IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG - 第83页

SUMMARY The electroless Ni, electroless Pd, and immersion Au (ENEPIG) surface ﬁnish is capturing the attention of both the struc- tural and electronics soldering communities as a means to enhance the solderability of com…

Test Results - Wetting Rate (W

) The wetting rate behavior was also assessed for these ﬁnishes. Generally speaking, there

were only small decreases in the wetting rate as a function of increased aging time in the Class 2 environment. The same

trend was observed across all three candidate ENEPIG ﬁnishes (Figure A11-3). Auger Electron Spectroscopy (AES) was

used to determine the source of the slower wetting behavior. The primary cause was attributed to a small amount of Pd that

had diffused through the Au to the surface. The driving force for that diffusion is a combination of the elevated temperatures

and oxidization potential established by the air environment above the sample. The Pd proceeded to oxidize, thus, slowing

the wetting and spreading process. A secondary factor may be a slight buildup of carbon compounds detected by AES on the

Au surface. The small decreases in wetting rate would not impact an actual manufacturing process.

IPC-4556-a11-3

Figure A11-3 Wetting Rate as a Function of Battelle Class 2 Aging – Both vendors1&2using Sn63Pb37 solder, RMA ﬂux and 245

°C max. temperatures.

Wetting Rate (mN/sec)

100

As Fabricated 8.4hrs 33.6hrs 168hrs 336hrs

ENEPIG Sn63-Pb37

245C

Wetting Rate V1 Thick Pd

Wetting Rate V2 Thin Pd

Wetting Rate V2 Thick Pd

Aging Time (hrs)

IPC-4556 January 2013

SUMMARY

The electroless Ni, electroless Pd, and immersion Au (ENEPIG) surface ﬁnish is capturing the attention of both the struc-

tural and electronics soldering communities as a means to enhance the solderability of common base materials for a range

of applications. Solderability testing has illustrated the robustness of this ﬁnish after simulated storage aging using the

Battelle Class 2 environment. For the various ENEPIG ﬁnishes in this study, the excellent performance was sensitive to sup-

plier but not to the thickness of the Pd layer. Only a slight decrease in wetting rate was observed after exposure to the

Battelle Class 2 conditions. Auger electron spectroscopy (AES) identiﬁed two possible sources of the reduced wetting rate:

(a) Pd diffusion to the Au surface and its oxidation and (b) the small build-up of carbon compounds that are attracted to the

Au layer.

REFERENCES

1. G. Milad, Is ‘‘Black Pad’’ Still an Issue for ENIG?’’ Circuit World, Vol. 36 Iss: 1, pp.10 - 13, 2010.

2. W. H. Abbott, ‘‘The Development and Performance Characteristics of Mixed Flowing Gas Test Environment,’’ IEEE

Transactions, Vol. 11, No. 1, March 1988.

3. A. Jackson, I. Artaki, and P.Vianco, ‘‘Manufacturing Feasibility of Several Lead Free Solders for Electronic Assembly,’’

Proc. 7

h Inter. SAMPE Electronics Conf. (Parsippany, NJ; June 21, 1994), p. 381.

4. I. Artaki, A. Jackson, and P. Vianco, ‘‘Fine Pitch Surface Mount Assembly with Lead-Free, Low Residue Solder Paste,’’

Proc. Surface Mount Inter., (San Jose, CA Aug. 28, 1994), p. 495.

5. P. Vianco, J. Rejent, I. Artaki, and U. Ray, ‘‘An Evaluation of Prototype Circuit Boards Assembled with a Sn-Ag-Bi Sol-

der,’’ Proc. IPC Works ’99 (IPC, Northbrook, IL; 1999), p. S-03-3-1.

6. P. Vianco and A. Claghorn, ‘‘Effect of Substrate Preheating on Solderability Performance as a Guideline for Assembly

Development - Part I: Baseline Analysis,’’ Soldering and Surface Mount Technology No. 24 (1996) p. 12.

7. R. J. K. Wassink, Soldering Electronics, (Ayr, Scotland: Electrochemical Publications Limited, 1984) p. 235.

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