ISL8200AMMREP datasheet(21/24 Pages) RENESAS

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ISL8200AMM

FN8287 Rev 2.00

Page 21 of 24

June 3, 2015

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 from 0.3mm to 0.33mm in

diameter with the barrel plated with 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 in the Package Outline

Drawing L23.15x15 on page 24. 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) QFN.

Reflow Parameters

Due to the low mount height of the QFN, "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

QFN. The profile given in Figure 41 is provided as a guideline, to

be customized for varying manufacturing practices and

applications.

FIGURE 41. TYPICAL REFLOW PROFILE

300

100

150

200

250

350

100

150

200

250

300

DURATION (s)

SLOW RAMP (3°C/s MAX)

AND SOAK FROM +100°C

TO +150°C FOR 60s~120s

RAMP RATE

1.5°C FROM +70°C TO +90°C

PEAK TEMPERATURE +215°C~+220°C;

TYPICALLY 60s-70s ABOVE +183°C

KEEP LESS THAN 20s WITH 5°C OF PEAK TEMP.

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