Tape & Reel Surface Mount Package

DATEL's LSM series DC/DC converters are the only higher-current (10A)

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 subsequently reflowed using high-temperature, lead-free solder.

Virtually all SMT DC/DC's today are unprotected "open-frame" devices

assembled 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 melt-

ing 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.

Figure 6. Reflow Solder Profile

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 leads 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 tem-

perature 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.

HEAT SHIELD OUTSIDE TEMPERATURE

Sn96.5/Ag3.5 Melting Point

Sn63/Pb37 Melting Point

250

200

150

100

50

0

50

100

150

200

250

300

350

400

221

183

PCB TEMPERATURE INSIDE THE HEAT SHIELD

Time (Seconds)

LSM-10A D3 Models

10 Amp DC/DC’s in SMT Packages

www.murata-ps.com

MDC_LSM-10A D3.B01 Page 12 of 13