13.3.2. PCB design and SMD manufacturing process considerations

Since the epc901 chip comes in a very small 32 pin chip scale package, the PCB layout should be made with special care. Since the

silicon chip is small and light weight compared to the solder balls, it is highly recommended that all tracks to the chip should come straight

from the side. A consequent symmetrical design is therefore highly recommended to achieve high production yield.

The pads and the tracks should also have exactly the same width and shall be covered by a solder resist mask in order to avoid drain of

the solder tin alloy to the track.

8.000

ø0.4

solder resist mask

solder resist mask opening

track

(straight only for 0.25mm!)

landing pad

ø0.3

max. 0.15

chip perimeter

all measures in mm

Figure 17: Recommended PCB layout

Underfill of the components reduces stress to the solder pads caused by e.g. temperature cycling or mechanical bending.The thermal and

mechanical fatigue will be reduced and the longterm reliability will be increased. Underfill and underfill selection is application specific. It

shall follow JEDEC-STD JEP150: Stress-Test-Driven Qualification of and Failure Mechanisms Associated with Assembled Solid State

Surface- Mount Components.

from the ESPROS website at www.espros.com/application-notes. Obeying the recommendations in the applications AN04, a high manu-

facturing yield can be achieved.

© 2016 ESPROS Photonics Corporation

Characteristics subject to change without notice

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