IPC-4552.pdf - 第7页
IPC-4552 Proposal June 2001 3.2 3.2.1 3.2.2 3.3 3.4 3.5 3.6 3.7 3.8 Finish Thickness Thickness of the ni ckel and gol d layers shal l be measured and veri fied followi ng the ENIG plat ing step in the PWB fabrication pro…
IPC-4552 Proposal June 2001
3.2
3.2.1
3.2.2
3.3
3.4
3.5
3.6
3.7
3.8
Finish Thickness
Thickness of the nickel and gold layers shall be measured and verified following the ENIG plating step in the PWB
fabrication process. The use of X-ray fluorescence methodology for thickness determination shall be in accordance
with APPENDIX 4 of this document and shall employ X-ray fluorescence (XRF) instrumentation equipped with
software and hardware specific for ENIG measurement. The XRF test method is per ISO-4527, Auto-Catalytic
Nickel-Phosphorous Coatings; Specifications and Test Methods.
Electroless Nickel Thickness
The electroless nickel thickness shall be 3 to 6 µm [118.1 to 236.2 µin].
Immersion Gold Thickness
The minimum immersion gold thickness shall be 0.05 µm [1.97 µin] at four sigma (standard deviation) below the
mean; the typical range is 0.075 to 0.125 µm [2.955 to 4.925 µin]. Higher gold thickness would normally require
extended solution dwell time and /or increased solution temperature. This can increase the risk of compromising the
integrity of the nickel undercoat due to excessive corrosion. Setup and measurement methodologies are crucial for
accuracy (see APPENDIX 4 for recommended measurement techniques).
Porosity
The ENIG immersion gold layer is not totally impervious and it will not pass the requirements of a ‘classic’ porosity
test (Nitric acid per ASTM B 735).
Adhesion
The purpose of adhesion testing for ENIG finished boards is two fold. The first is for testing the plating adhesion of
the immersion gold to the nickel as well as the nickel to the underlying metals. The second is for testing the
adhesion of the solder mask to both traces and laminate. In both cases testing should be conducted on regions of
high density on the board such as BGA sites, dams between fine pitch leaded devices or over areas of high trace
density. The tape testing will be in accordance with IPC-TM-650, test method 2.4.1 using a strip of pressure
sensitive tape. There shall be no evidence of any portion of the surface finish or the soldermask being removed, as
shown by particles of plating/pattern or soldermask adhering to the tape.
If overhanging metal (slivers) or soldermask undercut breaks off and adheres to the tape, it is evidence of overhang
or slivers, but not of adhesion failures.
Because of the requirement to test in high density areas, the potential to leave tape residue that could interfere with
soldering exists, especially if the wrong type of tape is used. Verification of zero impact to solderability must be
demonstrated for the areas tested.
Solderability
This thickness specification contained herein shall meet the coating durability requirements of Category 3 in J-STD-
003, i.e. greater than 6 months shelf life. Note: the use of steam aging (conditioning) is not an applicable accelerated
aging (stress) test method for ENIG.
Cleanliness
The ENIG finish typically will result in a surface that is cleaner than most other surface finishes. The process shall
be installed and maintained using IPC-TM-650, Test Method 2.3.25 Detection and Measurement of Ionizable
Surface Contaminants by Resistivity of Solvent Extract, and shall meet the values given in IPC-6011 series of 1.56
µg/cm
2
NaCl equivalent. Failure to meet this cleanliness specification should trigger immediate corrective action.
Chemical Resistance
Chemical resistance testing of the ENIG finish is not applicable.
High Frequency Signal Loss
Higher frequency (>1 GHz) applications may experience signal loss due to increase electrical resistance (skin
effect). Due to electrical differences such as this, special considerations should incorporated for any edge-coupled
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IPC-4552 Proposal June 2001
structures on the outer layers. This impact will be more prevalent when ENIG is applied over all copper
f
eatures,
such as application of ENIG before solder mask. This impact is minimized when only the pads (not the traces) are
plated with the finish.
4
QUALITY ASSURANCE PROVISIONS
General Quality Assurance Provisions are specified in IPC-6011 and each sectional specification. Additional
requirements for PWB with electroless nickel/immersion gold (ENIG) plating are specified herein for qualification,
acceptance and quality conformance.
4.1
4.1.1
Qualification
Qualification of a PWB product is agreed upon by the user and supplier (see IPC-6011). The process capability of a
supplier of PWB with ENIG finish shall be evaluated. APPENDIX 3 describes recommended qualification aspects
of the ENIG process by a PWB supplier.
Sample Test Coupons
Test specimens used for qualification of PWB with ENIG finish shall be as specified in IPC-2221 and each sectional
specification. Specimen for additional testing requirements is listed in Table 4-1.
Table 4-1: Qualification Test Coupons
Test Type 1 Types 2,3,5 Types 4,6 Board
Physical Requirements
Plating Thickness M2, M5 M2, M5 M2, M5 X
IPC-2221 Test Speciman M, surface mount solderability testing, mm [in]
{EvaCombes: Please note, this drawing is designated IPC-2221-12-17}
4.2
4.3
Acceptance Tests
The sampling plan and frequency of acceptance testing except the solderability and plating thickness inspections
shall be in accordance with IPC-6011 and each sectional specification. The sampling plan of the solderability and
thickness of ENIG finish shall be as agreed upon by the user and the supplier (AABUS).
Quality Conformance Testing
Quality conformance testing shall consist of inspections as specified in IPC-6011 and each sectional specification,
with the addition of regular thickness inspections. The frequency of thickness inspection shall be 1 inspection (5
XRF measurements) per lot for Class 1 and 2, and as agreed upon by the user and the supplier (AABUS) for Class 3
products.
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