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SEMI G48-89 © SEMI 1989, 1996 4 mark (either eject or pin or Pin # 1 indicator or other feature). 5.13.3 The indicato r is set to zero on the package surface and then moved to th e bottom of the feature. The readout is r…
SEMI G48-89 © SEMI 1989, 1996 3
Centerline of Package = (T2 + T1)/2; (B2 + B1)/2.
(Relative to datum)
NOTE: Figure 2 calculations assume that the leadframe
centerline is equidistant between T3 and the zero datum point.
5.4.5 In lieu of the frame pilot hole, the dambar may be
used on the frame when measuring the offset; however,
the possibility of tolerance error may become
cumulative, particularly with etched rather than
stamped frames.
NOTE: By SEMI convention the offsets are defined in
relation to the bottom cavity of the mold.
5.5 Top Cavity Length “Y” Axis — (Figure 2)
5.5.1 Equipment — Toolmaker’s Microscope at 30×.
5.5.2 Focus the microscope on the leadframe datum
point. Zero the digital readout. Move the stage to the
intersection of the mold compound and the leadframe
parting line. Read and record. Continue to measure
across the package length to the intersection of the
mold compound and the leadframe parting line on the
opposite edge of the package. Read and record.
5.5.3 The cavity length is defined as (Ty2 – Ty1).
5.6 Top Cavity Width “X” Axis — (Figure 2)
5.6.1 Equipment — Toolmaker’s Microscope at 30×.
5.6.2 Focus the microscope on the leadframe datum
point. Zero the digital readout. Move the stage to the
intersection of the mold compound and the leadframe
parting line. Read and record the reading. Continue on
to the intersection of the mold compound and the
leadframe parting line on the opposite side. Read and
record.
5.6.3 The cavity width is defined as Tx2 – Tx1.
5.7 Bottom Cavity Length “X” Axis — (Figure 2)
5.7.1 Equipment — Toolmaker’s Microscope at 30×.
5.7.2 Focus the microscope on the same datum point
used for the top cavity length (remember the package
has been turned over). Zero the digital readout. Move to
the intersection of the mold compound and the
leadframe parting line. Read and record the reading.
Continue to the intersection of the mold compound and
the leadframe parting line on the opposite side. Read
and record. The bottom cavity length is the difference
of the two readings. Record the bottom cavity length
(By2 – By1).
5.8 Bottom Cavity Width “X” Axis — (Figure 2)
5.8.1 Equipment — Toolmaker’s Microscope at 30×.
5.8.2 Focus the microscope on the leadframe datum
point. Zero the digital readout. Move the stage to the
intersection of the mold compound and the leadframe
parting line. Read and record. The bottom cavity width
is the difference of the two readings (Bx2 – Bx1).
5.9 Cavity Overlap/Underlap — (Figure 4)
5.9.1 Compare the top cavity length to the bottom
cavity length and the top cavity width to the bottom
cavity width. The difference in the number is the
overlap/underlap for each axis.
5.10 Cavity to Cavity Mismatch — (Figure 2)
5.10.1 The comparison of the centerlines of the top
cavity length to the bottom cavity length and the top
cavity width to the bottom cavity width shall determine
the cavity to cavity mismatch.
Formula:
Cavity to Cavity Mismatch =
(B2 + B1)/2 – (T2 + T1)/2
5.11 Cavity Depth — (Figure 1)
5.11.1 Equipment — Depth Indicator
5.11.2 Top Cavity Depth — Measure the distance from
the top surface of the leadframe to the top of the unit,
place the indicator on the surface of the leadframe,
zeroing the readout, moving the part to a point where
the top of the unit can be indicated, and read and record
the readout.
5.11.3 Bottom Cavity Depth — The measurement is
performed in the same manner as the measurement in
Section 5.11.2 except the part is turned over and the
bottom surface of the leadframe to the bottom of the
unit is used.
5.11.4 The package depth is the sum of the frame
thickness and the top and bottom depth. (This
measurement should equal Section 5.1. Any variation
may be considered measurement error.)
5.12 Molding Protrusions Top/Bottom of Part —
(Figure 3)
5.12.1 Equipment — Digital depth indicator.
5.12.2 Place unit on the anvil and zero the indicator on
the package surface away from area of protrusion.
