IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG - 第18页

Note: Some designs may not have feature sizes of this speciﬁed pad area and will require the use of alternate pad sizes. The XRF collimator used shall always be smaller than the pad used for measurement; and speciﬁcally …

3.2 Finish Thickness Thicknesses of the electroless nickel,

electroless palladium and immersion gold layers shall be mea-

sured and veriﬁed following the completion of the ENEPIG

plating operation in the printed board fabrication process. The

use of X-ray ﬂuorescence (XRF) methodology for thickness

determination shall be in accordance with APPENDICES 4

and 9 of this document and shall employ XRF instrumentation

equipped with software and hardware appropriate for ENEPIG

measurement. The committee has performed extensive round

robin testing of equipment capability to accurately measure

this tertiary deposit (see APPENDICES 3, 9 and 10). The

results showed a number of critical issues with equipment,

set-up, measuring protocols and reference standards. It is

imperative to demonstrate measurement capability in order to

meet the following thickness speciﬁcation.

3.2.1 Electroless Nickel Thickness The electroless nickel

thickness shall be 3 to 6 µm [118.1 to 236.2 µin] at ± 4 sigma

(standard deviations) from the mean as measured on a nominal pad size of 1.5 mm x 1.5 mm [0.060 in x 0.060 in] or equiva-

lent area, where standard feature size tolerances as expressed in the IPC-6010 standard series, apply. This upper end of this

thickness speciﬁcation has been chosen based on concerns with insertion force issues for compliant pin applications ONLY.

Use of thicknesses outside of this range shall be AABUS.

3.2.2 Electroless Palladium Thickness The electroless palladium thickness shall be 0.05 to 0.30 µm [2 to 12 µin] at ± 4

sigma (standard deviations) from the mean as measured on a nominal pad size of 1.5 mm x 1.5 mm [0.060 in x 0.060 in] or

equivalent area, where standard feature size tolerances as expressed in the IPC-6010 standard series, apply. The upper thick-

ness limit may be exceeded to meet speciﬁc design criteria (for example, applications requiring wire bonding but no solder-

ing).

3.2.3 Immersion Gold Thickness The minimum immersion gold thickness shall be >0.030 µm [1.2 µin] at - 4 sigma

(standard deviations) below the mean as measured on a nominal pad size of 1.5 mm x 1.5 mm [0.060 in x 0.060 in] or

equivalent area, where standard feature size tolerances as expressed in the IPC-6010 standard series, apply. The speciﬁcation

is one sided, based on performance test results showing impaired solderability performance after accelerated aging at lower

gold thicknesses. The nature of the reaction of immersion gold with electroless palladium is such that substantially greater

thicknesses may not be achievable.

Figure 3-11 TEM Image of a Normal ENEPIG Deposit

[The Palladium-Phosphorus ﬁlm is amorphous and very uniform whereas the gold (Au) deposit is crystalline in nature.]

Figure 3-12 2500X Image of Nickel that is Hyper-Corroded

(This is due to excessive dwell time in the gold bath.)

January 2013 IPC-4556

×2.5K

20kV

20 m

60 nm

TEM image

Au deposit

Palladium

deposit

EN deposit

推着额期

Electron diffraction of

Palladium film

Note: Some designs may not have feature sizes of this speciﬁed pad area and will require the use of alternate pad sizes. The

XRF collimator used shall always be smaller than the pad used for measurement; and speciﬁcally, the collimator shall not

exceed 30% of the feature pad size being measured. For smaller sized pads, the measurement time will need to increase

proportionately as a function of collimator area reduction. Consistency of the pad size used for measurement is of primary

concern in order to obtain a statistically valid result, due to the typical plating thickness variation seen as a function of pad

size. In general, smaller features will plate thicker than larger features. The use of ﬁducial pads for this measurement is sug-

gested for those designs not having the speciﬁed pad feature areas, described above.

