IPC-TM-650 EN 2022 试验方法.pdf - 第220页

A Certified Reference Material (CRM) covering the measuring range of the application as described in 5.2. A typical instrument layout is shown in Figure 1. IPC-2344-1 Figure 1 XRF Instrument Layout IPC-TM-650 Number 2.3.…

1 Scope The purpose of this test method is to measure the

thickness and phosphorous (P) concentration of chemically

(electroless) deposited nickel (Ni) coatings by (energy disper-

sive) X-ray fluorescence (XRF) analysis.

The measurement is nondestructive and noncontact, and can

be performed either in ambient atmosphere or under vacuum.

Measurements shall be made on a defined feature (equi-

valent to a typical SMT pad) of 1.5 mm x 1.5 mm [0.060 in x

0.060 in] or equivalent area, using a 0.6 mm diameter collima-

tor. This equates to a measuring spot size (analysis area) of

1 mm diameter.

This test method is designed primarily for failure analysis, pro-

cess qualification and process auditing. It is not intended for

daily production control, due to the complexity and cost of the

equipment required.

2 Applicable Documents

IPC-4556

Specification for Electroless Nickel/Electroless

Palladium/Immersion Gold (ENEPIG) Plating for Printed Circuit

Boards

IPC-4552 Specification for Electroless Nickel/Immersion

Gold (ENIG) Plating for Printed Circuit Boards

3 Test Specimen This test method is primarily designed

for measurement of the phosphorus content in ‘‘as plated’’

ENIG PWBs. Other ENIG or electroless nickel (EN) plated sub-

strate materials may also be tested using this method, includ-

ing flexible circuits, silicon wafers, aluminum or steel. The typi-

cal thickness range of the NiP layer on PWB substrates is 3 to

6 µm [118.1 to 236.2 µin]. The Phosphorous content can

range from0%to14%byweight. Minimum and maximum

thickness for single layers of electroless nickel required for

accurate determination of the P content is 0.5 µm to 25 µm

[19.7 µin to 984 µin]. The maximum thickness of gold present

on the surface of the specimen when tested shall be less

than 0.10 µm [0.004 µin]. For samples with thicker gold, the

gold must be removed by chemical stripping or Ion milling

prior to evaluation.

While this test method is also suitable for evaluating phospho-

rus content in ENEPIG samples, the thickness of both the

gold (Au) and palladium (Pd) layers needs to be considered.

The maximum thicknesses of the layers over the electroless

nickel on ENEPIG specimens when tested shall not exceed

0.05 µm [0.002 µin] of Au and 0.10 µm [0.004 µin] of Pd on

top of the EN layer. This constraint will impact measurement

of ENEPIG samples plated on the higher side of the current

IPC-4556 specification. For samples with gold thicknesses

above 0.05 µm [0.002 µin], chemical or Ion milling stripping

may be carried out prior to evaluation. With the gold removed,

the maximum thickness of palladium on a specimen when

tested shall be 0.25 µm [0.0098 µin].

Note: Electroless palladium deposits may also contain phos-

phorus and its contribution to the total phosphorus content

must be taken into account when reporting the phosphorus

content of the deposit.

The sample to be tested should be flat and ideally not popu-

lated with components in the area of measurement. If testing

is done on populated boards, consideration has to be given to

measurement location, such that none of the electronic com-

ponents block the fluorescent radiation from reaching the

detector, as described in Section 5.4.

The test specimen requires no other sample preparation.

4 Apparatus An X-ray fluorescence spectrometer consist-

ing of the following:

• A radiation source (X-ray tube with adjustable HV power

supply from 10 kV to 50 kV).

• A primary beam filter and safety shutter assembly.

• A video camera.

• An X-ray collimator or a polycapillary X-ray optic.

• An energy dispersive Silicon Drift Detector SDD (a device in

which charge carriers created by the incidence of X-ray pho-

tons on a high purity silicon substrate are directed to a mea-

suring electrode by an applied transverse electric field),

including electronics.

• Evaluation software capable of simultaneously measuring

coating thickness and composition of multiple layers. The

software of the instrument shall have the capability of mul-

tiple excitation modes. It is necessary to apply different exci-

tation conditions; a soft excitation for the excitation of P-K at

10 kV and a hard excitation for Ni-K at 50 kV.

• A programmable X-Y positioning stage (accurate positioning

is required especially if small areas are to be analyzed).

