ISL8272M Datasheet, PDF (24/56 Pages) Intersil Corporation – 50A Digital DC/DC PMBus Power Module

ISL8272M
PCB Layout Pattern Design
The bottom of ISL8272M is a lead-frame footprint, which is
attached to the PCB by surface mounting process. The PCB
layout pattern is shown on page 56. The PCB layout pattern is
essentially 1:1 with the HDA exposed pad and I/O termination
dimensions. The thermal lands on the PCB layout should match
1:1 with the package exposed die pads.
Thermal Vias
A grid of 1.0mm to 1.2mm pitch thermal vias, which drops down
and connects to buried copper plane(s), should be placed under the
thermal land. The vias should be about 0.3mm to 0.33mm in
diameter with the barrel plated to about 1.0 ounce copper.
Although adding more vias (by decreasing via pitch) will improve
the thermal performance, diminishing returns will be seen as more
and more vias are added. Simply use as many vias as practical for
the thermal land size and your board design rules allow.
Stencil Pattern Design
Reflowed solder joints on the perimeter I/O lands should have
about a 50µm to 75µm (2mil to 3mil) standoff height. The solder
paste stencil design is the first step in developing optimized,
reliable solder joins. Stencil aperture size to land size ratio should
typically be 1:1. The aperture width may be reduced slightly to help
prevent solder bridging between adjacent I/O lands. To reduce
solder paste volume on the larger thermal lands, it is
recommended that an array of smaller apertures be used instead
of one large aperture. It is recommended that the stencil printing
area cover 50% to 80% of the PCB layout pattern. A typical solder
stencil pattern is shown on page 55. The gap width between pad to
pad is 0.6mm. The user should consider the symmetry of the
whole stencil pattern when designing its pads. A laser cut,
stainless steel stencil with electropolished trapezoidal walls is
recommended. Electropolishing “smooths” the aperture walls
resulting in reduced surface friction and better paste release which
reduces voids. Using a Trapezoidal Section Aperture (TSA) also
promotes paste release and forms a “brick like” paste deposit that
assists in firm component placement. A 0.1mm to 0.15mm stencil
thickness is recommended for this large pitch (1.3mm) HDA.
Reflow Parameters
Due to the low mount height of the HDA, “No Clean” Type 3 solder
paste per ANSI/J-STD-005 is recommended. Nitrogen purge is
also recommended during reflow. A system board reflow profile
depends on the thermal mass of the entire populated board, so it
is not practical to define a specific soldering profile just for the
HDA. The profile given in Figure 27 is provided as a guideline, to
be customized for varying manufacturing practices and
applications.
300 _{PEAK TEMPERATURE ~+245°C;}
TYPICALLY 60s-150s ABOVE +217°C
250 ^{KEEP LESS THAN 30s WITHIN 5°C OF PEAK TEMP.}
200 _{SLOW RAMP (3°C/s MAX)}
AND SOAK FROM +150°C
150 ^{TO +200°C FOR 60s~180s}
100
RAMP RATE 1.5°C FROM +70°C TO +90°C
50
0
0
100
150
200
250
300
350
DURATION (s)
FIGURE 27. TYPICAL REFLOW PROFILE
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FN8670.3
March 16, 2016