IPC-4556 印制板化学镍钯浸金（ENEPIG）规范ENG.pdf - 第11页

Specification for Electroless Nickel/Electroless Palladium/ Immersion Gold (ENEPIG) Plating for Printed Circuit Boards 1 SCOPE 1.1 Statement of Scope This speciﬁcation sets the requirements for the use of Electroless Nic…

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IPC-4556 January 2013

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Specification for Electroless Nickel/Electroless Palladium/

Immersion Gold (ENEPIG) Plating for Printed Circuit Boards

1 SCOPE

1.1 Statement of Scope

This speciﬁcation sets the requirements for the use of Electroless Nickel/Electroless Palladium/

Immersion Gold (ENEPIG) as a surface ﬁnish for printed boards. This speciﬁcation sets requirements for ENEPIG deposit

thicknesses for applications including soldering, wire bonding and as a contact ﬁnish. It is intended for use by chemical

suppliers, printed board manufacturers, electronics manufacturing services (EMS) and original equipment manufacturers

(OEM).

1.2 Description ENEPIG is a tertiary layered surface ﬁnish plated over copper as the basis metal. ENEPIG consists of an

electroless nickel base layer over which is plated an electroless palladium barrier layer followed by a deposit of a thin

immersion gold as the ﬁnal outer layer. For deposition process details, see APPENDIX 1 of this speciﬁcation. It is a multi-

functional surface ﬁnish, applicable to soldering and to gold, aluminum and copper wire bonding. It is also suitable as the

mating surface for soft membrane and steel dome contacts. Additional applications include use in Low Insertion Force (LIF)

and Zero Insertion Force (ZIF) edge connectors and for press-ﬁt applications. The electroless palladium layer forms a dif-

fusion barrier that impedes nickel diffusion to the gold surface. The immersion gold protects the palladium layer from react-

ing with contaminants prior to processing that might otherwise affect joining processes, such as wire bonding and soldering.

1.2.1 Electroless Nickel Reducing Agents - Phosphorus Content Phosphorus-containing, reducing agents are typically

used for the reduction of the electroless nickel during the deposition process and phosphorus is incorporated in the nickel

deposit. The level of this co-deposited element should be controlled within the suppliers speciﬁed process limits. Variation of

phosphorus levels outside the speciﬁed process limits may have adverse effects on the performance of the ﬁnish.

1.2.2 Electroless Palladium Reducing Agents There are two distinct classes of reducing agents used in electroless pal-

ladium baths currently available for use in the ENEPIG process, those that produce deposits that contain a co-deposited ele-

ment such as phosphorus, and those that produce an essentially pure palladium deposit. The level of the co-deposited ele-

ments should be controlled within the speciﬁed process limits. Examples of electroless palladium deposit from both these

classes have been evaluated during the development of this speciﬁcation and no perceivable differences in performance were

observed in the tests of solderability or wire bondability

1.3 Objective This speciﬁcation sets the requirements for ENEPIG as a surface ﬁnish (see Table 3-1 for a summary of

these requirements). As additional surface ﬁnishes require speciﬁcations, they will be addressed by the IPC Plating Processes

Subcommittee as part of the IPC-455X speciﬁcation family. This and other surface ﬁnish speciﬁcations are under continuous

review. The 4-14 subcommittee will make appropriate amendments or revisions to these documents as required. The 4-14

Plating Processes Subcommittee undertook a ‘‘Round Robin’’ study to generate data to support the recommendations sited

for the various aspects of this speciﬁcation. For an outline of the study, refer to APPENDIX 2.

1.3.1 Order of Precedence In the event of conﬂict, the following order of precedence shall apply:

1. The purchase order. This includes AABUS exceptions to this speciﬁcation.

2. The master drawing. This includes AABUS exceptions to this speciﬁcation.

3. This speciﬁcation.

4. Applicable documents as detailed in Section 2 of this document.

1.3.1.1 Appendices This speciﬁcation contains eleven Appendices provided for information which are included after the

main body of this document. Be aware that none of the content of these appendices are binding requirements unless sepa-

rately and speciﬁcally speciﬁed herein, or as required by purchase order, master drawing, other applicable documents, or as

established AABUS.

