What is the purpose of doing a fanout on an SMT chip?

[ZackG]

What is the purpose of the fanout? By this I mean a step by which the autorouter lays small circular pads next to connected pins on an SMT chip.

 

[cyberrat]

Although not too sure as I have never done this, but I would assume that it's so that there is a std way of the tracks exiting away from the IC, that is good for thermal conductivity, AOI, good t/t spacing etc.

Then from the fan'ed out pad you can then track off in as many directions as you wish.

Perhaps?

 

[Ajish Babu S]

When use S.M.D. pads in PCB , these pads can be accessed only on one layer. To access an SMD pad from another layer of the PCB requires a via called escape vias and escape wires are used to connect the SMD pad to the via created. Hence the pattern generated with the escape wires and vias refers to the fanout pattern.The process of creating dispersion vias for SMD devices on your printed circuit board is called fanout.

 

[cyberrat]

Tha's what I meant, good description Ajish...

 

[Bengt]

The meaning of fan-out is usually the minimum distance from the pad to the via. The reason to have a fan-out and not put the via in direct connection to the pad is that you want to have solder mask isolation between the pad and the via to avoid the via steeling solder from the pad during the soldering process.

 

[ZackG]

Thank you guys! That was very helpful! I get it now!

 

[jayasuryan]

Hello.....

In the case of surface mount devices attached to double-sided or multilayer boards, each component pad is usually connected by a short length of track to a via which forms a link to other conducting layers, and this via is known as a fan-out via. The term fan-out via is generally also taken to include any vias that fall inside the device's footprint (under the body of the device). Some designers attempt to differentiate these vias from those that fall outside the device's footprint by referring to them as fan-in vias, but this is not an industry-standard term.