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Subject:
From:
Victor Hernandez <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 2 Oct 2013 06:08:31 -0500
Content-Type:
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text/plain (146 lines)
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]

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