1.4 Performance Functions

1.4.1 Solderability

One of the two primary functions of ENEPIG is to provide a solderable surface ﬁnish capable of pro-

viding IPC Category 3 shelf life (minimum 12 months) per IPC-J-STD-003 testing. This shelf life is suitable for all surface

mount, hybrid and through-hole assembly applications. The use of electroless palladium as a diffusion barrier between the

January 2013 IPC-4556

nickel and the gold mitigates the potential for hyper-corrosion of the electroless nickel deposit, thus enhancing its solder-

ability and solder joint reliability. The minimal thicknesses of the electroless palladium and of the immersion gold deposit

make the possibility of embrittlement of the solder joint by palladium or gold negligible. It is the responsibility of the user

to calculate the percentage of both gold and palladium in the resulting solder joint where mounting pad sizes associated with

0201 or smaller components are encountered and compare these calculated levels of gold or palladium to the 3% threshold

values believed to give rise to solder joint embrittlement.

1.4.2 Wire Bonding The second primary function of ENEPIG is to provide a wire bondable surface ﬁnish suitable for

gold, aluminum and copper wire applications. ENEPIG has been found to meet the requirements of MIL-STD-883, Method

2011.8. The committee has performed extensive testing with gold wire (see APPENDIX 8) and has received additional anec-

dotal data from members conﬁrming the suitability of this ﬁnish for aluminum and copper wirebonding. Variables that are

likely to affect performance include cleanliness, substrate materials, wire thickness and substrate copper surface roughness,

as ENEPIG deposits are not capable of completely levelling the substrate surface. During the development of this speciﬁ-

cation, surface roughness values of up to an Ra value of 389 nm have been tested with no negative impacts on gold wire

bond strength.

1.4.3 Contact Surface There is a substantial amount of experience using ENEPIG for the applications listed below in

1.4.3.1 and 1.4.3.2.

1.4.3.1 Membrane Switches ENEPIG is a de facto standard for soft touch membrane switches.

ENEPIG plated samples tested for 2 million contact actuations showed negligible change in contact resistance. For these

actuations, the average deposit thicknesses were nominally: 4.65 µm [183 µin] of electroless nickel (EN), 0.13 µm [5.2 µin]

of electroless palladium (EP) and 0.053 µm [2.1 µin] of immersion gold (IG).

Note: This test was run to the full number of cycles with no visible impact on the ENEPIG deposit.

1.4.3.2 Metallic Dome Contacts ENEPIG has been demonstrated to be suitable for use with metallic (stainless steel), cir-

cular dome contacts, based on testing to 1 million cycles. For this testing, the ENEPIG was deposited at nominal thicknesses

of 5.38 µm [212 µin] of electroless nickel (EN), 0.081 µm [3.17 µin] of electroless palladium (EP) and 0.015 µm [0.58 µin]

of immersion gold (IG).

Note: The committee continues to be interested in any additional test data using other metals and contact shapes for this

particular application.

1.4.4 EMI Shielding ENEPIG can be used as a surface ﬁnish at the interface between electromagnetic interference (EMI)

shielding materials and printed boards (PBs).

1.4.5 Interface for Conductive and/or Anisotropic Adhesives ENEPIG is suitable for use as an interface for conductive

adhesives used as an alternative to solder. It is also suitable for anisotropic adhesive applications.

1.4.6 Connectors

1.4.6.1 Press-Fit Applications

Press-ﬁt performance for compliant pin applications should meet Telcordia GR-1217-

CORE, MIL-C-28859 or equivalent. Excessive electroless nickel thicknesses can lead to concerns with excessive press-ﬁt

insertion forces. The additional thickness of the palladium speciﬁed either by this speciﬁcation and/or a customer-speciﬁc

requirement should be added to the electroless nickel thickness ﬁt calculation when considering the type of application.

1.4.6.2 Edge Tab Contact Applications The ENEPIG surface ﬁnish is suitable for plug-to-install applications (twenty

insertions/withdrawals or less) using low insertion force (LIF) or zero insertion force (ZIF) connectors. ENEPIG is not

believed to be suitable as a surface ﬁnish for edge connectors that require multiple insertion/withdrawals (more than twenty)

or high insertion force applications. This application generally requires an alternate metallic ﬁnish, such as electrolytic hard

gold.

1.4.7 Limitations of ENEPIG

1.4.7.1 Creep Corrosion/Chemical Resistance

ENEPIG, similar to the other alternate surface ﬁnishes addressed by the

IPC-455X series speciﬁcations, is susceptible to creep corrosion in high sulfur and/or chlorine-containing atmospheres that

are commonly also at high temperature and humidity. While mixed ﬂowing gas (MFG) tests per Battelle Class 2 conditions

have been performed and show sustained solderability with ENEPIG, it is recommended to test speciﬁc design/applications

IPC-4556 January 2013