IPC-TM-650 EN 2022 试验方法.pdf - 第370页

4.26 Thermal cycling chamber for t hermal 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 …

Scope

describe the strain gage method for determin-

ing linear thermal expansion of laminated materials within the

temperature range of –55 °C to +130 °C and inorganic sub-

strates (nonlaminated) with a range of –55 °C to +150 °C.

1.1

Care

should be taken if the higher temperatures are

used. The adhesive shown is rated by the manufacturer from

less than –200 °C to greater than +300 °C; however, for

higher temperature pretesting with the Titanium Silicate Stan-

dard or materials of known thermal expansion characteristics

is recommended.

Applicable Documents

None

Test Specimens

3.1

Specimens

are normally flat pieces of laminate or printed

wiring boards/assemblies that are to be tested nondestruc-

tively. Dimensions are to be 50.0 mm x 50.0 mm [2.0 in X

2.0 in] minimum by 1.5 mm [0.060 in] minimum thick.

Plated-through holes in the specimen are not desirable, but

can be tolerated to a certain extent. If possible, the strain

gages are to be located as far from the PTHs as possible and

centered with regard to surrounding PTHs. Mounting strain

gages over PTHs will result in measurements that may not be

representative of the sample material.

For each material or lot tested, a minimum of three determi-

nations shall be made in each of the x and y directions.

Apparatus

4.1

Silicon

carbide paper, 220, 320 and 400 grit

4.2

Cotton

tipped applicator

4.3

Tweezers,

stainless steel, Style 3C

4.4

Scissors,

stainless steel, 2 to 4 inch blades

4.5

Tape,

Mylar, transparent, 1/2 inch wide

4.6 Tape,

Mylar, transparent 1 inch

4.7 Tape,

PFTE, 1 inch wide, no adhesive

4.8 Binder

clips, No. 100, large

4.9

Binder

clips, No. 20, small

4.10

Silicone

gum pad (2.5 mm [0.0984 in] thick) with metal

backup plate

4.11

Test

plate constructed of 1.25 mm [0.050 in] thick

Alloy 42 plated with 0.025 mm [0.001 in] of copper

4.12

M-Prep

Conditioner A or equivalent

4.13

M-Bond

610 Adhesive or equivalent (M-Bond 600 for

lower cure temperatures, if applicable)

4.14

M-Prep

Neutralizer 5 or equivalent

4.15

M-Coat

B, Nitrile rubber coating

4.16

Cleaning

solvent, Isopropan OL or equivalent

4.17

Strain

gages, Type WK-06-250BG, Measurements

Group Inc. (Other strain gages may be selected for customiz-

ing for a specific material or temperature range.)

4.18

Alloy

42 Holding Fixture (∝30-400 °C) = 4.5-5.0

ppm/°C

4.19

Solder

terminals, Type CEG-63S, Measurements

Group Inc. (Terminal may be integral when using WK series

strain gage with option W.)

4.20 Select

a solder that will maintain a connection at test

temperature;

Solder Sn-63/Pb-37 Liquidus = 183 °C [361 °F]

Solder Sn-96.5/Ag-3.5 Liquidus = 221 °C [430 °F]

Solder Pb-97.5/Ag-1.5/Sn-1 Liquidus = 309 °C [588 °F]

4.21

Solder

Flux, Type RMA or equivalent

4.22

Soldering

Iron, 15 to 25 watt

4.23

M-line

Rosin Solvent, Measurements Group Inc.

4.24

Oven

for Curing M-Bond Adhesive with heat rise of

3 °C to 11 °C/min [5 °F to 20 °F/min].

4.25 Gauze

Sponge

2215

Sanders Road

Northbrook, IL 60062-6135

IPC-TM-650

TEST

METHODS MANUAL

Number

2.4.41.2

Subject

Coefficient

of Thermal Expansion—Strain Gage

Method

Date

05/04

Revision

Originating Task Group

Rigid Printed Board Performance Task Group

(D-33a)

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.

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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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