AD9854SLASHPCB datasheet(34/44 Pages) AD

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AD9854

–34–

REV. 0

THERMALLY ENHANCED PACKAGE MOUNTING

GUIDELINES

The following are general recommendations for mounting the

thermally enhanced exposed heat sink package (AD9854ASQ)

to printed circuit boards. The exceptional thermal characteristics of

this package depend entirely upon proper mechanical attachment.

Figure 58 depicts the package from the bottom and shows the

dimensions of the exposed heat sink. A solid conduit of solder

needs to be established between this pad and the surface of

the PCB.

UNT

14mm

10mm

Figure 58.

Figure 59 depicts a general PCB land pattern for such an exposed

heat sink device. Note that this pattern is for a 64-lead device not

an 80-lead, but the relative shapes and dimensions still apply.

In this land pattern, a solid copper plane exists inside of the

individual lands for device leads. Note also that the solder mask

opening is conservatively dimensioned to avoid any assembly

problems.

SOLDER MASK

OPENING

THERMAL LAND

Figure 59.

The thermal land itself must be able to distribute heat to an even

larger copper plane such as an internal ground plane. Vias must be

uniformly provided over the entire thermal pad to connect to this

internal plane. A proposed via pattern is shown in Figure 60. Via

holes should be small (12 mils, 0.3 mm) such that they can be

plated and plugged. These will provide the mechanical conduit

for heat transfer.

Figure 60.

Finally, a proposed stencil design is depicted for screen solder

placement. Note that if vias are not plugged, wicking will occur

which will displace solder away from the exposed heat sink and

the necessary mechanical bond will not be established.

Figure 61.

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