Question about the size of via

[circuit]

size of via ?

Hello, Is it better to have a via of bigger diameter for connecting the power/ground signals...i know that a bigger dia means a bigger capacitance, i use a 10 mil drill dia for the high speed signals...so for power signals, i should use something like 25 mils ?

 

[newbie101]

Re: size of via ?

hmm.... i wanted to ask the same question also

1) if inner radius of via is 'r' then effective trace width of via would be 2×pi×r , so i guess bigger via would mean wider trace connection.

2) since we have wider trace.. capacitance would also be larger.. dont know if this is good or bad

3) larger diameter would mean smaller partial mutual inductance inside via... so smaller impedance of via... maybe this is good

4) also if we are trying to reduce effective inductance by placing two vias ( one power and one ground ) close together for decoupling caps.... then larger diameter makes this more difficult.... so it wouldnt help in this case.

please comment on it..... thanks

regards,
newbie

 

[binu G]

size of via ?

hi,
i have seen in the mobile boards the via's which are very small such that with the visual eye its difficult to identify.
Do any one have more info regarding such via.
what is the drill size, and the details of the fabricaton process.

Binu G

 

[amjad]

Re: size of via ?

Yes, you can have 25 mils drill for power and gnd nets, but if you know the voltage and current carrying capacity , then you can decide upon using the drill sizes which will be related as atleast 60% percentage of all the thermal relief must be compatible to the drill dia

 

[AMCC]

Re: size of via ?

Hi,

Size o via is important.
On trace signal they should be as small as possible to minimize inductance (that may cause signal slowing down or small glitches). (Answering Binu G: The vias are probably "microvias" typically from outer layer to first inner layer, typical size may be of a few hundred microns)

On power supply the only requirment for vias is: PUT A LOT (and if you can place a few more ... then place it ) (Note: Be sure that your foundry doesn't get paid on the number of vias...)
Capacitance is not a concern on vias since if you add a 100 nF decoupling capacitor you are probably adding more capacitance that you power vias all together. But impedance (specially inductance and resistance) should be as lower as possible...
A final note: Vias that connect power sources to distribution planes should be bigger (typiccaly 50 dependeng on current)... and as many as possible to increase power dissipation.

I hope this helps.

AMCC

 

[binu G]

size of via ?

can any one suggest the via pad size and drill for a BGA with 0.80 mml pitch and 0.65 mm pitch?

also the internal pad size for the same.

thanks

binu g

 

[fyjin]

size of via ?

Who can give formula about pitch and pad and via size.

 

[touringmike]

Re: size of via ?

can any one suggest the via pad size and drill for a BGA with 0.80 mml pitch and 0.65 mm pitch?

also the internal pad size for the same.

thanks

binu g

Depends upon the board house you use. I've used .016pad/.008drill to avoid extra charges that laser drills require. The internal pad is .020. If you have a large count FBGA that requires laser drilling, then .013pad/.005drill is what I've seen in both fan-outs from the pad, and a .005 drill in the pad of the BGA down one layer to a buried via.

 

[binu G]

size of via ?

what about the internal pad size for the laser drill?

 

[touringmike]

Re: size of via ?

The buried via pad size for the .005 hole is normally the same through-out the design, .013. That is what I use without any complaints from the fabricator.

I also use a .020 pad/.010 drill for all layers where space permits, and .016 pad/.008 drill in tight areas. Increasing the internal pad size is a recommendation that isn't necessarily required. Again, this depends upon the fabricator you are using.

 

[sigint]

Re: size of via ?

The formula for the equivalent trace width is either 2r x 3.141 or the diameter x 3.141 always remember even if you have 2 Oz. Cu on the surface the plating in the hole will only be 1 Oz. or less - fewer large vias are fine or many small vias your choice since you are worried about having a low inductance path the more via's the better.

SiGiNT

 

[binu G]

size of via ?

what should be the value of anular ring for a via ?

binu G

 

[amjad]

Re: size of via ?

10mil Annular ring is standard for a via. Minimum can be 5mil or even less depending upon your manufacturing capability and the design. Generally, till 7.5mil annular ring is advisable, if you don't prefer 10mil.