3.2.4 XRF Calibration Standards The use of National Standards traceable calibration standards with similar thicknesses to

the speciﬁed ENEPIG thicknesses which are to be measured, is recommended. Tri-layer standards where Au and Pd are

plated directly on Ni/Cu/PCB should be used for calibration for Cu thicknesses >30 µm. Tri-layer foil standards where Au

and Pd are plated on a Ni-foil should be used if boards with varying Cu-thicknesses are to be measured. Additional infor-

mation can be found in Appendix 10.

For Cu thickness >30 µm, a combination of a minimum of two calibration standards with approximate thicknesses, as below,

should be used.

• Au/Pd/Ni/Base 0.05 µm/0.02 µm/3 µm/>30 µm

• Au/Pd/Ni/Base 0.05 µm/0.09 µm/3 µm/>30 µm

• Au/Pd/Ni/Base 0.05 µm/0.3 µm/3 µm/>30 µm

• Au/Pd/Ni/Base 0.1 µm/0.2 µm/3 µm/>30 µm

For Cu thicknesses <30 µm a combination of a minimum of two calibration foil standards with approximate thicknesses as

below, should be used.

• Au/Pd/Ni/Base 0.06 µm/0.02 µm/4 µm/<30 µm

• Au/Pd/Ni/Base 0.06 µm/0.06 µm/4 µm/<30 µm

• Au/Pd/Ni/Base 0.05 µm/0.1 µm/4 µm/<30 µm

• Au/Pd/Ni/Base 0.05 µm/0.25 µm/4 µm/<30 µm

For additional details, see APPENDICES 4 and 9.

3.2.5 Use of Non-Statistical Thickness Specification For production lot sizes of ten printed boards or less, i.e., proto-

type builds, the need to demonstrate compliance to the statistical requirements above are negated, provided that measure-

ments are taken on 100% of all printed boards/panel coupons, thus providing population parameters rather than sample sta-

tistics. All such readings shall fall within the thickness ranges speciﬁed above for all three deposits. Any readings below or

above the speciﬁed thickness range shall be cause for rejection of that board.

3.2.6 Production Overruns and/or Inventory Items When compliance testing of individual printed board(s) remaining in

inventory is required, use the protocol of 3.2.5. For production overruns larger than ten, the sample statistic constraints shall

apply.

3.3 Porosity An ENEPIG immersion gold layer is not totally impervious and is not able to pass the requirements of a

‘classic’ porosity test (for example, Nitric Acid per ASTM B 735).

3.4 Adhesion The purpose of adhesion testing for ENEPIG ﬁnished boards is twofold.

1) The primary purpose of the testing is to verify that there is no adhesion failure between the metallic layers of the ﬁn-

ish, or the ﬁnish and the base metal. The tape testing shall be carried out in accordance with IPC-TM-650, Method

2.4.1, using a strip of pressure sensitive tape. There shall be no evidence of any portion of the surface ﬁnish being

removed, as shown by particles of plated deposit/pattern adhering to the tape. If soldermask overhang breaks off and

adheres to the tape, it is evidence of undercut but not of adhesion failure.

2) The secondary purpose is for testing the adhesion of the solder mask to both traces and laminate. Both the chemistry

used in the ENEPIG process and the required dwell times and temperatures can have a negative impact on solder mask

adhesion. – Note: Not all solder masks are compatible with an ENEPIG process.

In both cases, testing should be conducted on regions of high feature density on the board, such as BGA sites, dams between

ﬁne pitch leaded devices or over areas of high trace density. Using the same approach as for the test for metal adhesion,

check for evidence of the soldermask being removed, as shown by particles of soldermask adhering to the tape.

IPC-4556 January 2013

Because of the requirement to test in high density areas, the potential to leave tape residue that could interfere with solder-

ing exists, especially if an incorrect type of tape is used. Veriﬁcation of zero impact to solderability must be demonstrated

for the areas tested, or the area tested shall not be used for ﬁnal product.