Carefully move the part to where the protrusion is
located. Carefully lower the indicator to the top of the
mold protrusion. Read and record the mold protrusion.
5.13 Pin Depths — (Figure 3)
5.13.1 Equipment — Depth indicator with a fine point
or “Z” axis reading toolmaker’s microscope.
5.13.2 The measurement is made from the nominal
plane of the package surface to the bottom of the design
SEMI G48-89 © SEMI 1989, 1996 4
mark (either ejector pin or Pin #1 indicator or other
feature).
5.13.3 The indicator is set to zero on the package
surface and then moved to the bottom of the feature.
The readout is read and recorded.
5.14 Dambar Trimming Defects — (Figure 4)
5.14.1 Equipment — Toolmaker’s Microscope
5.14.2 Measure from the edge of the lead to the edge of
the protrusion or intrusion; record the reading and the
lead number.
NOTE: Dambar trimming defects are those which can be
caused by overcutting into the lead shoulder (stand off) i.e.
cutting too much or undercutting the dambar, leaving too
much dambar or a burr. Overcutting causes shoulder
intrusions. Undercutting leaves shoulder protrusions. In some
cases, an adjacent protrusion and intrusion is caused by
misalignment of the part at the time of dambar removal.
5.15 Package Warpage — (Figure 5)
5.15.1 Equipment — Microscope “Z” Axis reading
40×.
5.15.2 With the package sitting on the stage, obtain a
two point datum by measuring two-points on opposite
edges 0.005 from the radius readings; move to the
center of the package and obtain the deviation from the
datum, and read and record the reading as the warp.
5.15.3 For quad packages, it is equally important that
there be minimum warp in each axis (X or Y) so that a
three-point Z axis datum must be obtained; the two
used in 5.15.2 and an additional one, on one adjacent
edge.
5.16 Lead Coplanarity
NOTE: Applies to all surface mount devices.
5.16.1 Contact Method — (Figure 6)
NOTE: Not recommended for gull-wing leads.
5.16.1.1 Equipment
Dial Indicator 0.0001" Accuracy, 5 grams maximum
pressure.
Granite Flat.
Transfer Stand.
Package Holding Fixture.
Reference Gauge Blocks, 0.0002" Accuracy.
5.16.1.2 Place the package on holding fixture so that
the flat sections of the leads, as they exit from the
plastic, are on the ground flats of the fixture. The leads
are to be facing “UP” (Dead Bug).
5.16.1.3 On the granite flat, set up the dial indicator on
its transfer stand and zero the reading using the
reference block. Use a suitable reference block so that
all measurements are positive to avoid confusion.
5.16.1.4 Measure the highest point on each lead (e.g.,
the tangent point of a “J” lead).
5.16.1.5 Determine the range of readings.
NOTE: Special Precautions
1. Be sure that the flat of the leadframe, as it exits
from the plastic, rests on the flats of the holding
fixture. If the radiused section supports the package,
then spurious readings will result.
2. The pressure exerted by the dial indicator must not
exceed 5 grams. To check the contact pressure of
the dial indicator, use a gram gauge. The gram
pressure must be noted at the initial deflection of the
gauge and at the maximum deflection of the gauge.
If the initial deflection is greater than 5 grams, then
the point where 5 grams is obtained must be noted
and the measurement must stay within this range to
be valid.
5.16.2 Comparator/Mirror Method
5.16.2.1 Equipment — Optical comparator with at least
20× magnification as per Section 3.1.2. Mirror, flat
within 0.0005 inch with a mirror finish having the
reflective suface on top. (A polished silver wafer is
suggested.)
5.16.2.2 Place the mirror on the measurement stage
mirrored side up with the mirror in the plane of the XY
axis. Place the package on the mirror with the leads
down. Sufficient mirror must extend past the leads
toward the lens of the comparator so that an image of
the leads with its reflection can be viewed. Focus on the
leads nearest the lens. (Care must be taken not to focus
on the leads on the opposite side of the package.) (See
Figure 8.)
5.16.2.3 Measure the distance between the lead tip and
its reflection. Divide that measurement by two to obtain
the coplanarity of the lead.
5.16.2.4 Repeat for each lead. Rotate part to measure
all sides. Determine co-planarity by identifying
maximum measurement.
