IPC-TM-650 EN 2022 试验方法.pdf - 第371页

5.3.5 Place the gage/terminal assemblies in their original position over the reference lines, using only enough pressure to allow the assemblies to be tacked down. Overlay the gage/ terminal area with thin pieces of PTFE…

4.26

Thermal

cycling chamber for thermal cycling with a

heat rise capability of 2 °C to 30 °C/min [3 °F to 54 °F/min],

and equipped with a programmable temperature control sys-

tem

4.27

Thermocouple

Type J (Type may be used where appli-

cable)

4.28

Titanium

Silicate Standard

Corning Glass Works Code 7971ULE, or

Measurements Group Inc. #TSB-1

4.29

Wheatstone

Bridge

*See 6.1 for source of materials.

Strain Gage Mounting Procedure

The

procedure for

mounting the strain gages to the PCB material and titanium

silicate or other standards as appropriate, includes the prepa-

ration of the adhesive and specimen bonding surfaces, appli-

cation of the adhesive, attachment of the strain gages, and

the assembly of the Alloy 42 holding fixture. (The Alloy 42 fix-

ture may not be required, depending on specimen type and

application.)

5.1

Adhesive Preparation

The

strain gages are to be

mounted using adhesive M-Bond 610 or equivalent. The

M-bond 610 is a two-component system that is mixed as fol-

lows:

5.1.1

The resin and curing agent bottle are to be at room

temperature before opening.

5.1.2

Using

the disposable plastic funnel, empty contents of

bottle labeled ‘Curing Agent’ into the bottle of resin labeled

‘Adhesive’ (discard funnel).

5.1.3

After

tightening the brush cap (included separately),

thoroughly mix contents of the ‘Adhesive’ bottle by shaking

for 10 seconds.

5.1.4

Identify

the ‘Adhesive’ bottle by writing the date on the

label. Allow the freshly mixed adhesive to stand for a minimum

of one hour before using.

5.2

Sample Preparation

Two

strain gages are applied to

one side of the PCB board test specimen at right angles to

one another and to the titanium silicate reference standard

using the following procedure:

5.2.1

Mark

reference lines perpendicular to each other on

the test specimen and the titanium silicate standard. For most

printed board material this is easily accomplished by making a

burnish mark with the wooden end of a cotton-tipped swab

applicator.

5.2.2

Thoroughly

degrease the gaging areas with cleaning

solution.

5.2.3

Dry

abrade the area to be bonded with 220 or 320 grit

silicon carbide paper, and follow with a final with a final abrad-

ing with 320 or 400 grit paper on the areas thoroughly wetted

with M-prep Conditioner A. Scrub the gaging areas with

repeated applications of Conditioner A using a cotton tipped

swab and until a clean cotton swab or lint free pad is no

longer discolored. Remove all residues and Conditioner A by

wiping thoroughly with a gauze sponge. Do not allow to dry

while cleaning before use of the sponge to prevent the con-

taminating films.

5.2.4

Apply

a liberal amount of M-Prep Neutralizer 5 and

scrub with a cotton-tipped applicator or lint free pad. Using a

single slow wiping motion with gauze sponge, carefully dry the

surface. Do not wipe with a back and forth motion as this may

allow contaminants to be redeposited.

5.3

Strain Gage Installation

Apply

the strain gages to the

previously cleaned areas of the PCB specimen and the tita-

nium silicate standard using the following procedure:

5.3.1

Remove

the gage from the acetate envelope with

tweezers; do not bend the gages. Place the gage bond side

down onto the cleaned area of the specimen. If a solder ter-

minal is to be incorporated, position it next to the gage. Place

a short length of Mylar tape over about half of the gage tabs

and entirely over the terminals.

5.3.2

Peel

back one end of the taped assembly (by lifting at

a small angle) so as to raise both gage and terminal. By curl-

ing the Mylar tape back upon itself, it will remain in position to

be accurately relaid following the application of the adhesive.

5.3.3

Apply

the M-Bond 610 adhesive with a cap brush over

the gage surface to form a thin uniform coating. Repeat the

application technique to the specimen gage area. Do not

allow adhesive to come in contact with the tape adhesive.

5.3.4

Air

dry the assemblies for 30 to 40 minutes at 24 °C ±

2 °C [75 °F ± 4 °F] and 40 to 55% relative humidity.

IPC-TM-650

Number

2.4.41.2

Subject

Coefficient

of Thermal Expansion—Strain Gage Method

Date

05/04

Revision

age2of4

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5.3.5

Place

the gage/terminal assemblies in their original

position over the reference lines, using only enough pressure

to allow the assemblies to be tacked down. Overlay the gage/

terminal area with thin pieces of PTFE tape, and anchor them

in position with pieces of Mylar tape across the ends.

5.3.6

Cut

the silicone gum pads to size slightly larger than

the gage/terminal areas, carefully centering them in position.

Larger pads may restrict proper spreading of the adhesive

and entrap residual solvents during the curing process.

5.3.7

Use

spring clamps or dead weights to apply pressure

(275 to 350 kN/m

[40

to 50 psi]) and place in the curing oven

which is to be at room temperature.

5.3.8

Raise

the temperature to 100 °C ± 3 °C [212 °F ±

6 °F] (use 79 °C [174 °F] if using M-Bond 600) at a rate of

3 °C to 11 °C/min [5 °F to 20 °F/min], and cure for 4 1/2 to 5

hours. Air bubble entrapped in the adhesive, uneven glue

lines, and high adhesive stresses often result from starting

with a hot oven.

5.3.9

Remove

the specimens after allowing the oven to cool

below 55 °C [131 °F], remove clamps and Mylar tape, and

clean the entire surface with isopropyl alcohol to remove

residual tape adhesive. Wipe dry with a gauze sponge.

