TWR A-Series
20W, Triple Output DC-DC Converters
MDC_TWR20W.E02 Page 7 of 8
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Quality and Reliability
The A-Series are the fi rst DC/DC Converters to emerge from MPS’s new,
company-wide approach to designing and manufacturing the most reliable
power converters available. The fi ve-pronged program draws our Quality
Assurance function into all aspects of new-product design, development,
characterization, qualifi cation and manufacturing.
Design for Reliability
Design for Reliability is woven throughout our multi-phased, new-product-
development process. Design-for-reliability practices are fully documented
and begin early in the new-product development cycle with the following
goals:
1. To work from an approved components/vendors list ensuring the use of
reliable components and the rigorous qualifi cation of new components.
2. To design with safety margins by adhering to a strict set of derating
guidelines and performing theoretical worst-case analyses.
3. To locate potential design weaknesses early in the product-development
cycle by using extensive HALT (Highly Accelerated Life Testing).
4. To prove that early design improvements are effective by employing a
thorough FRACA (Failure Reporting Analysis and Corrective Action) system.
HALT Testing
The goal of the accelerated-stress techniques used by MPS is to force
device maturity, in a short period of time, by exposing devices to excessive
levels of “every stimulus of potential value.” We use HALT (Highly Acceler-
ated Life Testing) repeatedly during the design and early manufacturing
phases to detect potential electrical and mechanical design weaknesses
that could result in possible future fi eld failures.
During HALT, prototype and pre-production DC/DC converters are sub-
jected to progressively higher stress levels induced by thermal cycling,
rate of temperature change, vibration, power cycling, product-specifi c
stresses (such as dc voltage variation) and combined environments. The
stresses are not meant to simulate fi eld environments but to expose any
weaknesses in a product’s electro/mechanical design and/or assem-
bly processes. The goal of HALT is to make products fail so that device
weaknesses can be analyzed and strengthened as appropriate. Applied
stresses are continually stepped up until products eventually fail. After
corrective actions and/or design changes, stresses are stepped up again
and the cycle is repeated until the “fundamental limit of the technology” is
determined.
MPS has invested in a Qualmark OVS-1 HALT tester capable of applying
voltage and temperature extremes as well as 6-axis, linear and rotational,
random vibration. A typical HALT profi le (shown above) consists of thermal
cycling (–55 to +125°C, 30°C/minute) and simultaneous, gradually increas-
ing, random longitudinal and rotational vibration up to 20G’s with load
cycling and applied-voltage extremes added as desired. Many devices in
MPS’s A-Series could not be made to fail prior to reaching either the limits
of the HALT chamber or some previously known physical limit of the device.
We also use the HALT chamber and its ability to rapidly cool devices to
verify their “cold-start” capabilities.
Qualifi cation
For each new product, electrical performance is verifi ed via a comprehen-
sive characterization process and long-term reliability is confi rmed via a
rigorous qualifi cation procedure. The qual procedure includes such strenu-
ous tests as thermal shock and 500 hour life. Qual testing is summarized
below.
In-Line Process Controls and Screening
A combination of statistical sampling and 100% inspection techniques
keeps our assembly line under constant control. Parameters such as
solder-paste thickness, component placement, cleanliness, etc. are statisti-
cally sampled, charted and fi ne tuned as necessary. Visual inspections are
performed by trained operators after pick-and-place, soldering and cleaning
operations. Units are 100% electrically tested prior to potting. All devices
are temperature cycled, burned-in, hi-pot tested and fi nal-electrical tested
prior to external visual examination, packing and shipping.
Rapid Response to Problems
MPS employs an outstanding corrective-action system to immediately
address any detected shortcomings in either products or processes. When-
ever our assembly, quality or engineering personnel spot a product/process
problem, or if a product is returned with a potential defect, we immediately
perform a detailed failure analysis and, if necessary, undertake corrective
actions. Over time, this system has helped refi ne our assembly operation to
yield one of the lowest product defect rates in the industry.
Typical HALT Profi le
Qualifi cation Test Method/Comments
HALT MPS in-house procedure
High Temperature Storage Max. rated temp., 1,000 hours
Thermal Shock 10 cycles, –55 to +125°C
Temperature/Humidity +85°C, 85% humidity, 48 hours
Lead Integrity MPS in-house procedure
Life Test +70°C, 500 hours*
Marking Permanency MPS in-house procedure
End Point Electrical Tests Per product specifi cation
Qualifi cation Testing
* Interim electrical test at 200 hours.
10 20 30 40 50 60 70 80 90
40
20
0
Random Vibration (G's)
Temperature (°C)
Test Ti me (minutes)
100
80
60
40
20
0
–20
–40
