IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG - 第19页

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. V eriﬁcation of zero impact to …

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

4.1.2 Sample Test Coupons Test specimens used for qualiﬁcation of printed boards with ENEPIG ﬁnish may be found in

IPC-2221 and/or noted in IPC-6010 sectional speciﬁcations. Alternatively, the supplier may create test patterns or process

control coupons to accommodate qualiﬁcation testing and/or lot conformance deposit thickness measurements. Specimen(s)

should be obtained or developed for qualiﬁcation testing to the requirements listed in Table 4-1.

Table 4-1 Suggested Fabricator Qualiﬁcation Plan

Requirement Test Reference Remarks

XRF Certiﬁcation Suitably calibrated XRF instrument with detector

capable of measuring tri-level thin coatings.

Use of certiﬁed national ENEPIG standards as

referenced in Appendices 3, 4, 9 and 10.

Note: Do not use electrodeposited standards or ones

with thicknesses outside the target thickness range

under evaluation.

Perform XRF certiﬁcation by performing a gauge

R&R or equivalent statistical approach. Use of the

correct certiﬁed national standards is critical. This

data may be used as to begin building a suitable

deposit thickness distribution database.

Deposit Thickness

Distribution

Suitable test pattern or production board/panel

having the correct surface area pads as described in

Appendices 3, 4, 9 and 10.

The deposit thickness database to demonstrate 4

sigma distribution should include sample readings

from product processed through the production

baths. Include readings from both front and. back

of the panels. Also, map thickness as a function of

panel position within a basket. It is suggested that

thickness measurements be made at panel locations

that provide as complete panel coverage as possible,

e.g., diagonal, four corners and center, each PWB

within a panel.

Visual Ref. paragraph 3.1 Perform visual inspection per applicable requirements

at a production ﬁnal inspection workstation and

document the appearance of the ﬁnish. It is

recommended to create an inspection checklist.

Solderability

(Wetting Balance)

Use suitable coupon(s) to perform J-STD-003

Category 3 testing.

See paragraphs 3.5 and 3.5.1.

Note: IPC-1601 provides guidance on packaging and

handling of coupons.

It is recommended to qualify to Category 3,

the highest level of storage coating durability

in J-STD-003.

Wire Bondability Test specimen suitable for use with MIL-STD 883,

METHOD 2011.8, or user deﬁned test pattern/

speciﬁcation.

Method 2011.8 of MIL-STD-883 is the most

commonly used test method requirement for

determining wire bond strength. Other user-deﬁned

AABUS measurements may be required. Document a

sufficient quantity of bond pulls to establish capability.

Assistance by the user may be required to support

this method.

Ionic Cleanliness Suitable specimen for IPC-5704

Ion Chromatography (IC) Testing.

IC testing per IPC-5704 is recommended during

qualiﬁcation to conﬁrm that the process and

associated rinses are adequate to ensure that no

contaminates remain that might not meet next level

assembly requirements. Periodic re-qualiﬁcation may

be necessary to account for changes in materials

and processes.

PTH Coverage Suitable Through Hole specimens for

microsectioning.

Microsection a number of ‘‘as received’’ specimen(s)

using darkﬁeld illumination (before solder ﬂoat).

Utilize coupon specimens from a variety of locations,

for example, from the outside and center panels of a

basket load.

Effect on

Soldermask

Adhesion

Para 3.4 - Suitable coupon of IPC-2221 or production

part containing high density features.

Utilizing an appropriate specimen, benchmark

adhesion of solder mask. Inspect to Quality

conformance requirements, or as speciﬁed

by User. Note whether the solder mask was

applied before or after ENEPIG processing.

Repeatability at

Various Stages of

Loading and Bath

Life

Applicable specimens of the Qual Plan. Repeat aspects of the Qualiﬁcation Testing at various

bath life metal turn-over (MTO) stages, as applicable,

looking for any impacts on deposition thickness or

distribution, (for example, for new baths and late

MTO).

IPC-4556 January 2013