DC DC Converters Mechanical

Application Note - Interpoint
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting,
Vibration and Shock
HANDLING PRECAUTIONS
Interpoint metal packaged power converters have compression
glass seals around the pins and, as such, should be handled
carefully to protect the integrity of the seal. Refer to Figure 1.
For example, dropping a part on a pin from only a short distance
will almost certainly result in cracking of the glass bead and
consequent loss of hermeticity. A significant drop with contact on
almost any part of the metal case may result in permanent seal
or other type of damage. Anything that bends or twists the pins
may fracture the glass, possibly cracking the substrate.
Never cut an unsupported pin with a pair of side cutters or by
other means. The resulting shock will crack the glass sealing
bead. To cut pins before mounting the part on a PC card or other
structure, the pins must be supported. A gauge block or other
tool which slips over the pins, and incorporates features similar to
those shown in Figure 1, should be used for support. Once this
is done, the pins can be cut or sheared with a sharp blade. If the
part is mounted and soldered on a PC card before cutting the
pins, the solder joints will provide the support for safe cutting.
MOUNTING ON PC CARD OR METAL PLATE
Figure 2 shows a typical metal case configuration used for MTO
and some MTR type power converters. There are nine func-
tion pins which exit the mounting base through glass sealing
and insulating beads, and one case ground pin which is brazed
into the mounting base. The mounting base is also the thermal
surface from which internally generated heat is intended to be
removed by conduction.
The case pin is intended for connection to a ground plane which
connects to other components such as the power line filter case
pin or case bypass capacitors used for Common Mode noise
suppression. If the power converter is mounted on a PC Card
with some clearance from the board for cleaning or inspection,
then the internally generated heat will be removed mainly by
convection not by conduction. For the case example used, the
thermal resistance from case to still air will be about 18°C/watt
of internally generated heat, and will be dependent on orienta-
tion. For operation at 10 watts output power and 80% efficiency,
the internal power loss will be 2.5 watts, and the case will rise
on the order of 45°C above the ambient air. This may be an
inadequate thermal solution, with the removal of some heat by
conduction necessary. Mounting on a short thermal ladder using
a ceramic or other thermally conductive spacer will help lower the
case temperature while still allowing inspection of solder joints.
GAUGE BLOCK OF HARDENED STEEL TO STRAIGHTEN AND HOLD PINS
AND SEAT ON UNIT BASE. PINS CAN BE CUT TO PROPER LENGTH
OR BY OTHER MEANS WHEN GAUGE BLOCK IS SEATED ON UNIT BASE.
THROUGH HOLES WITH FLARE TO STRAIGHTEN
PINS AND HOLD PINS IN PLACE.
PIN LENGTH
GAUGE BLOCK: HARDENED STEEL
UNIT WITH PINS TO BE CUT OFF
GLASS SEALING BEADS
Figure 1: Cutting Pins sealed With ComPression glass
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting, Vibration and Shock
ApplicAtion note
Although the concepts stated are universal, this application note was written specifically for Interpoint products.
Crane Aerospace & Electronics
Crane Electronics Group (Interpoint Brand)
PO Box 97005 • Redmond WA 98073-9705
425.882.3100 • [email protected]
www.interpoint.com
Page 1 of 5
Rev D - 20090310
Mounting on the core of an aluminum cored PC Card or other
metal structure with a thermal pad interface to fill air voids would
be a better thermal solution. Painting the case a dull black will
take advantage of radiation where convection is ineffective. See
our “Thermal Management” application note for more detailed
information.
Where vibration and/or shock of significance is a system require-
ment, some additional precautions might be considered. Use a
flange mounted case, and if on a PC or aluminum cored board,
mount it as close as possible to the support rails rather than
toward the center of the board. This should improve the thermal
situation also. Secure to the board with fasteners at the flanges
or by other means. Devices which are secured by the pins only,
and in particular those with the smaller 0.018 inch diameter pins,
can be in danger of having the pins sheared off during vibration.
The problem can be reduced by securing the device with epoxy
or other means, or by using flying leads for stress relief rather
than soldering directly to the PC card. Examples of vibration and
