IPC-7526-2007 模板和误印板清洗指南.pdf - 第22页

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ solder cleaning process step be reviewed with local POTW of f icials before commencing the discharge of wastewater . Such a review may result in the POTW waiving the need for a permit, or in reducing the mo…

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

damage and spray ‘‘shadowing.’’ In addition, the design

must allow for easy loading and unloading of the PCAs

onto the board holder.

9.4 Compatibility Constraints with Cleaning Solutions

Care needs to be taken in the selection of cleaning equip-

ment and chemistries. The very narrow solid areas between

apertures on ﬁne pitch parts could be damaged due to

excessive pressure settings for the wash solution. Addition-

ally, if bristle brushes are used to abrade the residual mate-

rial in apertures the same situation could occur.

Excessive heat in the equipment could cause minor distor-

tion to the stencil resulting in misprints—due to the differ-

ent rates of expansion of the stainless steel foil, polyester

border, and aluminum frame. The epoxy bond could also

come under stress due to heat.

Depending on the cleaning chemistries chosen, there could

be a failure in the ﬁducials on the stencils. Fiducial ﬁllers

that are not compatible with cleaning chemistries or tem-

perature settings on equipment could release leaving no

method for alignment of the stencil to the boards.

10 ENVIRONMENTAL

Assemblers must consider the effect of the cleaning agent

on air emission, wastewater discharge, and solid waste gen-

eration. Special authorization or permits for air, wastewater

and special handling of solid waste are very often the rule

in those nations that have no precise legal deﬁnition of

permitted discharges. The following are most often a con-

cern:

Air

• VOCs (volatile organic compounds)

• Ozone depleting substances

• Global warming substances

• Odors

Wastewater

• Heavy metal cations (notably lead, tin and copper)

• Anions (notably phosphates, nitrites and sulfates)

• Complexing/chelating agents (notably EDTA salts and

ammonium/amine compounds

• PH (acid or base condition)

• COD/BOD

• Toxicity to aqueous life before and after biodegradation

• Other (temperature, solid matter, suspended matter, sur-

face tension modiﬁers, etc.)

Solid Waste

• Heavy metal cations (notably lead, tin and copper)

• All leachable toxic materials up to 100 years in autho-

rized discharge conditions

• Used solvent

10.1 Air Emissions Air emissions are a concern for some

chemical-cleaning agents used for stencil cleaning opera-

tions. Generally, there are two types of air emissions from

such a cleaning process; (1) VOCs and (2) water vapor.

VOCs are generated from cleaning with organic solvents

and aqueous cleaners that contain organic solvents. In cer-

tain nations and regions, VOCs are highly regulated

because their vapors react with nitrogen oxides (photo-

chemically) producing smog. The water vapor from an

evaporator that is used to concentrate the chemicals from a

wash tank may require an air emission discharge permit. In

any case, it is important to consult with the regulatory

agencies before a cleaning process is installed. Depending

on the particular chemical(s) emitted, the amount of the

chemical(s) emitted and the amount of other chemical

emissions from that facility, the emissions may or may not

be regulated by the State (other regional permitting author-

ity under the Clean Air Act). An air emissions permit may

be needed if the emissions thresholds for a given chemical

or a group of chemicals at that facility is exceeded. The

worldwide trend is toward increasing the stringency of

VOC regulations. However, the deﬁnition of what consti-

tutes a VOC varies much from one country or region to

another.

Odors in the workspace and/or odors exhausted to the out-

doors are often a primary concern to maintaining a good

working environment.

10.2 Wastewater The discharge of any wastewater

stream, both by total ﬂow and by chemical make-up must

conform to national, regional and local regulations in all

nations. These may vary from lax to very strict limits with

little ﬂexible conditions. Many nations, particularly in

Europe, have draconian legal requirements dictated on a

national scale, covering many aspects of wastewater qual-

ity. Others have less comprehensive regulations, covering

only the more important considerations. Local authorities

may offer derogations to national legislation where their

local treatment plant is able to handle the otherwise out-of-

tolerance waste. Derogations are frequently accorded to

small users, particularly if it may be shown that the cost of

treating a small quantity of slightly polluting waste would

be out of all proportion to the damage that could be caused.

It must be noted that because an installation is approved in

one place, it may not be elsewhere. In all cases, it is wise

to discuss an installation with the local authorities before

putting it into service, as a polluting fait accompli is never

looked at with a kindly eye.

