PNI SENtral - Manual (Page 37)

PNI Sensor Corporation Doc #1018049 R03
SENtral Technical Data Sheet Page 36
8 Assembly Guidelines
SENtral is provided in a lead-free wafer-level chip-scale package (WL-CSP). General design
guidelines can be found in Amkor’s “Application Note for Surface Mount Assembly of Amkor’s
Eutectice and Lead-Free CSP
nl 
Wafer Level Chip Scale Packages”, which is available from
Amkor’s website. Specific assembly guidelines are discussed below.
Comments specific to SENtral include:

Microvia technology is NOT required if GPIO[3] and GPIO[5] are not used and the
slave address pin, SA0, is set LOW. In this case the slave address pin, C3, should be
connected to C2 (unused), and C2 should be connected to D2, which is GND. Pins
B2, GPIO[5], and B3, GPIO[3], should be left unconnected.

If either GPIO[3] and GPIO[5] are to be used or the slave address pin, SA0, is to be
set HI, then microvia technology is required. Due to SENtral’s ball-grid-array 0.4
mm pitch and 0.26 mm ball diameter, connections to these inner pins should be made
with a via-in-pad design using microvias.
General CSP assembly guidelines for SENtral include:

A non-solder mask defined (NSMD) land pattern is recommended.

Solder mask registration is critical and the correct solder mask opening dimension
should be 50um either side of the copper pad.

The actual size of the copper pad should be between 80% and 100% of the diameter
of the solder ball.

The copper layer thickness should 30 um or less.

The copper pads should be finished with Organic Solderability Preservative (OSP)
coating, such as ENTEK-PLUS Cu 106A.

Standard epoxy glass PCB substrates are compatible. High temperature FR4 is
preferred over standard FR4 for improved package reliability.