5.17 Shoulder Bend Location — (Figures 1, 7, and 7a)
NOTE: This measurement is not precise, since radius tangent
locations allow for considerable inspector interpretation.
5.17.1 Equipment — Comparator at 20× magnifica-
tion. (Surface and shadow illumination).
SEMI G48-89 © SEMI 1989, 1996 5
5.17.2 The measurement is made from the intersection
of the straight part of the shoulder with the shoulder
bend radius of the lead on one side of the package to the
same point on the lead on the opposite side of the
package. Locate this point on the first lead by lining up
the vertical comparator cross hair with the straight of
the lead. Bring the center point of the cross hair to this
intersection. Zero the readout, move to the opposite
lead, and repeat the location of the intersection. Record
the measurement.
NOTE: Due to shadowing of leads, only the end leads on the
package can be measured. A visual check with a 10 to 20×
microscope should be made to check for gross difference of
other leads.
5.18 Surface Finish
5.18.1 Comparative Method — (EDM Finishes only)
5.18.1.1 Equipment — Charmille Standard Surface
Gauge Binocular Microscope and Light.
5.18.1.2 Insert gauge and molded package to be
checked into a holder so that both can be viewed at the
same time under the microscope.
5.18.1.3 Estimate the surface finish on the package.
5.18.2 Absolute Method
5.18.2.1 Equipment — Automatic Surface Analyzer
Surface Standards.
5.18.2.2 Calibrate the analyzer using the gauges.
5.18.2.3 Measure the surface finish on the package.
The analyzer gives the average roughness (R
a
) and the
actual surface roughness. Use average roughness for
acceptance.
5.18.3 Table of approximate equivalent finishes
Mirror
Satin
Extra
Fine
Fine
Medium
Course
Micro
Inches
4 30 ± 10 50 ± 10 75 ± 10 105 ± 10 145 ± 10
Charmilles N/A N/A 18–21 21–24 24–27 27–30
Microns N/A 1 1.5 2 2.5 3.5
5.19 Radii
5.19.1 Comparative Method
5.19.1.1 Equipment — Optical comparator at 20×.
5.19.1.2 Radii are measured by comparison to known
radius overlays marked at the same magnification as the
comparator.
5.19.2 Absolute Method
5.19.2.1 Equipment — Toolmaker’s Microscope.
5.19.2.2 Radii are measured using the reticle lines and
the X and Y axes to obtain the radius.
5.19.2.3 Care must be taken to assure that each radius
is measured separately.
5.20 Lead Position
NOTE: Lead position is a combination of pitch variations due
to lead movement after forming and lead width. If the lead is
to fit a solder pad or hole, the combination must be
considered. In some cases, the lead width can be a major
contributor to poor lead position, eg. SO packages with gull-
wing leads, PCC with J bend.
5.20.1 Comparative Method
NOTE: This method will only determine if the part is usable,
not the breakdown of width and pitch variations.
5.20.1.1 Equipment — Optical Comparator at 20×.
5.20.1.2 Align the package to an overlay displaying
limit lines for lead pitch/width.
5.20.2 Absolute Method
5.20.2.1 Equipment — Toolmaker’s Microscope.
5.20.2.2 Move to the edge of the lead number and zero
the readout.
NOTE: Where there is a definitive end to the lead as in the
case of SO, SIP and DP, the end of the lead at the intersection
of the lead in feature, will be the measurement point. Quad
PCC packages will be measured at the top of the “J” bend
when in the “Dead Bug” position.
5.20.2.3 Move to the opposite edge of that lead and
record width.
5.20.2.4 Move to the first edge of the next lead. Record
the measurement. Repeat the width measurements.
5.20.2.5 Repeat for all leads to be measured.
5.20.2.6 Pitch can be calculated from the
measurements.
5.21 Draft Angles
5.21.1 Package Sides
5.21.1.1 Equipment — Optical comparator at 10x.
5.21.1.2 Lay the top or bottom surface of the package
squarely onto the comparator to insure that no
protrusions on the surface cause the package to be
tilted. Align the horizontal cross-hair to the leadframe.
Using the vertical cross hair, compare the draft angles
to an overlay.
NOTE: This measurement should be taken before the leads
are formed.
5.21.1.3 Repeat the procedure for all sides of the
package.