IPC 4552 Table Of Contents
User Manual: 4552
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IPC-4552
Specification for
Electroless Nickel/
Immersion Gold (ENIG)
Plating for Printed
Circuit Boards
Developed by the Plating Processes Subcommittee (4-14) of the
Fabrication Processes Committee (4-10) of IPC
Users of this standard are encouraged to participate in the
development of future revisions.
Contact:
IPC
2215 Sanders Road
Northbrook, Illinois
60062-6135
Tel 847 509.9700
Fax 847 509.9798
ASSOCIATION CONNECTING
ELECTRONICS INDUSTRIES
®
November 6, 2002
Table of Contents
1 SCOPE ....................................................................... 1
1.1 Scope ................................................................... 1
1.2 Description .......................................................... 1
1.2.1 Phosphorus/Boron Content ................................. 1
1.3 Objective ............................................................. 1
1.4 Performance Functions ....................................... 2
1.4.1 Solderability ........................................................ 2
1.4.2 Contact Surface .................................................. 2
1.4.2.1 Membrane Switches ........................................... 2
1.4.2.2 Metallic Dome Contacts ..................................... 2
1.4.3 EMI Shielding .................................................... 2
1.4.4 Conductive (Replacement for Solder)
and/or Anisotropic Adhesive Interface .............. 2
1.4.5 Connectors .......................................................... 2
1.4.5.1 Press Fit .............................................................. 2
1.4.5.2 Edge Tab ............................................................. 2
1.4.6 Aluminum Wire Bonding ................................... 2
2 APPLICABLE DOCUMENTS ................................... 2
2.1 IPC ...................................................................... 2
2.2 ASTM International (ASTM) ............................ 2
2.3 Defense Standardization Program ...................... 2
2.4 Telcordia Technologies, Inc. .............................. 2
2.5 International Organization for
Standardization (ISO) ......................................... 2
3 REQUIREMENTS ...................................................... 3
3.1 Visual .................................................................. 3
3.2 Finish Thickness ................................................. 3
3.2.1 Electroless Nickel Thickness ............................. 3
3.2.2 Immersion Gold Thickness ................................ 3
3.3 Porosity ............................................................... 3
3.4 Adhesion ............................................................. 3
3.5 Solderability ........................................................ 3
3.6 Cleanliness .......................................................... 4
3.7 Chemical Resistance ........................................... 4
3.8 High Frequency Signal Loss .............................. 4
4 QUALITY ASSURANCE PROVISIONS ................... 4
4.1 Qualification ........................................................ 4
4.1.1 Sample Test Coupons ......................................... 5
4.2 Acceptance Tests ................................................ 5
4.3 Quality Conformance Testing ............................ 5
APPENDIX 1 Chemical Definitions ............................ 6
APPENDIX 2 Process Sequence ................................ 7
APPENDIX 3 Qualification of ENIG Process
by the Board Supplier .......................... 8
APPENDIX 4 Recommendation For Thickness
Measurement ......................................... 9
APPENDIX 5 Standard Developments Efforts
of Electroless Nickel Immersion
Gold ...................................................... 10
Figures
Figure 3-1 Uniform Plating ................................................. 3
Figure 3-2 Extraneous Plating or Nickel Foot .................... 3
Figure 3-3 Edge Pull Back ................................................. 4
Figure 3-4 Skip Plating ....................................................... 4
Figure 4-1 IPC-2221 Test Speciman M, Surface Mount
Solderability Testing, mm [in] ............................ 5
Figure 1 Results from Gold Thickness Survey ............. 11
Figure 2 Results from Nickel Thickness Survey ........... 12
Figure 3 Comparison of Gold Thickness Values
by XRF Machine Type .................................... 14
