Hi,
The following is not exactly a "Rigorous" description, I would appreciate
and additional comments.
ImSN is simply tin. HASL is solder and it typically thicker. My observation
is both tin and HASL will form oxides but tin does so faster and the oxides
on InSN do not wet as easily as a HASL surface. (Can anyone confirm / deny
this?). With HASL the layer of solder melts during reflow and mixes with the
applied solder. Oxides on the HASL surface are mechanically moved.
With ImSn the oxides are firmly on the surface, flux must remove them
chemically before a wetting process can take place.
It is one thing to have a thin layer of metal to which solder can flow and
attach while it is another thing to already have solder on the board.
Solder doesn't "Solder To" HASL. HASL is solder. It has been my experience
nothing solders better than Solder.
Now of course there are a lot of different solder types, and if solder is
completely removed from a pad leaving behind an inter-metallic surface then
that surface is no longer "Solder". I am biased towards HASL, it has simply
worked out so well for me. It is not "Flat" but who cares after the paste is
printed. And I have never see a board with ALL the solder removed.
I still don't understand why folks would use InSN when they could have used
HASL? Please explain. (Other than InSN is FLAT.)
Thanks,
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Wednesday, October 02, 2013 7:09 AM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Folks,
I has a similar experience in which I questioned the use of HASL or ImSn
and did not receive any feedback. What is the difference between ImSn and
HASL besides the volume of solder left on the pads.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Wednesday, October 02, 2013 5:45 AM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Hi Steve-
From these limited pictures, the finish looks like ImSn: On the solder
sample picture, the parts of pads not wet by solder look matte to me. On
the close-up of the original picture, the "tarnish" area is more likely
copper being exposed as the thin layer of ImSn gets sucked into the solder
joint. (ImAg does the same thing if you don't have the right profile.)
If the pads on the boards "as delivered" are matte white, you're dealing
with either ImSn or ImAg. But most ImAg formulations wet a lot better than
most ImSn formulations because, as noted many times on this forum, Ag oxides
are easy to solder to, but Sn oxides can create lots of problems. However,
Ag oxides are visually trivial to detect, so if you wrap a fresh board up
with a peeled hardboiled egg, then you'll know in a few hours whether the
finish is ImAg.
Since Pb free HASL deposits mostly Sn, it may be difficult to discern
whether you're dealing with ImSn or HASL unless the finish is matte.
(Bright Sn plate is usually even less desirable than matte Sn since it grows
whiskers the fastest.) A cross-section should show a "considerable"
thickness of Sn if the finish is really HASL (>5 microns). I can't remember
if IPC specs have a minimum thickness for HASL coating--it's a finish I only
use rarely. And, of course, HASL should show "puddling".
An interrupted ENIG would usually have enough Ni on it that you could
clearly see it in a cross-section at around 200X. And, of course, there are
several analytic techniques and instruments available at external labs to
see whether you are looking at Sn or Ni.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 01, 2013 7:14 PM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Okay here's another picture. I printed a solder sample and sent it through
the oven and this is what it looked like:
http://stevezeva.homestead.com/SolderSample.jpg
You can see all the non-wetting going on. The board was profiled and it was
fine. We are using a FCT Assembly WS889 SN100C solder paste.
What is even more strange is that the first side of the board looked okay,
but the second side looks like in the photos, like the problem is confined
to one side of the board if that's possible.
The solder sample was only reflowed once, but I printed the paste on the
side that was to be built last. Weird huh?
I know you can't tell anything for sure just from some photos, but it's the
strangest thing I've seen in a while...
Steve
-----Original Message-----
From: Steve Gregory
Sent: Tuesday, October 1, 2013 4:46 PM
To: [log in to unmask]; Steve Gregory
Subject: RE: [TN] HASL question
Here's one picture:
http://stevezeva.homestead.com/NonWetting.jpg
Look at the left pad and the tarnish that you see there, does that look like
tarnished nickel?
This is after the board was washed. I have places all over the board that
looks like this.
I'll post a picture of what it looks like after I printed a solder sample
with paste and sent it through the reflow over
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 1, 2013 4:16 PM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Ahhhh....it's what I figured. I think that's what happened. I'll have
pictures later.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Tuesday, October 1, 2013 4:15 PM
To: [log in to unmask]
Subject: Re: [TN] HASL question
No. Not unless somebody screwed up.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, October 01, 2013 6:11 PM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Hi all,
It's funny that the HASL topic has come up today, because we just ran a
board today that supposedly was lead-free HASL finished, and man it looks
like crap!
Question; does a PCB get nickel before it gets Lead-free HASL'ed?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev.
PhD
Sent: Tuesday, October 1, 2013 2:23 PM
To: [log in to unmask]
Subject: Re: [TN] HASL question
Hello Victor,
It wouldn't solder in a first place.
--
Best regards,
Vladimir Igoshev. PhD
mailto:[log in to unmask]
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask]
______________________________________________________________________
|
