Mike;
I have same opinion of Ioan with item number one.
For item number two search technet archives for " exposed copper " and you
will see that is a condition accepted for vertical conductor edge, but
generally all surface from OSP boards are wetted by the solder paste and
exposed copper isn't common.
Bellow is a copy/paste from a related question in the paste:
Craig,
See IPC-A-610B Rev B, Section 4.2.1, 'Exposed Basis Metal'. There is
a note that addresses OSP and exposed copper. Even without applying the
note, it is still considered only a process indicator rather than a
nonconforming defect.
If you are already working to the new release of IPC-A-610C, it is
covered in better detail in Section 6.5.2, 'Exposed Basis Metal'.
Mike McMonagle
PCBA Process Engineering
Telxon Corporation
(713) 307-2443 Phone
(713) 307-2581 Fax
www.telxon.com
' Innovative Solutions for
Mobile Information and
Wireless Communications'
-----Original Message-----
From: Craig Leppanen [mailto:[log in to unmask]]
Sent: Thursday, April 27, 2000 7:47 AM
To: [log in to unmask]
Subject: [TN] spec for exposed copper
All-
I have a situation on an SMT OSP board. There is some exposed copper on the
periphery of fine pitch lands. The lands have greater than 85% solder
coverage
and acceptable joints. But the customer is concerned about the exposed
copper.
I have not seen a spec explicitly stating that exposed copper on an OSP
board is
acceptable. Does such a spec exist??
Thanks, Craig Leppanen
For item number 3 the OSP will be degraded at the first pass at reflow
temperature and soldering will be more hard next time.
I hope this help
Jorge Dourado de Santana
Maintenance / Process Engr
Microtec - Brazil
> -----Original Message-----
> From: Tempea, Ioan [SMTP:[log in to unmask]]
> Sent: 8 de Maio de 2000 13:36
> To: [log in to unmask]
> Subject: Re: [TN] OSP and Fine Pitch
>
> Mike,
>
> can't help you with the OSP-HASL dilemma, but as far as the printing is
> concerned, I would look at something else that generates the shorts. We
> are
> using on some fine pitch even 100% aperture (0.012" for .020" pitch) and
> still have no shorts. The apertures you mention are OK, you shouldn't
> blame
> the shorts on them.
>
> There are a few major things you should consider:
> - the printer itself; does it perform the alignment stencil-PCB
> automatically, or the alignment is done manually. Manual won't get you rid
> of shorts, no matter what you do!
> - have the operator wipe the fine pitch area on both bottom and the top of
> the stencil every 5th or 6th board
> - the paste itself: powder size, how long out of the fridge, etc
> - printing speed
> - snap-off and squegee pressure
> - you mean shorts after print, or after reflow? If you see them after
> reflow
> and not after print, maybe you manipulate the boards too much, or check
> the
> insertion and manual correction.
>
> Hope this helps,
> Ioan
>
> > -----Original Message-----
> > From: Mike Lang [SMTP:[log in to unmask]]
> > Sent: Monday, May 08, 2000 10:26 AM
> > To: [log in to unmask]
> > Subject: [TN] OSP and Fine Pitch
> >
> > Hi gang,
> >
> > A few general questions regarding fine pitch SMT assembly:
> >
> > 1) My research indicates the "industry starting point" for fine pitch
> > (0.020" pitch) solder pad and stencil design is 0.012" wide PCB solder
> > pads and 0.010" wide laser cut stencil apertures in 0.005" or 0.006"
> thick
> > stencils. I find that using these parameters I still tend to get some
> > solder shorts. Any comments about better pad / aperture designs?
> >
> > 2) I am using HASL, but recognize the benefits of going to OSP (flatter
> > among other things). My concern is the bare copper left on the PCB
> since
> > the paste does not fully wet out the pad. Does anyone have comments, or
> > better yet, test data which demonstrates what is acceptable?
> >
> > 3) Another HASL / OSP concern... PCB is double sided reflow using no
> > clean, and then has a small quantity of hand soldered (GASP!) through
> hole
> > components assembled. Will the PCB remain solderable for hand soldering
> > after 2 reflow cycles? Again, I expect bare copper in places since the
> > solder will not naturally flow out to cover all surfaces of the hand
> > soldered pad, top and bottom, especially after two reflow cycles.
> >
> >
> > Thanks!
> >
> > Lang
> >
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