IPC-TM-650 EN 2022 试验方法-- - 第56页

5.4.3.1 Rough Polish Rough polish (6 - 3 µm [236 -118 µ in ]) t he s pe c im en u si n g a h a rd , l ow , or n o n a p c l ot h. Reduced wheel speeds are generally use d during final polish- ing due to the increased dra…

5.4.1 Grinding Method A

5.4.1.1 Rough Grinding

Rough grind the mount prior to

the feature intended to be evaluated with abrasive medium.

Wheel speeds of 200 to 300 rpm are generally used during

grinding.

Rotate the specimen 90° between each successive grit size

and grind for two to three times the time it takes to remove

the scratches from the previous step. The scratch removal

can be verified by microscopic inspection between steps. It is

of great importance that the ground surface of the microsec-

tion is in a single plane. The purpose of rotating the microsec-

tion 90° between successive grit sizes is to facilitate

inspection. If scratches are observed to be perpendicular to

those made during the last step performed, it is a good indi-

cation that the surface is not flat and the microsection requires

additional grinding. If the surface of the microsection is not flat

upon completion of the grinding operations, it may not be

possible to remove all of the grinding scratches during fine

grinding.

Caution: Copious water flow must be used to prevent over-

heating, damage to the specimen, and removal of grinding

debris on all grinding steps.

5.4.1.2 Fine Grinding

The final abrasive medium (ANSI

600 grit/P1200 FEPA) should finish at the axial centerline of

the intended feature to be evaluated, such as the plated

structure.

5.4.2 Grinding Method B

5.4.2.1 Tooling Stops

The mount holder has tooling stops

to allow the equipment to grind a set distance. These stops

must be calibrated for each abrasive paper grit to assure that

any scratches from the previous step are removed. See IPC-

MS-810 for a detailed discussion and examples.

5.4.2.2 Grind Pressure

The equipment’s pressure setting

is the direct force on a load cell. To determine the pressure on

each mount, divide the pressure setting by the surface area of

the mounts being processed. See IPC-MS-810 for a detailed

discussion and examples.

The recommended pressure setting for six mounts at 38.1

mm [1.5 in] diameter is 351.5 g/sq. cm (5.0 psi) with the wheel

rotation between 300 - 600 RPM.

5.4.2.3 Other Variables

Recommended variables to be

familiar with are length of time the abrasive paper removes

material efficiently, scratch size the abrasive paper causes on

the specimen(s) surface, and water quality (undissolved par-

ticles that can cause scratches; i.e., calcium deposits).

5.4.2.4 Grind the Mounts

Be liberal with the amount of

water used to promote efficient removal of material by the

abrasive paper. The hardness of the specimen will dictate the

number of rough and fine grind steps needed to reach near

the center of the hole. The rough grind grits ANSI 180-240

(P180 - P240 FEPA) are used to enter the edge of the PTH,

and the fine grind grits ANSI 400-600 (P800-P1200 FEPA) are

used to grind near the center of the hole. The distance to stop

short of the center is determined by the scratch size of the last

grind step used.

A recommended grinding process from which to start devel-

opment is provided in Table 5-2.

5.4.2.5 Clean the Mounts

Clean the mount surface with a

mild hand soap to remove the abrasive grit. This is especially

important when the same mount holder is used for grinding

and polishing. Be careful not to scratch the surfaces to be

evaluated while cleaning.

5.4.3 Polish

The diamond polish media is preferred for

printed boards. Diamond media substantially reduces the risk

of metal smear and rounding. Diamonds provide a sharper

definition of copper surfaces to evaluate for separation of con-

ductive surfaces.

