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Reply To: | TechNet E-Mail Forum. |
Date: | Fri, 3 Aug 2001 12:41:06 +0200 |
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Hi Bill,
It looks bad.The solder on those pads is heavy contaminated prior to wave
soldering.
You should examine unprocessed boards.This kind of appereance might be
results of lot of things:
- incident splash of chemicals corrosive to tin/lead ( for example those
based on sulfuric acid) somewhere between HASL and your assembly line.
- unwashed chemicals from HASL precleaning line
- poor etch resist removal ( tin or tin/lead from pattern plating)
-dross in HASL pot
- rework ? ( results of unwashed aggresive flux used for rework)
I do not think,that this is results of LPI residues - if those are present
on the pads,the result is lack of coverage
Edward
Edward Szpruch
Eltek , Manager of Process Engineering
P.O.Box 159 ; 49101 Petah Tikva Israel
Tel ++972 3 9395050 , Fax ++972 3 9309581
e-mail [log in to unmask]
> -----Original Message-----
> From: Stephen R. Gregory [SMTP:[log in to unmask]]
> Sent: д аевеси 02 2001 17:45
> To: [log in to unmask]
> Subject: Re: [TN] Process Problem vs Board Problem
>
> Hi Bill!
>
> In looking at the pictures, I must say that the HASL does look kind of
> strange. It almost looks like the HASL is just adhered in that ring around
>
> the pad, and the rest of the pad and barrel almost looks like tin with no
> HASL covering?!?
>
> Do you remember if the boards looked the same back when you had no
> problems
> as they do now?
>
> Maybe somebody else has a clue...
>
> -Steve Gregory-
>
>
>
>
> Technetters'
>
> I've recently run into a problem with Wavesoldering some circuit
> boards
> where I am having problems getting topside solder joints. The
> process that
> I'm running has the topside of the board at 195-200 F just prior to
> the
> solder wave. My conveyor speed is 4.0 fpm. My fluxer is a spray
> fluxer. The
> board is a .062 - 6 layer board that has an aluminum heat sink on
> it. I feel
> that my process is set correctly.
>
> The original process that previously used on these boards was very
> successful when we used an OA water soluble flux. This process was
> on that I
> qualified many years ago to J-Std-001A for Class 3 assemblies.
>
> On these circuit boards, I'm trying to use a No Clean Lo Activity
> level flux
> that is water washable. Because I have new equipment for
> wavesoldering, I
> was hoping to not have to do a re-qualification process for our
> level 3
> assemblies. Because our new equipment has much better controls than
> our old
> equipment I thought that it would be easy to solder these boards
> with an LO
> active flux. Well, my initial pass has been a disaster so far. There
> are
> three pictures that I'm looking for comments on. They are located on
> Steve's
> Webpage at http://stevezeva.homestead.com. (A thousand thanks go out
> to
> Steve Gregory for providing a site for posting the pictures.) Two of
> the
> pictures, called Bare Pad and Bare Pad2 show a condition that I can
> describe
> but I don't know if this condition has a name. In those pictures,
> there is a
> heavier coat of solder on the pad, but it seems to form a concentric
> ring on
> the pad.The extremities of the pads, both toward the outside and the
> inside,
> show a tinned surface but it appears to be much thinner. To me, it
> seems
> like these thin areas do not readily solder. It seems like this thin
> area is
> barrier that can only be overcome with a very strong OA flux. This
> may
> explain why I did not have a problem before. The other picture shows
> another
> condition that I see in various places on the bare board where there
> are
> protrusions on the inside of the PTH's. This appears to be trapped
> volitiles
> that were being expulsed during the HASL process.
>
> I'm trying to determine if I have a board problem or a process
> problem.
>
> Is it unreasonable for me to think that this board can be soldered
> with a
> no-clean (but water washable) LO activity level flux?
>
> Any help or comments would be greatly appreciated.
>
> Bill Kasprzak
> Moog Inc., Electronic Assembly Engineering
>
>
>
>
>
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