When I worked as SQE at a large Corporation, we required 100% plugging of vias prior to HASL.  When the
vias were plugged with mask after HASL, the solder in the vias would become molten during assembly
operations and create solderballs and volcano looking eruptions that occasionally shorted to the
component.  This was more likely to happen when there was a fair amount of solder in the holes.
Unfortunately, keeping the solder at a minimum lead to intermetallic only and solderability issues on SMT
pads ... the board fab shops were between a rock and a hard place ... HASL thickness just isn't
controllable to the degree needed to prevent both the solderballs and the intermetallic only SMT surfaces.

We required 100% plug because the assemblies went into highly corrosive environments and bare copper was
unacceptable.  We also had concerns about entrapping flux under components especially if the vias were
plugged from the bottom side.

Two suppliers were able to provide us with 100% plugged vias that met our requirements consistently.  They
developed reliable and repeatable processes.  The plugged vias also did not pose problems in SMT assembly
since the height was also controlled.

Marti Tully

Martin, Jesse wrote:

> Our fab vendor refuses to plug any via greater than .015". The most common
> problem we see with plugged vias is excess height causing screen printing
> problems. We also see solder balls forming on the top side of the board when
> the bottom side is reflowed. Our vendor attributes this to the plugged vias.
> Needless to say we're making every attempt to do away with the plugs
> whenever possible.
>
> > -----Original Message-----
> > From: [log in to unmask] [SMTP:[log in to unmask]]
> > Sent: Thursday, September 24, 1998 7:59 PM
> > To:   [log in to unmask]
> > Subject:      [TN] Help! Plugging vias
> >
> >
> > <Original text message attached as document>
> >                                     << File: ceomail.wrd >>
>
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