polyurethane, Chlorosulfonated Polyethylene,

Polyester TPE, Polysiloxane (Silicones), Polysul-

ﬁde FA/ST, Fluoroelastomer (Viton A)

< 10%: Isobutylene-isoprene, Natural Polyisoprene

> 10%: Acrylonitrile Butadiene, Styrene-Butadiene, Poly-

chloroprene, Ethylene/Propylene Terpolymer

CFC-113 + Methyl Alcohol

< 5%: Polyurethane, Isobutylene-isoprene, Polyester

TPE, Natural Polyisoprene, Polysiloxane (Sili-

cones), Polysulﬁde, Fluoroelastomer (Viton A)

< 10%: Styrene-Butadiene, Polychloroprene,

> 10%: Acrylonitrile Butadiene, Ethylene/ Propylene Ter-

polymer

Elastomer Solvent Compatibility (% Weight Change, Liq-

uid, 50°C, 168 hours) (For most of these materials, % Lin-

ear Swell is approximately

⁄

the % Weight Change).

Dupont Hydrocarbon Solvent (Axarel)

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