www.sensirion.com / D1

Version 4

– December 2022

20/24

Parameter

Symbol

Min

Nom. Max Units

Comments

Package height

A

0.8

0.9

1

mm

Leadframe height

A3

-

0.2

-

mm

Pad width

b

0.2

0.25

0.3

mm

Package width

D

2.4

2.5

2.6

mm

Center pad length

D2

1

1.1

1.2

mm

Package length

E

2.4

2.5

2.6

mm

Center pad width

E2

1.7

1.8

1.9

mm

Pad pitch

e

-

0.5

-

mm

Pad length

L

0.25

0.35

0.45

mm

Center pad marking

T1xT2

-

0.3x45°

-

mm

indicates the position of pin 1

Table 21. Package outline.

5.3 Land Pattern

The land pattern (Figure 6) is understood to be the open metal areas on the PCB, onto which the

DFN pads are soldered. The solder mask is understood to be the insulating layer on top of the PCB

covering the copper traces. It is recommended to design the solder pads as a Non-Solder Mask

Defined (NSMD) type. For NSMD pads, the solder mask opening should provide a 60

μm to 75 μm

design clearance between any copper pad and solder mask. As the pad pitch is only 0.5 mm we

recommend to have one solder mask opening for all four I/O pads on one side. For solder paste

printing it is recommended to use a laser-cut, stainless steel stencil with electro-polished

trapezoidal walls and with 0.1 or 0.125 mm stencil thickness. The length of the stencil apertures for

the I/O pads should be the same as the PCB pads. However, the position of the stencil apertures

should have an offset of 0.1 mm away from the center of the package. The die pad aperture should

cover about 70%

– 90% of the die pad area –thus it should have a size of about 0.9 mm x 1.6 mm.

For information on the soldering process and further recommendation on the assembly process

please consult the Handling Instructions [3], which can be found on the Sensirion webpage.

Figure 6. Recommended metal land pattern (left) and stencil apertures (right) for the STS32/33-DIS. The

dashed lines represent the outer dimension of the DFN package. The PCB pads (left) and stencil apertures

(right) are indicated through the shaded areas.

Recommended Land Pattern

Recommended Stencil Aperture

0.55

1

2.35

0.2

0.9

0.55

2.55

0.3