IPC-7526-2007 模板和误印板清洗指南.pdf - 第9页

ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Figure 1-6 Bridging or Poorly Deﬁned Solder Paste Printing (Figur e 1-6) Damage to the stencil patterns during removal of excessive solder paste or in a cleaning process will result in poorly deﬁned joints …

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Figure 1-2 Solder Paste Buildup on Walls of Stencil

Apertures

Figure 1-3 Solder Paste Buildup on Walls of Stencil

Apertures

(Figures 1-2, 3) Solder balls attach to the walls of the

stencil aperture over time. Failure to clean this buildup

from the stencil affects the amount of deposited solder

paste and could potentially cause open solder joints, bridg-

ing, and solder ball formation on the subsequent PCA.

Figure 1-4 Open or Insufficient Solder Joints

(Figure 1-4) When solder paste and/or the ﬂux vehicle is

not completely removed from stencil apertures in the clean-

ing operation the dried residue partially or completely

blocks the correct volume of solder paste, resulting in

insufficient or open solder connections.

Figure 1-5 Solder Balls Following Solder Reﬂow

(Figure 1-5) Water or solvent remaining on circuit boards

or stencils following cleaning may be mixed with the sol-

der paste resulting in satellite solder ball formation in the

solder reﬂow process. Improper cleaning of solder paste

from miprinted boards can leave large quantities of solder

balls from the solder paste on and around the lands and in

the vias.

IPC-7526 February 2007

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Figure 1-6 Bridging or Poorly Deﬁned Solder Paste

Printing

(Figure 1-6) Damage to the stencil patterns during

removal of excessive solder paste or in a cleaning process

will result in poorly deﬁned joints or bridged parts.

Improper rinsing of stencils can leave surface contaminants

or residual cleaning ﬂuid on the surface of the stencil.

These contaminants promote ﬂux bridging under the sten-

cil during the printing process. The release of the board

from the stencil creates a vacuum as the stencil separates

from the board, sucking the solder paste beneath the sten-

cil, leaving poorly deﬁned prints or bridges.

IPC-7526-1-7

Figure 1-7 Failure to Place the Stencil on a Level Plane

(Figure 1-7) The stencil must sit on a level plane that is ﬂat

with well-identiﬁed points and lines. The stencil should

contact the board at the solder mask height. Variations in

hot air solder leveling (HSAL) or excessive legend ink

thickness can lead to poor gasketing, which will allow sol-

der paste to ﬂow beyond the aperture opening on the bot-

tom of the stencil resulting in poor print deﬁnition.

Board Coplanarity

Stencil

Solder

Level

Board

Ledgend

Solder

Mask

Copper

Pad

FR4

Composite

Material

IPC-7526-1-8

Figure 1-8 Variations in Solder Mask Thickness

(Figure 1-8) Variations in solder mask thickness contribute

to inconsistencies in solder paste deposition. This condition

is similar to the board coplanarity problem and will lead to

poor deﬁnition and increase the need for stencil wiping.

Solder Mask Thickness

IPC-7526-1-9

Figure 1-9 Inconsistent Component Land Width

(Figure 1-9) Component land width must be consistent.

Variations contribute to inconsistencies in solder paste

deposition. If the land is smaller than the aperture, paste

will ﬂow beyond the land and if soldermask is not present,

the possibility of bridging between the lands will increase.

Solder Mask Thickness

IPC-7526-1-9

Figure 1-10 Misaligned Stencil

(Figure 1-10) Poor alignment contributes to inconsisten-

cies in solder paste deposition and increases contamination

of the stencil bottom. This leads to poor deﬁnition on sub-

sequent prints and increased frequency of the stencil bot-

tom cleaning to maintain acceptable print quality.

Alignment Accuracy

0.016˝ pitch

0.050˝ pitch

February 2007 IPC-7526

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2 BIBLIOGRAPHY OF DOCUMENTS, SPECIFICATIONS

AND REFERENCES

The following documents are provided as possible sources

of additional information.

2.1 IPC

IPC-SC-60 Post Solder Solvent Cleaning Handbook

IPC-SA-61 Post Solder Semiaqueous Cleaning Handbook

IPC-AC-62 Post Solder Aqueous Cleaning Handbook

IPC-CH-65 Guidelines for Cleaning of Printed Boards and

Assemblies

IPC-CA-82 General Requirements for Thermally Conduc-

tive Adhesives

IPC-A-610 Acceptability of Electronic Assemblies

IPC-3406 Guidelines for Electrically Conductive Surface

Mount Adhesives

IPC-3408 General Requirements for Anisotropically Con-

ductive Adhesive Films

IPC-7525 Stencil Design Guidelines

2.2 Joint Industry Standards

J-STD-001 Requirements for Soldered Electrical and Elec-

tronic Assemblies

J-STD-005 Requirements for Soldering Pastes

2.3 American Standards for Testing Materials

2.4 Federal Laws and Standards

CAA Clean Air Act

CWA Clean Water Act

CERCLA Comprehensive Environmental Response, Com-

pensation and Liability Act

RCRA Resource Conservation and Recovery Act

SARA Superfund Amendment and Reauthorization Act

2.5 Department of Defense

MIL-C-85447 Cleaning Compounds, Electrical & Elec-

tronic Components

2.6 Occupational Safety and Health Administration

OSHA 29 CFR 1910.106 Flammable and Combustible Liq-

uids

OSHA 29 CFR 1910.134 Respiratory Protection

OSHA 29 CFR 1910.1000 Air Contaminants

2.7 Environmental Protection Agency (EPA)

EPA 40 CRF 63 National Emission Standards for Hazard-

ous Air Pollutants for Source Categories

EPA 40 CFR 82 Protection of Stratospheric Ozone

EPA-453/R-94-081 Guidance Document for the Haloge-

nated Solvent Cleaner NESHAP

EPA 40 CFR 117. Determination of Reportable Quantities

for Hazardous Substances

EPA 40 CFR 131.36 Toxic Criteria for those States not

Complying with Clean Water Act Section 303(c)(2)(B)

EPA 40 CFR 261 Identiﬁcation and Listing of Hazardous

Waste

EPA 40 CFR 302.4 Designation of Hazardous Substances

EPA 40 CFR 355.30 (b) Emergency Release Notiﬁcation

EPA 40 CFR 370 Hazardous Chemical Reporting: Com-

munity Right To Know

EPA 40 CFR 372 Toxic Chemical Release Reporting:

Community Right-to-Know

2.8 Department of Transportation

DOT 33 CFR 153.203 Procedure for the Notice of Dis-

charge

2.9 National Fire Protection Association (NFPA)

NFPA 35 Deﬁnitions of Flammable & Combustible Sub-

stances

2.9.1 Air Quality Management Standards (AQMD)

3 STENCIL CLEANING PROCESS

3.1 Objectives for the Cleaning Process

Stencil cleanli-

ness is an essential issue for delivering the proper amount

1. www.ipc.org

2. www.ipc.org

3. www.astm.org

4. ecfr.gpoaccess.gov

5. www.answers.com/topic/united-states-department-of-defense

6. www.osha.gov/

7. www.osha.gov/

8. www.dot.gov/

9. www.nfpa.org/

IPC-7526 February 2007

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