LSM16A-D12 Datasheet, PDF (11/12 Pages) Murata Manufacturing Co., Ltd. – Non-Isolated, 13-80W SMT DC/DC Converters

LSM-16A D12 Models
Non-Isolated, 13-80W SMT DC/DC Converters
Tape & Reel Surface Mount Package
Murata Power Solutions’ LSM series DC/DC converters are the only higher-
current (16A) SMT DC/DCs that can be automatically “pick-and-placed” using
standard vacuum-pickup equipment (nozzle size and style, vacuum pressure
and placement speed may need to be optimized for automated pick and place)
and subsequently reflowed using high-temperature, lead-free solder.
Virtually all SMT DC/DCs today are unprotected “open-frame” devices
assembled by their vendors with high-temperature solder (usually Sn96.5/
Ag3.5 with a melting point of +221°C) so that you may attach them to your
board using low-temperature solder (usually Sn63/Pb37 with a melting point
of +183°C). Conceptually straightforward, this “stepped” solder approach has
its limitations, and it is clearly out of step with an industry trending toward
the broad use of lead-free solders. Are you to experiment and develop reflow
profiles from other vendors that ensure the components on those DC/DC never
exceed 215–216°C? If those components get too hot, “double-reflow” could
compromise the reliability of their solder joints. Virtually all these devices
demand you “cool down” the Sn63 profile you are likely using today.
MPS is not exempted from the Laws of Physics, and we do not have magic
solders no one else has. Nevertheless, we have a simple and practical, straight-
forward approach that works. We assemble our LSM SMT DC/DCs using a
high-temperature (+216°C), lead-free alloy (Sn96.2%, Ag2.5%, Cu0.8%,
Sb0.5%). The LSM design ensures co-planarity to within 0.004 inches (100μm)
of the unit’s copper leads. These leads are gold-plated with a nickel underplate.
See Mechanical Data for additional information.
The disposable heat shield (patent pending), which has a cutaway expos-
ing the package leads, provides thermal insulation to internal components
during reflow and its smooth surface ideally doubles as the vacuum pick-up
location also. The insulation properties of the heat shield are so effective that
temperature differentials as high as 50°C develop inside-to-outside the shield.
Oven temperature profiles with peaks of 250–260°C and dwell times exceed-
ing 2 minutes above 221°C (the melting point of Sn96.5/Ag3.5) are easily
achieved.
250
Sn96.5/Ag3.5 Melting Point
221
200
Sn63/Pb37 Melting Point
183
HEAT SHIELD OUTSIDE TEMPERATURE
150
PCB TEMPERATURE INSIDE THE HEAT SHIELD
100
50
0
50
100
150
200
250
300
350
400
Time (Seconds)
Figure 6. Reflow Solder Profile
www.murata-ps.com
Technical enquiries email: [e-mail], tel: [phone]
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