[SI-LIST] Re: Advantages & Disadvantages of Flooding Vias??

Hi Manatosh,

If you design a cockpit control board, it does not sound like a home 
hobby project, so you should
have ready access to the people who are going to fabricate and assemble 
the board.  The board
fabricator should comment on concerns they may have about board warping 
and bowing, though
using thermal relief patterns or solid via hits probably will make very 
little difference; symmetrical
stackup and equalizing the copper coverage in the layers are the primary 
factors.  If and where you
use  only SMD parts, the thermal connection makes no difference in the 
solderability of those parts. 

However, if you cover the via openings at both ends with a solid polymer 
solder mask, it most
probably will be blown away during the assembly process as the trapped 
air expands.  I dont think
that thermal-relief connections would help with this.  So to me the 
first question seems to be: why
would you want to cover the via openings: any special reason?

Regards,

Istvan Novak
SUN Microsystems


ManatoshGBaidya@xxxxxxxxx wrote:
> Hi Steve,
> Thank you for your prompt reply.
> Here I am only concerned much about the Via through holes from Top to
> Bottom Layer. I using almost all of the SMD Components except few
> Through Hole Inductors & DC-DC Converter.
> You are right,Thermals create a amount of Resistance but is okay to me.
> I am not using Vias for Testing also. I am adding separate Test Pads.All
> of my vias are closed with Mask.
> If  I flood all of my vias rather than using thermal, will it cause any
> problem in the Assembling process. Will it pick heat through vias and
> circulate the same heat in all the plane layers due to flooding (Full
> contact with the Plane).Here Heat dissipation will not happen.Heat will
> spread out in all the Plane Layers.
>
> FYI.. Via size is small i.e 015 Inch Drill\.025 Inch Pad.
>
> Total amount of current I have right now is 1Amp.
>
> Pls advise me thereby
>
> Regards,
>
> Manatosh
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of steve weir
> Sent: Monday, March 02, 2009 11:40 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Advantages & Disadvantages of Flooding Vias??
>
> Thermal ties are appropriate when you want to limit the heat sinking,
> such as with a TH component lead, where excessive heatsinking will make
> reliable soldering and desoldering difficult to impossible.  Continuous
> pads are the norm for stitch vias.
>
> Typical thermal ties cover a minimum of 180 degrees arc.  For instance
> if your antipads are 0.035" 0.015" ties would cover 185 degrees arc at
> the outside of the antipad.  Are you sure that thermals insert too much
> resistance?  If they do, I would be concerned about the current carrying
> capacity of the via barrels.
>
> Steve
> ManatoshGBaidya@xxxxxxxxx wrote:
>   
>> Hi Gentleman,
>>
>> Good Morning.
>> I am working on a dense Aerospace Cockpit Control Board and I want to
>> Flood all of my Vias as Vias Connecting to the Respective planes
>> (Power & Gnd) is not having good connectivity through the Thermal
>>     
> Spokes.
>   
>> Flooding vias will help me gaining the required copper area for the
>> Circuit.
>> Via size used is .015 Inch Drill\.025 Inch Pad.
>> Will this create any problem in the Component Assembling Process as
>> some of the heat may pass through the planes and thus PCB may undergo
>> Bow & Twist or expansion of the PCB.
>>
>> Please put your expertise thoughts on it.
>>
>> Thank you,
>> Regards,
>> Manatosh
>>
>>
>>
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>
>
> --
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