Tri
Very little scientific work has been done on this. The original doc taking figures out
of a hat for G-10 laminate was MIL-P-275x, now, I think, partially incorporated into
IPC-P-275x but, to the best of my knowledge, there has been little more recent done
than this 30+ year-old data, which applies to all applications.
In 1988, I published a paper giving evidence of reversible ion migration within FR-4
laminates at voltage gradients as low as 10 V/mm with recovery times of several hours.
This does not mean that they should not be used at such gradients for most
applications, but at 100 V/mm there was some small evidence of permanent changes. My
feeling is that, above this, there could be a risk.
Brian
Le Dai Tri wrote:
> Dear Brian,
>
> Could you tell me specific voltage gradient spec. for each kinds of PWB:
> handheld, consumer, mother board ...?
> Which document may I refer ? (IPC, MIL ...)
>
> Best regards,
> Tri'.
>
> ----- Original Message -----
> From: Brian Ellis <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, June 22, 2000 6:08 PM
> Subject: Re: [TN] Electrical testing of bare board
>
> > Howard
> >
> > I presume by 3,5 mil, you mean 0,0035", equivalent to about 80
> micrometres. Putting 250
> > V across this, with or without mask, gives a voltage gradient of about
> 3000 V/mm which
> > is HORRENDOUS. A typical acceptable voltage gradient without mask is about
> 100-150
> > V/mm, maybe double that with mask, if all the best conditions are united.
> If your
> > substrate has absorbed any humidity (and it is likely that it will have
> done), you will
> > be pulling apart any ionics in the material. At the best, you will damage
> it. At the
> > worst, it will simulate an arc welder. Please don't do it.
> >
> > Brian
> >
> > Howard Lin wrote:
> >
> > > Hi TechNetters,
> > >
> > > We do some testing of bare board right now. Can anyone point out what
> > > different between board with solder mask and without solder mask on
> > > electrical testing process? If we apply 250 voltage on 3.5 mil spacing
> > > pattern , will it damage electrical character? Is there copper migration
> > > occuring during 250 voltage testing?
> > >
> > > Howard Lin
> > >
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