Another phenomena that can happen with soldermask fillers is something that
you see here:

 http://stevezeva.homestead.com/ZebraStripes.jpg

This is a board that came out of a inline DI board wash with the stripes
that you see that matches the mesh conveyor links. Technet gurus Brian
Ellis and Bill Kenyon posted this a long time ago:

Brian Ellis: "There are a number of potential causes. A common one is
the exposure of
solder mask fillers because the cleaning removes the surface molecules
of the solder mask. This is largely cosmetic but it may mean the mask is
insufficiently cured. As you state (or I did in the earlier exchange!),
heat will allow the filler to sink in."

Bill Kenyon: "Quick identification of the (solder mask) residue- if it
is the white
powder fumed silica used to thicken liquid solder masks, you will often
see it appear as Brian has noted. If the solder mask is undercured, any
cleaning step may strip off part of the green solder mask, exposing the
white thickener powder (typical trade name is 'Cab-O-Sil"). Heat the
white area with a heat gun. If the residue is the Cab-O-Sil, the heat
softened solder mask will allow the Cab-O-Sil to sink back into the
green solder mask.
Residue disappears, problem is insufficient UV cure during solder mask
processing."

And yes, applying heat did cure the stripes. Baked the boards in a
oven for about 1/2 hour and the stripes went away...

Steve


On Tue, Feb 28, 2017 at 7:20 AM, Stadem, Richard D. <
[log in to unmask]> wrote:

> While it is possible that some level of cabosil or other ground silica
> filler product may be added to the prepreg resin, I would be very, very
> careful of going down that path. Once again, you do not get something for
> nothing. Extensive qualification would be required for such a change. The
> insulative, dielectric, thermal expansion (CTE), thermal radiation, and
> many other properties would see a radical change if the laminate resin
> properties changed. Issues such as the ability to be drilled, drill wear,
> router wear, the ability for drilled holes to be plated through (bond
> strength of plated copper to the hole wall, moisture absorption (or lack
> thereof), glass transition (Tg) and damage point (Td) temperatures,
> resistance to CAF formation, flux entrapment, thermal dissipation
> properties, solder mask bonding, clad copper foil bonding strength, there
> are so many that would need to be qualified and studied. Is there a
> compelling reason you would want to do this? I'm not saying it is a bad
> idea, I am just saying proceed with extreme caution.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of
> [log in to unmask]
> Sent: Tuesday, February 28, 2017 8:07 AM
> To: [log in to unmask]
> Subject: [TN] LF Laminates, Resin Fillers
>
> Dell - Internal Use - Confidential
>
> Bhanu,
>
>     Thank you for sharing.....   I hope that other forum gurus will chime
> in on my laminate resin inquiry.
>
> Victor,
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bhanu Sood
> Sent: Monday, February 27, 2017 1:57 PM
> To: [log in to unmask]
> Subject: Re: [TN] LF Laminates, Resin Fillers
>
> No.
> For a resin matrix used in e-glass reinforced laminates (e.g. FR4), adding
> spherical glass fillers creates too many opportunities for reliability and
> quality issues.
>
>
> On Mon, Feb 27, 2017 at 9:50 AM, <[log in to unmask]> wrote:
>
> > Fellow TechNetters:
> >
> >    Can the laminate resin incorporate round/sphere glass media filler?
> >
> > Victor,
> >
>
>
>
> --
> Bhanu Sood
> Tel: (202) 468-8449
>

-- 


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