Hardware (designing PCB schematics and layout)

AN4450

10/26

DocID025978 Rev 1

Figure 6. Recommended land and solder mask design for *LGA packages



A = Clearance from PCB land edge to solder mask opening

solder mask is opened externally to device area



B = PCB land length = *LGA solder pad length + 0.1 mm



C = land width = *LGA solder pad width + 0.1 mm



D = Solder mask opening length = PCB land length + 0.3 mm: design 0.05 mm inside

and 0.25 mm outside



E = Solder mask opening width = PCB land width + 0.1 mm

2.2.2

Stencil design and solder paste application

The soldering paste thickness and pattern are important for a proper pressure sensor

mounting process.



Stainless steel stencils are recommended



Stencil thickness of 90 - 150 µm (3.5 - 6 mils) is recommended for screen printing



The final soldering paste thickness should allow proper cleaning of flux residues and

clearance between sensor package and PCB



Stencil aperture should have a rectangular shape with dimensions up to 25 µm (1 mil)

smaller than PCB land



The openings of the stencil for the signal pads should be between 70 - 80% of the PCB

pad area



Optionally, for better solder paste release, the aperture walls should be trapezoidal and

the corners rounded



The fine IC leads pitch requires accurate alignment of the stencil to the PCB. The

stencil and printed circuit assembly should be aligned to within 25 µm (1 mil) prior to

application of the solder paste

2.2.3

Process consideration

In using non self-cleaning solder paste, proper board washing after soldering must be

carried out to remove any possible sources of leakage between pads due to flux residues.

However, take care not to perform the cleaning process on top of the pressure sensor.