3.5 Solderability The thickness speciﬁcation described herein shall meet the Category 3 coating durability requirements of

J-STD-003, i.e., greater than 12 months shelf life.

Note 1: The use of steam exposure (conditioning) is not an applicable accelerated stress test method for ENEPIG.

Note 2: While adherence to the IPC-1601 recommendations for baking prior to assembly may have a negative impact on

solderability performance, the requirements for solderability testing in this speciﬁcation are for samples tested without bak-

ing. Any deviation from this shall be AABUS.

For details of the solder spread testing data from the round robin, see APPENDIX 6. Ball shear data from the same study is

documented in APPENDIX 7.

3.5.1 Force Measurement Testing (Wetting Balance Test-

ing)

The following requirements are based on the use of the

Standard IPC coupon, Figure 3-13, immersed to a depth of

0.6mm at 90 degrees incidence to the solder surface. The

dwell time shall be ten seconds. For details of the wetting bal-

ance data from the round robin study, see APPENDIX 5.

• Force measurement testing of an ‘‘as received’’ sample with

Eutectic SnPb solder, using the prescribed Test Flux#1at

235 °C, shall produce a positive wetting force within 2 sec-

onds and a minimum wetting force of 0.14 mN/mm.

• For force measurement testing of samples stressed for 8

hours @ 72 °C [162 °F] and 85% R.H, the increase in wet-

ting time shall not exceed 1 second. The wetting force shall

be a minimum of 0.12 mN/mm.

• For force measurement testing of ‘‘as received’’ samples with SAC305 solder, using the prescribed Test Flux#2at

255 °C, shall produce a positive wetting force within 1.5 seconds and a minimum wetting force of 0.19 mN/mm.

• For force measurement testing of samples stressed for 8 hours @ 72 °C [162 °F] and 85% R.H., the increase in wetting

time shall not exceed 1 second. The wetting force shall be a minimum of 0.17 mN/mm.

3.6 Cleanliness The surface of an ENEPIG ﬁnish is typically cleaner than most other surface ﬁnishes. Ionic cleanliness

shall be established per the requirements of IPC-5704, which speciﬁes a sample size of 11. It is recommended that solvent

extract conductivity (SEC) testing per IPC-TM-650, Method 2.3.25, also be performed at the same time as the IPC-5704

qualiﬁcation, to establish process control parameters. SIR testing shall be per IPC-TM-650, Method 2.6.3.5. The require-

ments for SIR test performance shall be as speciﬁed in Table 3-1. Failure to meet this cleanliness speciﬁcation should trigger

immediate process control corrective action.

3.7 Electrolytic Corrosion The ENEPIG process contains chemistries that are ionic in nature, but which are readily rinse-

able. Both the quality and volume of water used for the rinsing steps between process baths, and for the ﬁnal rinsing of the

product are critical if the potential for electrolytic corrosion is to be avoided. The use of IPC-TM-650, Method 2.6.14.1,

‘‘Electrochemical Migration Resistance Test’’ is recommended for high reliability applications, or for designs with high fea-

ture density. The resistance values shall not drop more than one order of magnitude after the test has been completed.

4 QUALITY ASSURANCE PROVISIONS

4.1 General Quality Assurance Provisions

These are speciﬁed in IPC-6011 and each IPC-60XX sectional speciﬁcation.

Additional requirements for printed boards with electroless nickel/electroless palladium/immersion gold (ENEPIG) plating

are speciﬁed herein for qualiﬁcation, acceptance, and quality conformance.

Figure 3-13 The Standard IPC Force Measurement

4.1.1 Qualification Recommendations Qualiﬁcation of a printed board supplier, supplying ENEPIG to this speciﬁcation

shall be AABUS (see IPC-6011). The process capability of a supplier of PWB with ENEPIG ﬁnish shall be established by

demonstrating process control over time. Table 4-1 provides a listing of suggested qualiﬁcation elements that should be exer-

cised by the supplier. It includes the associated requirements and/or test methods when applicable.

Coupon

January 2013 IPC-4556