shock conditions with comments on how they are tested follow.
RANDOM VIBRATION
Interpoint power converters are rugged devices which will with-
stand high levels of vibration and shock, provided the structure
to which they are mounted is free of resonances having signifi-
cant Q’s. A high Q indicates a lack of damping, and Q’s of 1 or
less are desirable, but often hard to realize. Random Vibration is
characteristic of real world conditions and is a situation where all
frequencies within the vibration bandwidth have an equal proba-
bility of being present at any one time, hence the term “Random”
to describe the vibration spectrum.
The Random test spectrum is generated from a clipped white
noise generator which is followed by a group of band shaping
filters and conditioning circuits feeding into a power amplifier
which provides the electrical input to the shaker pot armature. A
typical vibration spectrum is shown in Figure 3. Here the vertical
axis, power spectral density, has units of G
2
/Hz. The horizontal
axis is Log Frequency, and has units of Hz. The RMS G level of
the Random Spectrum over a given bandwidth is found from the
square root of the area under the vibration curve over the given
bandwidth. For example, the flat spectrum of Figure 4 having a
PSD of 0.5 G
2
/Hz over the bandwidth of 20 to 2000 Hz, has an
RMS level of 31.5 G
RMS
. This vibration spectrum and level are
within what is possible with Interpoint power converters provided
the mounting means is free of significant resonances.
CERAMIC, .02-.03 INCHES
THICK, EPOXIED IN PLACE.
SOME MATERIALS ARE:
• ALUMINA: Al2O3
• ALUMINUM NITRIDE: AlN3
THERMAL PAD, 0.01 INCHES THICK
FUNCTION PINS -
ALLOY 52
MOUNTING BASE AND
THERMAL SURFACE
CASE PIN -
ALLOY 52
CASE AND COVER:
COLD ROLLED STEEL
BETTER THERMAL SITUATION: MOUNT TO METAL CORED OR WEBB
TYPE P.C. CARD TO REDUCE THERMAL RESISTANCE TO HEAT
CONDUCTION, FLYING LEADS OR FLEX CIRCUIT LEADS CAN BE USED
FOR ELECTRICAL CONNECTIONS.
MOUNTING ON P.C. CARD OVER COPPER TRACES: USE CERAMIC,
OR OTHER INSULATING MATERIAL, TO PROTECT TRACES AND
RAISE BASE ABOVE P.C. CARD. NOT A GOOD THERMAL SOLUTION.
Figure 2: mounting PoWer Converter to PC Card
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting, Vibration and Shock
ApplicAtion note
www.interpoint.com Page 2 of 5
Rev D - 20090310
Interpoint does not screen for vibration except on a special order
basis. We do however run qualification tests on new parts and,
when vibration is included, we make sure that a resonance free
mounting means is used. A resonance free means is achieved
with an aluminum block, securely mounted to the shaker head,
with cavities into which the power converters are inserted and
then potted with wax. The vibration test may be run with or
without power applied to the test samples.
Interpoint does apply constant acceleration to screened parts,
500 G or 5000 G, depending on the screening level. This is a
static test done by centrifuging, and not in any way related to
vibration.
SINUSOIDAL VIBRATION
Sinusoidal vibration involves one discrete frequency at a time,
with the frequency swept back and forth over the defined band-
width at a predetermined rate. The test vibration is generated
by a sine wave sweep generator which drives a power ampli-
fier supplying the electrical signal for the shaker pot armature.
Testing for susceptibility to sinusoidal vibration usually involves
dwelling at frequencies where structural resonances are discov-
ered. This is a more severe test than Random Vibration where
the RMS levels are the same. Figure 5 is taken from MIL-STD-
202 and shows examples of different conditions of sinusoidal
vibration. The graph has P-P, Double Amplitude, displacement
on the vertical axis plotted against Log Frequency on the hori-
zontal axis. The sloping straight lines are of constant accelera-
tion (conditions A through H) and all revert to a horizontal line
representing a constant P-P displacement of 0.06 inches at
lower frequencies of 60 to 200 Hz, depending on condition. The
constant displacement vibration mode at low frequencies is due
to the shaker pot armature being displacement limited.
SHOCK
Examples of shock conditions which Interpoint power converters
are capable of surviving are shown in Figure 6. Survival assumes
a resonance free mounting means. For shock levels higher than
those shown in the example, repeated applications may cause
cracking in magnetic components, followed by power train elec-
trical failures. Other mechanical type failures may also occur.
dB = 10 log
G
2
/ Hz
= 20 log
G / Hz
THE RMS VALUE OF ACCELERATION WITHIN A
FREQUENCY BAND BETWEEN f
1
AND f
2
IS:
G
rms
=



