LSM16A-W3 Datasheet, PDF (11/12 Pages) Murata Manufacturing Co., Ltd. – Non-Isolated, Wide Input SMT DC/DC Converters

LSM-16A W3 Models
Non-Isolated, Wide Input SMT DC/DC Converters
Tape & Reel Surface Mount Package
DATEL’s LSM series DC/DC converters are the only higher-current (16A) SMT
DC/DC’s 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 subse-
quently reflowed using high-temperature, lead-free solder.
Virtually all SMT DC/DC’s today are unprotected “open-frame” devices assem-
bled by their vendors with high-temperature solder (usually Sn96.5/Ag3.5
with a melting point +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 limita-
tions, 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 compro-
mise the reliability of their solder joints. Virtually all these devices demand you
“cool down” the Sn63 profile you are likely using today.
DATEL 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, straightforward approach that works. We assemble our LSM SMT
DC/DC’s 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 (100μ1m) of the unit’s copper leads. These units are
gold-plated with a nickel underplate. See Mechanical Data for additional
information.
The disposable heat shield (patent pending), which has a cutaway exposing
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
exceeding 2 minutes above 221°C (the melting point of Sn96.5/Ag3.5) are
easily achieved.
250
221
200
183
150
100
50
0
Sn96.5/Ag3.5 Melting Point
Sn63/Pb37 Melting Point
HEAT SHIELD OUTSIDE TEMPERATURE
PCB TEMPERATURE INSIDE THE HEAT SHIELD
50
100
150
200
250
300
Time (Seconds)
Figure 6. Reflow Solder Profile
350
400
www.murata-ps.com
Technical enquiries email: [e-mail], tel: [phone]
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