IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG - 第42页

APPENDIX 5 ENEPIG PWB Surface Finish Wetting Balance Testing Gerar d O’Brien, President S T and S Group. INTRODUCTION Consistent with all previous speciﬁcation generations by the 4-14 Subcommittee for PWB surface ﬁnishes…

Above Figure A4-SS-4 shows typical ENEPIG plated on one ounce Cu/epoxy sample when measured with a pin diode detec-

tor. Note how Au L-β and Br K-α peaks are better resolved and the Au L-α peak is visible and distinct from Cu K-β, allow-

ing measurement of Au intensity without need for peak overlap corrections like peak deconvolution. Also note clear Pd peak

with low background noise.

Figure A4-SS4 XRF Spectrum of ENEPIG Plated on 1 oz Cu/Epoxy

ENEPIG pin diode.cts

2.7

16005

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6402

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Count

KeV

16.8 21.6 26.3

January 2013 IPC-4556

Spectral Analysis Mode·WPHA

Ele Edt Yiew Display Ogerations BOl Help

FLE 1:ENIPIG_pin diode.cts

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Mn [Ka]

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Peak (Ch.,KeV,Cts)

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APPENDIX 5

ENEPIG PWB Surface Finish

Wetting Balance Testing

Gerard O’Brien, President

S T and S Group.

INTRODUCTION

Consistent with all previous speciﬁcation generations by the 4-14 Subcommittee for PWB surface ﬁnishes, solderability test-

ing using a wetting balance was performed to evaluate ENEPIG both in the ‘‘as received’’ condition and post temperature/

humidity stressing. There were six chemical suppliers who submitted samples for testing and because of their geographical

locations and the time needed to complete the plated test vehicles, some sample groups had signiﬁcant ‘‘shelf life’’ prior to

testing of up to eight months. During this time, the samples remained in their original packaging.

Test Vehicle The 4-14 Subcommittee which works closely

with the 5-23A Task Group has settled on a wetting balance

coupon that has changed little over the last 5 years or so. The

latest iteration of the test coupon was built with 18 wetting

balance coupons and four ball shear coupons per array (see

Figure A5-1). The wetting balance coupon also contains the

NPL spread test vehicle, which was also used during the gen-

eration of this speciﬁcation and retains through holes at the

opposite side (which were not used in these tests). The acid

copper plating and soldermask operations required to fabricate

these coupons were generously provided to the group by Mr.

Luc Beauvillier, who was then with Via Systems - Oregon.

Following extensive intra-committee discussions on the target thicknesses for the speciﬁcation, it was proposed that initial

testing would be on samples plated to the following thickness requirements:

1) Electroless Nickel - 6 microns ± 1 micron

2) Electroless Palladium - 0.1, 0.2 and 0.3 microns nominally - no tolerance was set

3) Immersion Gold - the thickness would be ‘‘as supplied’’

4) Electroless Palladium at 0.5 microns nominal from two of the six suppliers, in order to evaluate a ‘‘heavy’’ palladium

Figure A5-1 Example of the Wetting Balance Coupon

deposit (see Table A5-1)

Six chemical suppliers took part by providing plated test vehicles:

1) Atotech

2) Dow Electronic Materials

3) Enthone

4) MacDermid

5) OMG

6) Uyemura (both U.S. and Japanese plated)

Used for the Testing of ENEPIG

Table A5-1 XRF Measurements of the Nominal 0.5 micron Electroless Palladium Samples

Supplier Identiﬁer

Immersion Gold

Thickness (microns)

Electroless Palladium

Thickness (microns)

Electroless Nickel

Thickness (microns)

Target Thickness Per individual supplier 0.5 5 - 6

F 0.038 0.51 4.98

G 0.016 0.45 6.67

IPC-4556 January 2013

Some of these suppliers submitted ENEPIG samples that used

a phosphorus-containing reducing agent in the electroless pal-

ladium bath, whose deposits contain approximately 2 to 4

wt% phosphorus, while others submitted samples using other

non-phosphorus containing reducing agents, whose deposits

are sometimes classiﬁed as ‘‘pure palladium.’’ The samples

remained in their original packaging until the ﬁnal ones had

been received for testing. This took some time in the case of

some suppliers and, when ready to commence the test, some

ENEPIG samples had 8 months of ‘‘natural’’ shelf life. Once

all samples were received, the packages were opened and each

group assigned a Roman numeral corresponding to a speciﬁc

nominal electroless palladium thickness and supplier - this

was marked on the edge rail of the array with an electric pen-

cil to avoid surface contamination of the plating. XRF read-

ings, using a PIN diode system with a measurement time of

sixty seconds, were generated for all sample groups. As can be

seen from the graphs (Figures A5-2 through A5-4), some of

the suppliers did not correctly measure the deposit at their

location, something that has been a major issue with the intro-

duction of ENEPIG. Additionally, one supplier chose to sub-

mit samples with two different immersion gold thicknesses.

The thinner of these two samples turned out to be of great

value to the committee, as it produced solderability failures

when stressed.

Solderability testing was performed on a Metronelec ST88

wetting balance (see Figure A5-5), using a solder bath for

coupon testing. Testing followed the requirements of the IPC

J-STD-003 B Solderability Standard and samples were tested

with both SAC305 and Eutectic SnPb solders. As per the stan-

dard, test temperatures of 255 °C and 235 °C were used for

the SAC305 alloy and the Eutectic SnPb alloy, respectively.

For the testing, a new charge of solder was used for each

alloy. Similarly per the Standard, Test Fluxes # 1 and # 2 were

used for Eutectic SnPb and SAC305 alloys, respectively.

The test coupons were removed from the array, the edges

carefully ‘‘wiped’’ over 1200 grit silicon carbide paper and

then wiped with a paper towel to remove any dust, to ensure

that no epoxy smear was present on the edge of the SMT pads

on the coupon that might prevent contact with the solder and

produce a false result.

Following coupon preparation, each coupon was immersed

into the appropriate ﬂux for the alloy being used for ﬁve sec-

onds, excess ﬂux being allowed to drain. The coupon was then

placed into a suitable tool holder and immersed to a depth of

0.5 mm at 90 degrees incident to the solder surface. A dwell

time of ten seconds was used for each coupon. Following the

test, the sample was inspected to conﬁrm the wetting balance

results and the next coupon from that group run. Ten samples

per group were run for the ‘‘as-received’’ condition. Results

are shown in Figures A5-6 - A5-15.

IPC-4556-a5-2

Figure A5-2 XRF Measurements of Gold and Palladium Thick-

nesses Supplied as Nominal 0.1 micron Electroless Palladium

0.1 microns Palladium

0.160

0.140

0.120

0.100

0.080

0.060

0.040

0.020

Gold

Palladium

0.000

microns

BCDEFG

IPC-a5-3

Figure A5-3 XRF Measurements of Gold and Palladium Thick-

nesses Supplied as Nominal 0.2 micron Electroless Palladium

0.2 microns Palladium

0.350

0.300

0.250

0.200

0.150

0.000

0.050

Gold

Palladium

0.000

microns

ABCDEFG

IPC-4556-a5-4

Figure A5-4 XRF Measurements of Gold and Palladium Thick-

nesses Supplied as Nominal 0.3 micron Electroless Palladium

0.2 microns Palladium

0.350

0.300

0.250

0.200

0.150

0.000

0.050

Gold

Palladium

0.000

microns

ABCDEFG

Figure A5-5 Metronelec ST88 Wetting Balance Used for the

Testing

January 2013 IPC-4556

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