• The instrument must be able to record the Intensities of the

individual radiation components of the Phosphorous K

energy line (I

P-K

) and the Nickel K energy line (I

Ni-K

) with suf-

ficient precision.

3000 Lakeside Drive, Suite 105N

Bannockburn, IL 60015-1249

IPC-TM-650

TEST METHODS MANUAL

Number

2.3.44

Subject

Determination of Thickness and Phosphorus

Content in Electroless Nickel (EN) Layers by X-Ray

Fluorescence (XRF) Spectrometry

Date

03/16

Revision

Originating Task Group

Plating Processes Subcommittee (4-14)

Material in this Test Methods Manual was voluntarily established by Technical Committees of IPC. This material is advisory only

and its use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by IPC.

Page1of4

A Certified Reference Material (CRM) covering the measuring

range of the application as described in 5.2.

A typical instrument layout is shown in Figure 1.

IPC-2344-1

Figure 1 XRF Instrument Layout

IPC-TM-650

Number

2.3.44

Subject

Determination of Thickness and Phosphorus Content in

Electroless Nickel (EN) Layers by X-Ray Fluorescence (XRF)

Spectrometry

Date

03/16

Revision

Page2of4

5 Procedure

5.1 Instrument Setup

Prior to the purchase of the Certi-

fied Reference Materials (CRMs), confirm with the XRF

manufacturer that the instrument is capable of measuring

phosphorus content and obtain details of the recommended

machine set-up and operational procedures.

Instrument setups usually contain a product file that contains

the required measurement specific hardware and software

settings for the application. In addition, the product file con-

tains a calibration file which defines the calibration settings

and certified reference material to be used.

5.2 Typical Instrument setup conditions and measuring

ranges are as follows:

• Aperture Size: 1 mm for both 10kV and 50kV applications.

• Anode Current (I): I=1 mA for 10kV and I=0.15 mA for 50kV

(Anode current setup maximizing achievable instrument

count rates will yield best instrument repeatability, reference

5.3).

• Primary Beam Filter: NO filter for 10 kV and Ni Filter for

50 kV.

• Measurement Time: 120 s for 10kV and 20 s for 50kV.

5.3 Instrument Calibration Calibration shall be per-

formed with CRM’s according to the instrument manufacturer

instructions. The CRM’s shall be traceable to national labora-

tories. The structure of the reference material shall be similar

to the samples under investigation, i.e., NiP/Cu/PCB, Au/NiP/

Cu/PCB or Au/Pd/NiP/Cu/PCB. Individual calibration foils

shall not be used for multilayer coatings. The certified refer-

ence standards shall have compositions and thicknesses

similar to the samples to be measured. If desired, it is possible

to calibrate an instrument over the full (low to high) phospho-

rous range. However, optimum accuracy can be achieved by

calibrating each phosphorous range (low, mid, and high)

separately. Each phosphorous content range should be cali-

brated with no less than 4 standards per range. No less than

3 measurements per calibration standard shall be performed.

Calibration checks should be performed after each calibration

and periodically by re-measuring the calibration standards. If

the results are within the measurement uncertainty of the

standards and the uncertainty of the measurement itself, no

action is required. If not, a recalibration of the instrument is

required. Typical CRM standards used and results obtained

are summarized in Table 1.

5.4 Sample Placement There are some basic rules for

positioning specimens. For each measurement, it shall be

ensured that the X-ray fluorescence radiation can reach the

detector without obstruction. For flat, unpopulated PCB

boards, this is not a problem.

If populated boards are being measured, the operator shall

note the position of the detector and position the sample such

that no components are present in locations that would

prevent the radiation emanating from the measurement loca-

tion from reaching the detector, as illustrated schematically in

Figure 2.

The area measured should be flat and not tilted.

5.5 Measurement XRF equipment operation is instrument

specific and shall be in accordance with the instrument

manufacturer’s instructions. Always ensure that the correct

measurement file is selected for the application to be mea-

sured. Typically, instruments will slide the measuring stage out

of the instrument when the measurement chamber is opened.

The test sample is then positioned on the programmable X-Y

stage such that the laser pointer points at the measurement

location. When the measurement chamber is closed, the

stage will automatically retract into the chamber.

IPC-2344-2

Figure 2 Sample Placement with Respect to Detector

IPC-TM-650

Number

2.3.44

Subject

Determination of Thickness and Phosphorus Content in

Electroless Nickel (EN) Layers by X-Ray Fluorescence (XRF)

Spectrometry

Date

03/16

Revision

Page3of4