IPC-211-5-2.eps

Figure 5-2 Plated Hole Microsection (Grinding/Polishing)

Tolerance

Note 1. Measurement Example with a Negative Etchback

Process

Note 2. Measurement Example with an Etchback/Desmear

Process

Note 3. Center of Hole Measurement Location

Note 4. Minimum Viewing Area Length = Drill Diameter x 0.9

Note 5. Maximum Viewing Area Length = Drill Diameter

IPC-TM-650

Number

2.1.1

Subject

Microsectioning, Manual and Semi or Automatic Method

Date

6/15

Revision

Page 4 of 8

5.4.3.1 Rough Polish

Rough polish (6 - 3 µm [236 -118

µin]) the specimen using a hard, low, or no nap cloth.

Reduced wheel speeds are generally used during final polish-

ing due to the increased drag on the microsection. Utilize rec-

ommended lubricant for each polishing medium. Following

rough polishing, microscopically examine the specimen to

verify removal of all previous grit scratches. Ultrasonically

clean the specimen, if desired.

5.4.3.2 Fine Polish

Continue polishing with 1.0 - 0.25 µm

[39.4 - 118 µin] using a hard, low, or no nap cloth and micro-

scopically examine the specimen to verify the removal of all

the previous scratches.

5.4.3.3 Method B – Polish Process Setup

The tooling

stops are recessed or removed from the mount holder during

polishing. The reason for this is that the polish process

removes a negligible amount of material and will not change

the flatness of the surface. The number of polish steps is

determined by the hardness of the specimen(s), distance to

the center of the hole, and scratch size of the last fine grind

step. There may be multiple intermediate polish steps but only

one final polish step.

5.4.3.4 Method B – Intermediate Polish Steps

The inter-

mediate steps must remove the fine grind scratches and pre-

pare the surface for the final polish step. The recommended

process settings for six mounts at 38.1 mm [1.5 in] diameter

is less than 351.5 g/sq. cm [5.0 PSI], a medium to hard pol-

ish cloth, short nap surface, and low wheel RPM (100-200).

Additional variables that must be considered are volume of

lubricant, lubricant types, abrasive size, abrasive type (dia-

mond or oxide), and process time.

5.4.3.5 Method B – Final Polish the Mounts

The final

polish step removes the scratches from intermediate polishing

and prepares the surface for evaluation. The recommended

process setting for the same surface areas as 5.4.3.4 are a

medium to soft polish cloth, low wheel RPM (100 - 200), and

Table 5-1 Suggested Grinding/Polishing Steps – Method A

1,2

2 Step

3 Step 4 Step 5 Step Grit ANSI (FEPA)

60 (P60)

Rough Grinding

80 (P80)

120 (P120)

180 (P180)

220 (P220)

240 (P280)

280 (P320)

320 (P320)

400 (P800)

Fine Grinding

600 (P1200)

800 (P2000)

1200 (P4000)

5 micron

Polish

3 micron

1 micron

0.25 Micron

Note 1. The metallographer should recognize the fact that the coarser grit sizes (180, 240, and 320) induce a larger depth of deformed and fragmented material.

Since the depth of deformation decreases sharply below a particle size of about 30.0 µm [1181 µin] (400 grit), it is better practice to spend longer times on

400 grit and especially 600 grit to achieve the final plane sectioning, rather than on the coarser grit sizes.

Note 2. The multiple step method represent ranges that can be used and any one grit size can be used per step.

Note 3. The 2 step process may be used for in-process checks but is not recommended for final acceptance of product.

Table 5-2 Recommended Grinding Process – Method B

Step 1 Step 2 Step 3

Abrasive grit size P180 P 400(opt) P1000

RPM 200-300 200-300 200-300

Pressure (g/sq.cm) 351.5 351.5 351.5

Time 15 seconds after the stops touch

IPC-TM-650

Number

2.1.1

Subject

Microsectioning, Manual and Semi or Automatic Method

Date

6/15

Revision

Page 5 of 8

low pressure setting 351.5 g/sq. cm [5.0 PSI] or less. Addi-

tional variables that must be considered are volume of lubri-

cant, type of nap surface on polish cloth, and process times.

