Inspection Guidelines
Lead Free solder joint have a different appearance that Tin Lead solder joints. IPC A-610C’s target inspection criteria is as follows (Figure 13):
- SnPb bright shiny appearance
- Smooth surface
- Good wetting, with respect to pad and lead coverage
IPC-A-610 Inspection Criteria
- SnPb bright shiny appearance
- Smooth surface
- Good wetting, with respect to pad and lead coverage
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Figure 13. Examples of IPC-A-610 Inspection Criteria
IPC A-610C, 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 criterion is 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. Figures specific to Lead Free connections will be identified with the symbol.
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 14). 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 |
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Figure 14. Examples of Tin Lead and Lead Free Solder Joints