In the USA, the discharge of the wastewater stream, both

by total ﬂow and by chemical make-up will very likely

require a permit form the local public owned treatment

works (POTW) under the Clean Water Act (CWA). In addi-

tion, such a permit may also require co-current approval

(and in rare cases, regional EPA approval). It is important

that any new or additional wastewater ﬂow from a post

February 2007 IPC-7526

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

solder cleaning process step be reviewed with local POTW

officials before commencing the discharge of wastewater.

Such a review may result in the POTW waiving the need

for a permit, or in reducing the monitoring requirements of

a required permit. Superfund regulations place liability on

all drain uses if contaminated sewer sites cannot be linked

to the generator. If using the drain for ﬁltered wastewater

discharge, the user could be held liable for a neighbor’s

problem and be required to share in the clean-up costs.

Even though there is no universal US EPA rule for elec-

tronics part cleaning, any state can have its own regulations

for these processes. Throughout the USA, these vary

greatly from one regulatory agency to another, from mini-

mal to very strict. Regulatory personnel’s interpretation and

knowledge of this process will determine the difficulty that

one will have with discharging the wastewater. Some local

communities may decide to prohibit a discharge of indus-

trial wastewater. Other communities will follow the state’s

requirements and will rely on the state to monitor the

wastewater for them.

In the past, many nations and regions (states) allowed com-

bining of domestic sewage with industrial wastewater

including heavy metals as long as the ﬁnal wastewater

complied with the regulations. However, today many of

these cleaning operations are now considered as a point

source discharge. With increasing frequency, regulatory

personnel are taking samples of wastewater from the wash

tank drain and the rinse water drain of the cleaning equip-

ment.

In most European countries and many Asian ones, it is a

legal requirement that the discharge be measured directly

from the machine or the individual wastewater treatment

plant and that dilution of the wastewater stream either from

within the machine or without it, is expressively forbidden.

In other words, if the discharge from the machine does not

conform to the regulations, the water must be puriﬁed in

such a way that it does.

One of the more difficult aspects of wastewater treatment is

that of heavy metal cations. Taking the three most impor-

tant ones for electronics cleaning, the known regulations at

the time of this writing may vary from place to place as

follows:

In some nations, the permitted concentration is expressed

in peak milligrams-per-liter, in other, parts-per-million. For

the sake of simplicity, the two units were considered here

as equivalent. Very few regulations in the world permit

integrating/averaging to determine the limit.

In the calculation of this average, those nations with unlim-

ited permitted total in cation concentration were ignored:

this ﬁgure is therefore an average of those nations with a

ﬁnite limit.

It is evident that removing heavy metals from wastewater

does not destroy these metals. At the best, they are trans-

ported into another form, such as concentrate from mem-

brane treatment or regenerated two bed ion exchangers, as

residues from mixed bed ion exchangers or as a solid pre-

cipitate after hydroxide or ferrite treatment. All these waste

materials are at least as dangerous as the original cations in

the wastewater. They are only displaced. It is a bounden

duty to ensure they are disposed of in as environmentally

friendly manner as possible, no matter the chosen way.

10.3 Solid Waste The disposal of spent or waste-

cleaning chemicals is regulated in most countries as haz-

ardous waste. Spent cleaning chemistries, ﬁlter cartridges,

activated carbon or others must be analyzed and character-

ized by someone knowledgeable in hazardous waste gen-

eration, storage and shipment regulations. In the USA, the

federal TCLP (Toxic Characteristic Leachate Procedure)

test is the minimum that must be performed. Applicability

of the hazardous waste rules subject a facility to extensive

regulations on personnel training, storage and handling

requirements and record keeping. Even if hazardous waste

rules are not applicable, local or state rules on solid waste

may apply. Some states offer technical assistance to aid in

this determination. Documentation of test results and

records must be kept to assure the regulatory agency of

compliance with today’s ‘‘cradle to grave’’ requirement.

Complete records of the amount of regulated wastes gener-

ated, transported, and disposed are required.

In addition to analogue regulations, there are very severe

rules in Europe simply for the transport of hazardous waste

and, for that matter, any toxic material. Furthermore, most

regions operate licensed liquid and solid chemical disposal

sites, which are specially constructed to protect the air, sur-

face and ground waters (especially phreatic sites) and the

surrounding soil. Every load of waste must be clearly

labeled as to the nature of the contents. Generally, it is a

wise precaution to make sure that a site can accept a given

waste before despatching it. Combustible waste is usually

incinerated in special kilns. In particular, special licenses

are required to transport waste across a national frontier,

according to the Basel Convention.