The type of abrasive used must be diamond (maximum rated

size: 1.0 µm [39.4 µin]) or colloidal silica.

WARNING: If a high nap polish cloth is used too long in the

final polish, the inspectors ability to see defects can be ham-

pered. This step must be engineered for short process times

(30 seconds or less) with a careful balance of lubricant to pre-

vent copper rounding.

A recommended polish process from which to start develop-

ment is provided in Table 5-3.

5.4.3.6

Rinse in mild soap and warm water or IPA and blow

dry.

Caution: Do not touch or wipe surface with anything that

might cause scratches to the polished surface.

5.4.3.7

Examine and repolish, beginning with 6.0 µm [236

µin] diamond, if necessary, until:

1) There are no scratches larger than those induced by the

final polishing abrasive.

2) The specimen is not higher or lower than the mounting

material (rounding of metal surfaces).

3) There is no smearing of the copper plating into the PTH or

base material.

4) The plane of microsectioning is at the centerline of the hole

as defined by the governing specification. If the grinding

depth is insufficient, additional grinding and repolishing

may be required.

5) There is little, if any, visible preparation induced damage to

the glass fibers of the base material.

See IPC-MS-810 for photomicrographs illustrating some of

the above qualities.

5.5 Examination of Microsections

5.5.1 ‘‘As-Polished’’ Condition

When specified, examine

the microsection of multilayer printed boards in the ‘‘as-

polished’’ condition to assess attributes such as internal layer

separation (which may appear as dark lines or partial dark

lines). These areas should be documented prior to microetch-

ing and verified after metallographic etching. There may not be

a one-to-one correlation of all separations noted ‘‘as-

polished’’ versus those noted after etching, when examined at

the specified magnifications.

It is recommended to microetch immediately after the ‘‘as-

polished’’ evaluation to avoid oxidation.

5.5.2 Microetched Condition

Caution: Over etching may totally obscure the demarcation

line between the copper foil and electroplated copper, pre-

venting accurate inspection.

5.5.2.1

Prepare a small volume of copper etch solution

such that:

a) (no more than 10ml) containing 50/50 v/v of ammonium

hydroxide (nominally 28%; grade is not defined) and stabi-

lized hydrogen peroxide (nominally 3%; grade is not

defined). This is the most active concentration and will last

about one hour.

Note: Hydrogen peroxide solution is light sensitive and

should be stored in an opaque container.

b) The addition of 25 ml of water (distilled or reverse osmosis)

will dilute the solution, resulting in longer etching times,

which may be desirable in certain situations. This concen-

tration will have to be remade with each batch.

5.5.2.2

Expose the surface of the microsection to the etch

solution by using one of the following methods:

a) Swab

1) Apply etchant to a swab (outcome based control: no

nonconforming scratches caused by swab).

Table 5-3 Recommended Polishing Process - Method B

Intermediate Final Optional

Type of cloth Napless Napless Nap

Type of polish

abrasive

Diamond Diamond Diamond

Polish

abrasive size

3.0 µm

[118 µin]

1.0 µm

[39.4 µin]

1.0 µm

[39.4 µin]

Time — — 30 sec max.

Pressure

(g/sq. cm)

[PSI]

351.5

[5.0 psi] or

less

351.5

[5.0 psi] or

less

351.5

[5.0 psi] or

less

Note 1. When inspecting for innerlayer separations, the optional polish step

shall not be used (see 6.2).

Note 2. Generally, polishing using medium pressure during the above steps is

sufficient if the microsection has been ground correctly. This final

step is only performed for 10 - 20 seconds using light to medium

pressure when using oxide or silica polishing compounds. When

using diamond compounds on soft woven cloths, final polishing may

extend several minutes (see 6.3).

IPC-TM-650

Number

2.1.1

Subject

Microsectioning, Manual and Semi or Automatic Method

Date

6/15

Revision

Page 6 of 8