Figure 4 Comparison of Gold Plating Thickness
Variation by Vendor for Similar Bath Life
Conditions ....................................................... 15
Figure 5 Comparison of Nickel Plating Thickness
Variation by Vendor for Similar Bath Life
Conditions ....................................................... 16
Figure 6 Wetting Times as a Function of Plating
Dwell Times for Vendor D, 90 Days Old ........ 17
Figure 7 Wetting Times as a Function of Plating
Dwell Times for Vendor D, 90 Days Old ........ 18
Figure 9 Wetting Balance Data for Vendor D Post
18 Hours 85/85 Conditioning .......................... 20
Figure 10 Comparison of One Microinch Gold
Deposit Tested at 8 Months Shelf Life
vs as Received and 85/85 .............................. 21
Figure 11 Comparison of One Microinch Gold
Deposit after Various Storage Times/
Conditions ....................................................... 21
Figure 12 Contact Resistance Data for Vendor D
for Interlocking Square Contacts .................... 22
Figure 13 Contact Resistance Data for Vendor C
for Interlocking Square Contacts .................... 23
Figure 14 Comparison of Gold Thickness by Vendor
for the Interlocking Square Contact Test ........ 24
Figure 15 Interlocking Square Contact Test Coupon ...... 25
Tables
Table 3-1 Requirements of Electroless Nickel Immersion
Gold Plating ......................................................... 1
Table 4-1 Qualification Test Coupons ................................. 5
IPC-4552 October 2002
iv
Specification for Electroless Nickel/Immersion
Gold (ENIG) Plating for Printed Circuit Boards
1 SCOPE
1.1 Scope This specification sets the requirements for
the use of Electroless Nickel/Immersion Gold (ENIG) as a
surface finish for printed circuit boards. This specification
is intended to set requirements for ENIG deposit thick-
nesses based on performance criteria. It is intended for use
by supplier, printed circuit manufacturer, electronics manu-
facturing services (EMS) and original equipment manufac-
turer (OEM).
1.2 Description ENIG is an electroless nickel layer
capped with a thin layer of immersion gold. It is a multi-
functional surface finish, applicable to soldering, aluminum
wire bonding, press fit connections, and as a contact sur-
face. The immersion gold protects the underlying nickel
from oxidation/passivation over its intended life. However,
this layer is not totally impervious and it will not pass the
requirements of a ‘classic’ porosity test.
1.2.1 Phosphorus/Boron Content Phosphorus or boron
containing reducing agents are used for the reduction of the
electroless nickel during the deposition process. Phospho-
rus or boron is thus incorporated in the nickel deposit. The
level of these co-deposited elements should be controlled
within the specified process limit. Variation of phosphorus
or boron level, outside the specified process limits, may
have adverse effects on the solderability of the finish.
1.3 Objective This specification sets the requirements
specific to ENIG as a surface finish (see Table 3-1 for a
summary of these requirements). As other finishes require
specifications, they will be addressed by the IPC Plating
Processes Subcommittee as part of the IPC-4550 specifica-
tion family. As this and other applicable specifications are
under continuous review, the subcommittee will add appro-
priate amendments and make necessary revisions to these
documents.
Table 3-1 Requirements of Electroless Nickel Immersion Gold Plating
Tests Test Method Requirement
Paragraph Class 1 Class 2 Class 3
General
Visual Visual 3.1 Uniform plating and complete
coverage of surface to be plated.
Electroless Nickel Thickness APPENDIX 4 3.2.1 3to6µm
[118.1 to 236.2 µin]
Immersion Gold Thickness APPENDIX 4 0 0.05 µm minimum
[1.97 µin minimum]
Porosity N/A 3.3 N/A
Physical
Adhesion/Tape Test IPC-TM-650
TM 2.4.1 3.4 No evidence of plating removed.
Solderability J-STD-003 3.5 Meet solderabiltiy requirements of Category 3
durability with six months shelf life.
Chemical
Phosphorous/Boron Content ASTM B-733-97
& ASTM
B607-91 (1998) 1.2.1 (Reference Only; Supplier Dependent -
No Testing Required)
Chemical Resistance N/A 3.7 N/A
Electrical
High Frequency Signal Loss
(1)
3.8 TBD
Contact Resistance
(1)
1.4.2 TBD
Environmental
Cleanliness IPC-TM-650
TM 2.3.25 3.6 Max. 1.56 µg/cm
2
(1) An appropriate IPC-TM-650 test method used to generate data for this electrical property is not available at the time of this writing.
October 2002 IPC-4552
1
