ISL8270MEVAL1Z datasheet(21/56 Pages) RENESAS

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ISL8270M

FN8635 Rev.4.00

Page 21 of 56

Aug 17, 2017

Thermal Considerations

Experimental power loss curves, along with θJA from thermal

modeling analysis, can be used to evaluate the thermal

consideration for the module. The derating curves are derived

from the maximum power allowed while maintaining the

temperature below the maximum junction temperature of

+125°C. In actual applications, other heat sources and design

margins should be considered.

Package Description

The structure of the ISL8270M belongs to the High Density Array

(HDA) no-lead package. This kind of package has advantages,

such as good thermal and electrical conductivity, low weight, and

small size. The HDA package is applicable for surface mounting

technology and is being more readily used in the industry. The

ISL8270M contains several types of devices, including resistors,

capacitors, inductors, and control ICs. The ISL8270M is a copper

lead-frame based package with exposed copper thermal pads,

which have good electrical and thermal conductivity. The copper

lead frame and multi-component assembly is over-molded with

polymer mold compound to protect the devices.

The package outline, a typical PCB land pattern design, and a

typical stencil opening edge position are shown on pages 53 and

54 respectively. The module has a small size of

17mmx19mmx3.55mm. Figure 31 shows the typical reflow

profile parameters. These guidelines are general design rules.

Users can modify parameters according to their application.

PCB Layout Pattern Design

The bottom of the ISL8270M is a lead-frame footprint, which is

attached to the PCB by the surface mounting process. The PCB

land pattern is shown on page 53. 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 (2 mil to 3 mil) 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 can 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 54. 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, thus

it is not practical to define a specific soldering profile just for the

HDA. The profile given in Figure 31 is provided as a guideline, to

be customized for varying manufacturing practices and

applications.

FIGURE 31. TYPICAL REFLOW PROFILE

0300

100

150

200

250

350

100

150

200

250

300

DURATION (s)

SLOW RAMP (3°C/s MAX)

AND SOAK FROM +150°C

TO +200°C FOR 60s~180s

RAMP RATE

1.5°C FROM +70°C TO +90°C

PEAK TEMPERATURE ~+245°C;

TYPICALLY 60s-150s ABOVE +217°C

KEEP LESS THAN 30s WITHIN 5°C OF PEAK TEMP

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