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SEMI G45-93 © SEMI 198 6, 1993 2 5.3 At the beginning of each series o f tests and at each change of co mpound, check and s et t he transfer pressure us ing the force gauge. The proper force gaug e setting can be determi…

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SEMI G45-93 © SEMI 1986, 19931
SEMI G45-93
RECOMMENDED PRACTICE FOR FLASH CHARACTERISTICS OF
THERMOSETTING MOLDING COMPOUNDS
1 Scope
This method describes a procedure for measuring the
flashing characteristics of semiconductor grade transfer
molding compounds.
2 Significance
2.1 The flashing tendency for semiconductor grade
molding compounds depends on the interaction of
several variables, including mold conditions, process
parameters, molding compound viscosity, and curing
characteristics. This test is not a valid method for
predicting the flashing performance in all mold types. It
is a method for comparing flash tendency and flashing
type of different molding compounds when evaluated
under a specific set of molding process parameters.
2.2 Flashing presents problems with subsequent
processing of plastic packaged devices after molding. A
high flashing tendency increases die wear in the trim
and form operation, may interfere with plating or solder
dip finishing operations, and may prevent good contact
for electrical test. Thus, reduced tendency toward
flashing will improve the plastic package subassembly
operations. The information from this test will be of
value in rating flash performance of any given
compound to that in production use.
3 Apparatus
3.1 Transfer molding press with a platen area
sufficient to maintain a uniform mold temperature and
having (1) a transfer piston pressure potential of 1000
psi on the material; (2) sufficient clamping pressure to
prevent flashing of the molding compound at clamping
lands; and (3) a minimum plunger speed of 25.4 mm (1
inch) per second without load. The pot diameter shall
be 31.75 to 44.45 ± 0.735 mm (1.250 to 1.750 ± 0.025
inch) and the clearance between pot and ram shall be
sufficiently small that flashing does not occur above the
first sealing groove on the ram.
3.2 Standard Flash Test Mold — Per Figure 1.
3.3 Force Gauge — With appropriate range to
calibrate transfer pressure to minimum of 10.343 mpa
(1,500 psi).
3.4 Steel Rule — Measured in 0.25 mm (0.010 in).
3.5 Halo Lamp — 3× magnification, minimum.
3.6 Thermocouple and/or Pyrometer Calibrated — In
the 160°–190°C range (calibration to be checked every
6 months).
4 Test Conditions
4.1 Molding Compounds — Refrigerated shipment
and storage of some molding compounds is necessary.
The molding compound is to be at room temperature
before the container is opened. Care must be taken to
preserve the original moisture content. The material
should be in powdered form, unless otherwise
specified.
4.2 Flash Test Mold — Shall be clean and free from
any mold release agents or lubricants. A standard mold
cleaning compound can be used to insure mold
cleanliness.
4.3 Molding Conditions
4.3.1 The temperature of the mold shall be measured
using a thermocouple inserted in the mold or with a
surface pyrometer. The ram shall be kept at the mold
temperature. Molding temperature is to be 175°C unless
otherwise specified. Temperature must be maintained
within ± 3°C (± 5°F) of the specified temperature.
4.3.2 The transfer pressure for test, as measured under
the transfer plunger, is to be 6.895 ± 0.177 mpa (1000 ±
25 psi) unless otherwise specified.
4.3.3 The weight of the charge shall be adjusted to
give a molded cull thickness of 3.303 ± 0.254 mm
(0.130 ± 0.010") excluding vertical flash.
4.3.4 The free running ram speed shall be at least 25.4
mm/sec (1"/sec). Recommended speed is 100 ± 25
mm/sec into the pot and application of pressure on the
charge shall be maintained throughout the mold cycle.
4.3.5 Unless otherwise specified, a minimum of 1.5
minutes close and cure time shall be used.
4.3.6 Flash length shall be measured in 0.25 mm
(0.010 in) intervals.
5 Procedure
5.1 Thoroughly clean the ram, pot, and mold of any
cured compound, or other foreign matter.
5.2 Heat the mold and ram to within ± 3°C of the
specified temperature.
SEMI G45-93 © SEMI 1986, 1993 2
5.3 At the beginning of each series of tests and at each
change of compound, check and set the transfer
pressure using the force gauge. The proper force gauge
setting can be determined from the formula:
F=
ΠD
2
P
4
where F is the force in pounds, P is the desired pressure
on the material in psi, and D is the ram diameter in
inches.
5.4
For each material change, make at least three clean
out runs using the material to be tested before recording
data. These runs may be used to determine the charge
weight.
5.5
Weigh out the compound to the nearest 0.1 g as
previously determined to yield a cull of 3.302 ± 0.254
mm (0.130 ± 0.010 in).
5.6
Raise the ram, add the compound to the pot, and
immediately activate the transfer cycle.
5.7
Remove cull and measure thickness. If the cull is
not within 0.130 ± 0.010 in, discard the run and repeat
the test, adjusting the charge weight as necessary.
5.8
Open mold and measure longe st flash for each
channel to nearest 0.25 mm (0.010 in) using 3×
minimum magnification. Be sure to check both top and
bottom plates of mold before measuring flash.
NOTE: Care must be taken to include the measurement of
transparent and semi-transparent flash which may be present
in the smaller channel. After measurements, diligence is
required to remove all flash, including the transparent and
semi-transparent varieties prior to the next test.
5.9 Repeat Steps 5.6 through 5.8 at least 3 times for
repeatability.
6 Reporting of Results
6.1 Report the material designation and lot number.
6.2 Report the average and standard deviation of the
flash length in each channel.
6.3 Report the temperature and pressure used for the
tests.
NOTE: Common Errors/Problems:
• Inadequate preheat of flash mold and/or transfer
plunger prior to test and between shots.
• Incorrect cull thickness.
• Omission of transparent or semi-transparent flash
in measurement (often present in smallest two
channels).
• Inadequate cleaning of mold between shots.
• Starting from the end of the ruler to make flash
length measurements instead of starting at a known
distance from the end.
• Inadequate mold break-in. Three shots should be
run and disregarded before recording flash
measurements for each material.
• Sprue, channel entry point, and mating mold
surface wear may produce error in measurement
and correlation problem. The impact of wear on
results has not been determined. Extent of
permissible mold wear requires agreement between
testing organizations.
SEMI G45-93 © SEMI 1986, 19933
Figure 1
Flash Test Mold
1. Hand Mold, Polished, Very Well Mated Surfaces, Base Plates 0.75 thk.
2. Mold: Common Runner Feeds Flash Channels of 0.003, 0.0015, 0.0005, and 0.00025 inches by 0.375 wide ±
0.00025.
3. Mold Flash Channels: Surface Finish 8 microinches
4. Mold Flash Channels Depth Tolerance:
a. ± 0.00005" for 0.00025 and 0.0005: Channels
b. ± 0.0002" for 0.0015 and 0.003 Channels
AUXILIARY INFORMATION
Conversions
Inches
Conversions
Millimeters
8.000 203.20
4.500 114.30
2.250 57.15
2.000 50.80
1.125 28.58
1.000 25.40
0.377 9.58
0.375 9.53
0.300 7.62
0.252 6.40
0.250 6.35