(G
2
/ Hz) df
WHERE G
2
/ Hz IS A GIVEN REFERENCE VALUE OF
POWER-SPECTRAL DENSITY, USUALLY THE MAXIMUM
SPECIFIED VALUE.
G
2
/ Hz G
r
/

Hz
CHARACTERISTICS
POWER
SPECTRAL
DENSITY
0.02
0.04
0.06
0.10
0.20
0.30
0.40
0.60
1.00
1.50
TEST
CONDITION
LETTER
A
B
C
D
E
F
G
H
J
K
OVERALL
rms G
5.2
7.3
9.0
11.6
16.4
20.0
23.1
28.4
36.6
44.8
P
S
D

–

(
G

2
/

H
z
)
VIBRATION FREQUENCY IN Hz
FROM MIL-STD-202
r
r
f
1
f
2
1
/
2
0.10
0.15
0.20
0.25
0.30
0.40
0.50
0.70
1.00
1.50
2.00
20 30 50 100 1000 2000
UPPER TOLERANCE LIMIT (+1.5dB)
SPECIFIED CURVE
6dB/OCTAVE
2
4
d
B
/
O
C
T
A
V
E
6
d
B
/
O
C
T
A
V
E
LOWER TOLERANCE
LIMIT (–1.5dB)
2
4
d
B
/
O
C
T
A
V
E
Figure 3: tyPiCal random vibration ProFile
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting, Vibration and Shock
ApplicAtion note
www.interpoint.com Page 3 of 5
Rev D - 20090310
1.0
0.5
0.1
0.05
A
C
C
E
L
E
R
A
T
I
O
N

P
O
W
E
R

S
P
E
C
T
R
A
L

D
E
N
S
I
T
Y

(
g
2

/
H
z
)
2000
LOG FREQUENCY (Hz)
200 20
G
RMS
=
(0.5) (2000 – 20) = 31.5G
RMS

Figure 4: random vibration - Flat sPeCtrum
DISPLACEMENT =
DA
SIN t
=
2
and f =
1
ACCELERATION =
DA
2
SIN t
G
PEAK
= 0.051 f
2
DA
f = HERTZ
DA = INCHES PEAK-TO-PEAK
CONDITIONS A,B,C,D,
E,F,G,H.
CONDITION H 80G
CONDITION E
CONDITION D AND F
CONDITION G
CONDITION A
CONDITION D
CONDITIONS AAND C
CONDITION B
20G 10G
15G
50G
30G
NOTE: Test condition A ends at 500 Hz.
Test conditions B, C, D, E, G and H end at 2,000 Hz.
Test condition F ends at 3,000 Hz.
10,000 2,000 500 100
79 161.3
10 5
.00001
.00005
.0001
.001
.01
.06
.1
V
I
B
R
A
T
I
O
N

A
M
P
L
I
T
U
D
E

(
D
O
U
B
L
E

A
M
P
L
I
T
U
D
E

–

I
N
C
H
)
VIBRATION FREQUENCY (Hz)
DA
A
T
2
T T
2
Figure 5: sine vibration
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting, Vibration and Shock
ApplicAtion note
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Rev D - 20090310
1.15A
A
.85A
SINE WAVE TRANSLATED
UP BY AN AMOUNT .15A
SINE WAVE (IDEAL).
SINE WAVE TRANSLATED
DOWN BY AN AMOUNT .15A
D .1D
–.2A
0
.2A
.05A
0
–.05A
1/2 SINE
1.15P
P
.85P
IDEAL SAWTOOTH PULSE
.07D
.07D
+.2P
0
–.2P
D .4D
+.15P
–.15P
+.05P
0
–.05P
SAWTOOTH
TABLE 213-1. TEST CONDITION VALUES
TEST
CONDITION
A
B
C
D
E
F
G
H
I
J
K
PEAK VALUES
(g’s)
NORMAL
DURATION (D) (ms)
11
6
6
1
0
0
11
6
6
11
11
WAVEFORM
HALF-SINE
HALF-SINE
HALF-SINE
HALF-SINE
HALF-SINE
HALF-SINE
SAWTOOTH
SAWTOOTH
SAWTOOTH
HALF-SINE
SAWTOOTH
.5
.5
50
75
100
500
1,000
1,500
50
75
100
30
30
.4D
Figure 6: tyPiCal shoCk Conditions
Crane Aerospace & Electronics Power Solutions
Mechanical: Mounting, Vibration and Shock
ApplicAtion note
Mechanical Rev D - 20090310. All information is believed to be accurate, but no responsibility is assumed for errors or omissions.
Interpoint reserves the right to make changes in products or specifications without notice. Copyright © 1999 - 2009 Interpoint
Corporation. All rights reserved. www.interpoint.com
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