5.3.10

Post

cure for 2 to 2 1/2 hours at 40 °C [104 °F]

(30 °C [86 °F] per M-Bond instructions) above the test upper

limit temperature. Care must be taken, if base materials hav-

ing low T

values

(FR-4) are to be tested.

5.3.11

Bond

the solder tabs 6.4 mm [0.25 in] from the strain

gages. The gage leads are to looped slightly prior to soldering

to prevent inducement of strain resistance changes. Solder

tabs may be attached in the same step as the strain gages.

5.4

Specimen Fixture Preparation

(If

required, Figure 1)

5.4.1

The

PCB and titanium silicate standards, once

assembled with the strain gages, are fixtured to prevent bend-

ing or warping by the straps labeled PL in Figure 1 during the

temperature cycle test. The fixture used for the specimens will

not interfere with the thermal expansion of the specimens

being tested.

The fixture is constructed of 1.25 mm [0.050 in] thick Alloy 42

plated with 0.025 mm [0.001 in] of copper. This material was

chosen because of its thermal expansion properties that are

close to that of the test specimens. Plated Alloy 42 straps are

used to gently hold the specimen flat to the fixture. Other

materials that may closely match the CTE of the test speci-

men may be used.

5.5

Test Configuration

Connect

two strain gages, one to

the test specimen and one to the to the titanium silicate stan-

dard, in adjacent arms forming a half bridge; the remaining

half of the Wheatstone bridge being completed with the

Wheatstone bridge instrument (see Figure 2). Repeat for the

remaining two strain gages, one on the test specimen and

one on the titanium silicate standard with a second Wheat-

stone bridge instrument in the circuit.

Attach (tape) thermocouple to the sample within a 6.0 mm

[0.25 in] of the measurement area.

5.6

Specimen Conditioning/Thermal Cycling

Clean

the

specimens by immersing in M-Line solvent with agitation for

15-20 seconds. Allow to dry for 1 to 1 1/2 hours at 40 °C ±

5 °C [105 °F ± 9 °F].

5.6.1

Place

the specimens and the reference standards in

the thermal cycling chamber (with programmable temperature

control) set at 20 °C [68 °F] and allow to stabilize for 30 to 40

minutes or as required to relieve strain gage attachment

stresses.

5.6.2 Increase

temperature at a rate of 2 °C/min [3 °F/min]

up to 130 °C [266 °F] or other test temperature designated,

allowing the specimens to stabilize for 10 minutes or longer, if

IPC-24412-1

Figure

1 Test Fixture Conﬁguration

Sample

Strap 2PL

Base Plate

▼

IPC-TM-650

Number

2.4.41.2

Subject

Coefficient

of Thermal Expansion—Strain Gage Method

Date

05/04

Revision

age3of4

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required.

Decrease the temperature to –55 °C ± 2 °C [–67 °F

± 3 °F] or other temperature designated and allow to stabilize

for 10 minutes or until no further changes are noted on the

meter. Increase the temperatures to 25 °C [77 °F] at the same

rate and allow the specimens to stabilize.

5.6.3

Throughout

the thermal cycle, the temperature and

change in resistance as noted on the meter(strain) should be

recorded at the desired time and temperature (two minute

intervals).

5.7

Calculation of CTE

Plot

the gage resistance versus

the temperature. Measure the slope of the line between the

temperatures of interest and record.

The equation for calculating the Coefficient of Thermal Expan-

sion, ∝, are:

∝ = ∆R/R(GF)∆T

Where ∝ = the coefficient of thermal expansion R = gage

resistance reading

∆R = the change in resistance reading

∆T = the change in temperature

GF = the Gage Factor of a particular gage and gage con-

figuration and is furnished by the strain gagemanufacturer.

The GF for the WK gage is near 2.1

Example:

Resistance reading at 20 °C [68 °F] = 352.39

Resistance reading at 170 °C [338 °F] = 353.40

GF as furnished by manufacturer = 2.11

∝ =

(353.40 – 352.39)

(353.40

X 2.11 X 150)

= 9.03 ppm/°C

Note:

The

graph plot of ∆R/∆T will allow selection of any tem-

perature point.

All strain and temperature data should be recorded on a disk.

Software packages are available that the raw data (resistance

changes and temperature) to strain and temperature. The

software compensates for gage factor with temperature,

apparent strain of the gage, and the bridge configuration in

reducing the data. The software also uses the data from the

titanium silicate standard to adjust the reduced data of the

test specimen.

6 Notes

6.1

Suggested Sources of Materials

6.1.1

Source

of Adhesive System

Micro-Measurements Division

Measurements Group Inc.

P. O. Box 27777

Raleigh, NC 27611

Phone: (919) 365-3800

6.1.2 Information Bulletin

Micro-Measurements Division

Measurement Group Inc.

P.O. Box 27777

Raleigh, NC 27611

Phone (919) 365-3800

Bulletin # B130-10

6.1.3

Titanium

Silicate Standard

Corning Glass works

Corning, NY 14831

Micro-Measurements Division

Measurement Group Inc.

P.O. Box 27777

Raleigh, NC 27611

Phone (919) 365-3800

IPC-24412-2

Figure

2 Wheatstone Bridge Instrumentation Hookup

R Gage on Unknown

R Gage on Standard

R Standard Resistors on Instrument

M Direct Reading Strain Meter

External or Measurement

Half Bridge

Internal or Instrument

Half Bridge

IPC-TM-650

Number

2.4.41.2

Subject

Coefficient

of Thermal Expansion—Strain Gage Method

Date

05/04

Revision

age4of4

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