IPC-TM-650 EN 2022 试验方法--.pdf - 第55页

5.4.1 G rind i ng Method A 5.4.1.1 Rough Grinding Rough grind the mount prior to the feature intended to be evaluated with abr asiv e me dium. Wheel speeds of 200 to 300 rpm are g enerally used d uring grinding. Rotate t…

use of double-sided adhesive tape. Keep sample in center of

mount mold.

5.3.3.2 Method B

Load specimen on tooling pins. The pins

align the target PTHs on a common plane. This common

plane assures all the PTHs will grind to the center of the hole

at the same instance.

Push the tooling pins into the tooling holes or slots. The pins

must fit snugly.

5.3.4 Preparing Potting Material

Personal protection is

recommended to prevent skin sensitization. Prepare potting

material to ensure cure temperature does not exceed 93 °C

[200 °F]. Mix by folding the potting material in such a way so

as to minimize air bubbles.

5.3.5 Pouring Potting Material

Fill the mount mold care-

fully with potting material, by pouring from one side to ensure

adhesion to all sample surfaces.

5.3.5.1 Method A

The sample must remain upright while

pouring.

5.3.5.2 Method B

Assure the tooling pins do not shift

position or rise up while pouring and/or curing of the potting

material.

5.3.6 Removal of Vacuum or Pressure for Potting Mate-

rials

While in a liquid state, potting materials may require

vacuum or pressure in order to achieve proper encapsulation.

Remove vacuum or pressure prior to cure to prevent undue

stress on the specimen.

5.3.7 Cure and Mount Removal

Allow specimen to cure

and cool to room temperature before removing hardened

mount from mount mold. The minimum qualities the mount

should exhibit are:

• The potting material is hard and not tacky.

• Minimal bubbles in the potting material.

• No gaps between the potting material and the sample.

• All gaps in structure to be evaluated should be filled with

potting material.

The presence of these deficiencies will result in sample prepa-

ration difficulties, as noted in 5.3.2.

5.3.8 Marking of Specimen

Identify the specimen by a

permanent method (see 4.22). The selected marking system

should remain unaffected by subsequent processing.

5.3.9 Mount Preparation

5.3.9.1 Method A

Remove sharp edges and flatten top

with low grit (240) sand paper.

5.3.9.2 Method B

Remove the excess mounting material

from the exposed ends of pins.

5.4 Grinding and Polishing

The following is a description

of the basic grinding and polishing steps. Other methods may

be required by contract. See Table 5-1 for examples of 2, 3,

4, and 5-step methods for Method A and Table 5-2 and Table

5-3 for Method B.

The minimum qualities the mount shall exhibit are:

1) The grinding and polishing accuracy of the microsection

shall be such that the viewing area of each of the PTHs is

within 10% of the drilled diameter of the hole as shown in

Figure 5-2.

2) Only fine grind scratches apparent on the mount when

viewed at 100X magnification.

3) Little or no gap between the potting material and the

specimen(s).

4) No residual abrasive paper grit material on the mount

surface.

5) The ground surface has only one plane of material removal.

If the mount has several planes of material removal, por-

tions of the sample will not polish since the odd surface

never touches the polishing cloth.

Note: Ultrasonic cleaning is highly recommended, especially

between the finer grinding steps, prior to rough polishing and

between all polishing steps. It is the nature of printed board

specimens, especially those with epoxy base material follow-

ing thermal exposures, to contain voids that can trap grinding

and polishing residues that are not removed during simple

rinsing. Care needs to be exercised not to damage the speci-

men surface with excessive ultrasonic cleaning. Specimen

sample can be placed with the polished surface perpendicu-

lar to the bottom of the vessel. Ultrasonic cleaning for as little

as one minute can damage a polished surface.

IPC-TM-650

Number

2.1.1

Subject

Microsectioning, Manual and Semi or Automatic Method

Date

6/15

Revision

Page 3 of 8

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