IPC-7526 February 2007

标准分享网 www.bzfxw.com 免费下载

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ

APPENDIX A

Terms and Definitions

Absorbed Contaminant: A contaminant attracted to the

surface of a material that is held captive in the form of a

gas, vapor or condensate.

Adhesive: A substance such as glue or cement used to

fasten objects together. In surface mounting, an epoxy

adhesive is used to adhere SMDs to the substrate.

Adhesive Printing: Stencil printing no longer is limited to

the deposition of solder paste. Stencils may be used to

deposit adhesives on mixed-technology PCA designs in

which the bottom of the board features parts attached with

adhesives for wave soldering.

Aliphatic Solvent: ‘‘Straight chain’’ solvents, derived

from petroleum, of low solvent power.

Alkaline Cleaner: An aqueous engineered composition

that contains alkaline salts. These materials are in a pH

range of 7-14.

Ambient: The surrounding environment coming into con-

tact with the system or component in question. Typically

refers to room temperature processing.

Aperture (Stencil): Openings in the stencil through which

solder paste or adhesive is deposited onto the circuit board.

Aqueous Flux: Water-soluble organic ﬂux.

Aspect Ratio: Aperture width to depth ratio. If the wall

area exceeds the land area, the surface tension of the sol-

der paste will be such that more of the paste will adhere to

the wall, risking a clogging condition.

Azeotropic Cleaning Mixture: A liquid mixture of two or

more solvents that behave like a single solvent. The vapor

pressure by partial evaporation of the liquid has the same

composition as the liquid cleaning chemistry.

Bare Board: An unassembled (unpopulated) printed cir-

cuit board.

Base Solderability: The ease with which a metal or metal

alloy can be wetted by molten solder under minimum real-

istic conditions.

Batch Cleaning Process: The cleaning of multiple parts

or ‘‘batches of parts’’ as a group where process cycle times

are controlled.

BOD: Biological oxygen demand.

Bridging, Electrical: The unintentional formation of a

conductive path between conductors.

B-Side: The bottom side of a printed circuit assembly.

COD: Chemical oxygen demand.

Cold Hand Cleaning: Manual cleaning using a presatu-

rated wipe or brush that contains a cleaning chemistry that

readily evaporates.

Corrosion: The attack of cleaning chemistry, ﬂuxes, and

ﬂux residues on base metals.

Degradation: A decrease in the performance characteris-

tics or service life of the cleaning chemistry.

Dewetting: A condition that results when molten solder

coats a surface and then recedes to leave irregularly shaped

mounds of solder that are separated by areas that are cov-

ered with a thin ﬁlm of solder and with the basis metal not

exposed.

Double-Sided Printed Board: A printed board with a

conductive pattern on both of its sides.

Emulsion Cleaning: An aqueous cleaning mixture that

holds immiscible soils, such as adhesive, in suspension.

Feature: The general term that is applied to a physical

portion of a part, such as a surface, hole or slot.

Fine-Pitch Technology: A surface mount assembly tech-

nology with component terminations on less than 0.625mm

(0.025-inch) centers.

Flux: A chemically and physically active compound that,

when heated, promotes the wetting of a base metal surface

by molten solder by removing minor surface oxidation and

other surface ﬁlms and by protecting the surfaces from

reoxidation during a soldering process.

Flux Activity: The degree or efficiency with which a ﬂux

promotes wetting of a surface with molten solder.

Flux Residue: A ﬂux-related contaminant that is present

on or near the surface of a solder connection.

Hydrophilic: Water loving or having a strong affinity for

water.

Hydrophobic: Water hating or having a strong aversion to

water.

Hydroscopic: Water loving or having a strong affinity to

water.

In-line Cleaning: Parts are processed continuously on a

conveyor with process cycle time being controlled by the

conveyor speed.

Ionic Cleanliness: The degree of surface cleanliness as

measured by the number of ions or weight of ionic matter

per unit square of surface.

Manual Cleaning: A cleaning step where parts are pro-

cessed manually with process cycle time controlled by

operator.

February 2007 IPC-7526