Lead Free Manufacturing: Inspection
From B2P Portal
| Fred W. Verdi | |
| ACI Technologies, Inc. | |
| One International Plaza, Suite 600 | |
| Philadelphia, PA 19113 | |
| 3/6/09 |
Contents |
Introduction
| This Lead-Free Electronics Manufacturing Guidelines is meant to establish practices and procedures that may be used to allow the utilization of Lead-Free electronics in military systems.
These Pb-free Manufacturing Guidelines are compiled from both the hands-on experience of manufacturing, reworking, and repairing electronic systems hardware using lead-free processing at the EMPF (Electronic Manufacturing Productivity Facility), which is a COE (Center of Excellence) for U.S. Navy ManTech. This is a living document, representing benchmark presently used Pb-free electronics processing. Processes will be updated as new developments and techniques become available. |
Inspection Guidelines
Lead-free solder joints have a different appearance that tin-lead solder joints. IPC A-610D's target lead-free solder joint inspection criteria is as follows (Figure 1):
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Figure 1. Examples of IPC-A-610 Inspection Criteria. IPC-J-STD-001D and IPC A-610D were updated to reflect Lead Free Soldering, with grainy, matte appearance relative to tin-lead solder joints.
IPC A-610D, Paragraph 6.1, was included to take into account the results from using Lead-Free solders. It reaches across Class 1, Class 2, and Class 3 requirements. It allows for solder alloys which produce:
- Dull matte surface
- Gray color
- Grainy appearance
- Is considered normal for the materials or processes involved
These changes take into account the differences when using Lead-Free solders. Customer, Operators and Inspectors will have to be recalibrated to these appearance differences.
Within IPC J-STD-001D, the inspection criteria are clearly identified:
- Section 3.2.1 Solder – Lead-Free: Solder alloys less than 0.1% lead by weight not listed by J-STD-006 may be used when such use is agreed upon by the manufacturer and the user.
- Section 4.14 Solder Connection: All solder connections shall indicate evidence of wetting and adherence where solder blends to the solder surface. The solder joints should have a generally smooth appearance. A satin luster is permissible. Marks or scratches in the solder connection shall not degrade the integrity of the connection.
- There are solder alloy compositions, component lead finishes, and terminal finishes or printed board platings and special soldering processes (e.g., slow cooling with large mass PWBs) that may produce dull, matte, gray, or grainy appearing solders that are normal for the material or process involved. These solder joints are acceptable.
- Appendix E: Visual Comparisons of SnPb and Lead-Free Solder Connections
IPC-A-610D provides additional data in the inspection requirements for Lead-Free solder joints:
- Section 5.0 Soldering: The primary difference between the solder connections created with processes using tin-lead alloys and processes using Lead-Free alloys is related to the visual appearance of the solder. This standard provides visual criteria for inspection of both tin-lead and Lead-Free connections.
- Acceptable lead-free and tin-lead connections may exhibit similar appearances but Lead-Free alloys are more likely to have:
- Surface roughness (grainy or dull)
- Different wetting contact angles.
- All other solder fillet criteria are the same.
- Section 5.2.10 Soldering Anomalies – Lead-Free: Acceptable Lead-Free connections may exhibit
- Fillet Lifting – separation of the bottom of the solder and the top of the land
- Shrink holes, fissures, or hot tearing
The following are examples of tin-lead and Lead-Free solder joints (Figure 2). Typically, Lead-Free solder joints are dull and exhibit a grainy surface. Lead-Free solder joints do not exhibit positive wetting as SnPb does. As previously indicated, there are ways to improve the solderability of Lead-Free solders:
- Soldering in an inert atmosphere, such as nitrogen
- Use higher soldering temperatures
- Use more active solder fluxes.
The use of more active solder fluxes may require more aggressive cleaning processes to remove solder residues.
The Lead-Free Component Focus Group and the JCAA / JG-PP Lead-Free Soldering Program proved that it was feasible to meet IPC Class 3 requirements, with respect to solder fillet quality, wetting, and solder pad coverage.
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| Solder: Tin-lead (SnPb) Board: OSP Finish Component: SnPb Finish |
Solder: SnAgCu Board: OSP Finish Component: SnCu Finish |
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| Solder: Tin-lead (SnPb) Board: HASL Finish Component: NiPd Finish |
Solder: SnAgCu Board: HASL Finish Component: NiPd Finish |
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| Solder: Tin-lead (SnPb) Board: OSP Finish Component: Sn Finish |
Solder: SnCu Board: OSP Finish Component: Sn Finish |
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| Solder: Tin-lead (SnPb) Board: HASL Finish Component: SnPb Finish |
Solder: SnBi Board: NiAu Finish Component: SnCu Finish |
Figure 2. Examples of tin-lead and Lead-Free Solder Joints
References
1. IPC J-STD-001D - Requirements for Soldered Electrical and Electronic Assemblies, IPC Standards
2. IPC A-610D -Acceptability of Electronic Assemblies, IPC Standards
3. "Issues And Solutions To Implementing Lead-Free Soldering" by L. Whiteman. American Competitiveness Institute; SMTA Boston Conference; Boston, Massachusetts, May, 2000
4. "Test Results From The Lead-Free Component Focus Group" by L. Whiteman, American Competitiveness Institute, Philadelphia, Pa; M. Kwoka, Intersil, Palm Bay, Fl; J. Cannis, Amkor Technology Inc., Chandler, Az; G. O’Brien, Photocircuits, Glen Cove, N. Y.; D. Hillman, Rockwell Collins, Cedar Rapids, Ia; M. Toben, Shipley Ronal, Freeport, N. Y.; R. Schetty, Technic, Inc., Freeport, NY; SMTA Boston Conference; Boston, Massachusetts, May, 2002
5. "Guidelines for Lead-Free Hand Soldering" by L. Whiteman, American Competitiveness Institute, R. Northam, American Competitiveness Institute; Circuits Assembly Magazine
6. "Converting Wave Soldering Equipment From Tin-Lead To Lead-Free" by L. Whiteman, American Competitiveness Institute, J. Stong, American Competitiveness Institute, D. Alavezos, Technical Devices Company; Circuits Assembly Magazine
7. "Assembly Of JCAA/JG-PP Test Vehicles" by A. L. Campuzano-Contreras,BAE Systems, SMTA International Conference, Chicago, Illinois; September, 2005
8. "Lead-Free Process Implementation Tactics" by C. Shea, Cookson Electronics Assembly Materials Group
9. "Lead-Free Wave Soldering: Tighter Process Windows Require Tighter Controls" by C. Shea, Cookson Electronics Assembly Materials
10. "Optimizing Stencil Design For Lead-Free SMT Processing" by R. Pandher and C. Shea; Cookson Electronics Assembly Materials, SMTA International Conference, Chicago, Illinois; September, 2004
