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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 22 Mar 2006 09:08:42 -0600
Content-Type:
text/plain
Parts/Attachments:
text/plain (357 lines)
Hi Dale - the shrinkage voids and SNIC (aka. Sn100C) make for great
discussion. As an FYI the JCAA/JG-PP No-Lead Solder Project consortia work
has just finished up and will be giving an industry report out on April
4th. I am way too biased (Rockwell Collins was a consortia participate) but
I think the test results will be very useful to the industry. The testing
consisted of IPC Class 3 testing of 3 Pbfree solder alloys (SAC, SACB,
SNIC, SnPb control)  in vibration, thermal shock, thermal cycle (two
temperature ranges), mechanical shock and HALT. Some of the test result
data is applicable to the questions/discussion that Phil, Amol, and others
have highlighted. The weblink to the project is:

http://acqp2.nasa.gov/LFS.htm

I'll apologize in advance if someone construes this email as a commercial -
the JCAA/JG-PP No-Lead Solder project test results are available to the
electronics industry as a data set to assist folks trying to understand
Pbfree solder implementation aspects from a IPC Class 3 testing sequence.

Dave Hillman
Rockwell Collins
[log in to unmask]



                                                                       
             Dale Ritzen                                               
             <[log in to unmask]                                         
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             Sent by: TechNet          [log in to unmask]                 
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                                                                   Subject
             03/22/2006 08:48          Re: [TN] Microcrack Link        
             AM                                                        
                                                                       
                                                                       
             Please respond to                                         
              TechNet E-Mail                                           
                   Forum                                               
             <[log in to unmask]>                                         
             ; Please respond                                          
                    to                                                 
                Dale Ritzen                                            
             <[log in to unmask]                                         
                   COM>                                                
                                                                       
                                                                       




Thanks Amol,
I would be interested in seeing what comparable solder junctions look like
with the Sn100c alloy. Do you, or anyone else on TechNet for that matter,
have comparable pictures of Sn100c joints? I saw some in a Circuit Assembly
article that David Suraski sent a link for yesterday, but I haven't seen
many more than that. However, after what I saw in that article, I am having
serious doubts about using SAC305 for PTH applications (i.e. solder wave,
pots, hand soldering, etc.), especially since it doesn't have near the
corrosive affect on metals like SAC305 purportedly does. And the solder
junctions look extremely good even though the shearing force data looks a
tad worse than with SAC305.

Anyone care to jump in here with more opinions about Sn100c use in the PTH
world? If there is anything in this regard in the Lead-free forums, please
let me know and I'll have a look there. In the past I haven't been
successful in finding many things in the various forum archives...

Thanks!
Dale Ritzen
Quality Manager
Austin Manufacturing Services

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kane, Amol (349)
Sent: Wednesday, March 22, 2006 7:49 AM
To: [log in to unmask]
Subject: [TN] Microcrack Link


Here is the image

http://img2.uploadimages.net/show.php?img=268781Microcrack.jpg


Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]

 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Kane, Amol (349)
Sent:   Wednesday, March 22, 2006 8:26 AM
To:     [log in to unmask]
Subject:        Re: [TN] mixing lead-free solders

Sure can,
Microcracking occurs to the mechanics of cooling of SAC305 alloy. To
explain
crudely, During cooling, Sn dendrites are formed starting from the barrel
to
the fillet surface. The remaining liquid alloy is then sucked into the
spaces between these Sn dendrites. Concurrently, the substrate expands as
it
goes over the wave, and contracts when it cools. This creates stress in the
joint when the solder is cooling. Due to this we see fissures in the fillet
surface that is the last to cool (usually the bottom fillet)

I have an x-section picture of a microcrack...will upload it and post the
link on the forum. IPC 610RevD says that the joint is acceptable if (a) the
bottom of the crack is seen and (b) the crack does not touch the lead or
the
land

The problem is, you cannot see the bottom of the crack in the
magnifications
mentioned in IPC, and even if you can, the fissures do not form linearly
into the fillet (the picture will make this statement clearer), and hence
you may not be seeing the "true" bottom. IPC 610 Rev D tries to address
this
issue based on the info the industry as a whole has. Changes will occur to
it in the future when more data is available, but for now we have the
standard to go by.

I x-sectioned the joint and also x-rayed it to determine the extent of the
crack in the fillet. Then based on a sampling plan, I am going to x-ray 'n'
boards and if they are defect free, shall pass the lot. But do I want to
keep doing this on lot of board I produce on the wave in the future?


Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing
941 Route 38  Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]

 -----Original Message-----
From:   TechNet [mailto:[log in to unmask]]  On Behalf Of arnaud grivon
Sent:   Wednesday, March 22, 2006 8:11 AM
To:     [log in to unmask]
Subject:        Re: [TN] mixing lead-free solders

Amol,

Could you expand on the kind of defects you experienced (cross section
pictures) and clarify your "testing was a hassle" statements?

Phil Nutting a écrit :
> Thanks Amol.  I'll look at this more closely.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
> Sent: Wednesday, March 22, 2006 7:17 AM
> To: [log in to unmask]
> Subject: Re: [TN] mixing lead-free solders
>
> Hi Phil,
> Based on the info in the e-mail, you say you are using SAC305 in the
> wave.......did you do any testing that proved that SAC305 was superior
> than SN alloy in wave? Or is this an absolute requirement for the
> product/process?
>
> We used SAC 305 in wave and ended up with Hot Tears on greater than 90%
> of all TH joints........you may have the following issues
>
> 1. if you get hot tears, current IPC spec is not sufficient to pass/fail
> them (because it is impossible to see the bottom of any of the tears @
> magnifications mentioned in IPC 610)
> 2. I did some X-sectioning and X-ray analysis of our samples, and even
> though they turned out OK as per IPC, testing them was a hassle to say
> the least.
>
> So be careful before using SAC305 in wave.
>
> Good Luck
>
> Amol Kane
> M.S (Industrial Eng.)
> Process Engineer
> Harvard Custom Manufacturing
> 941 Route 38  Owego, NY 13827
> Phone: (607) 687-7669 x349
> [log in to unmask]
>
>  -----Original Message-----
> From:   TechNet [mailto:[log in to unmask]]  On Behalf Of Whittaker, Dewey
> (AZ75)
> Sent:   Tuesday, March 21, 2006 4:36 PM
> To:     [log in to unmask]
> Subject:        Re: [TN] mixing lead-free solders
>
> I've seen several presentations that shows that to be an effective
> combination. All other things being equal, you should be fine.
> Dewey
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Nutting
> Sent: Tuesday, March 21, 2006 2:07 PM
> To: [log in to unmask]
> Subject: [TN] mixing lead-free solders
>
> Good afternoon,
>
> As we move further into LF conversion I was curious what you, the gurus
> of TechNet, thought about the possibility of mixing LF solder alloys.
>
> We are converting our manufacturing operation to SAC 305 for wave and
> hand solder.  We have a CM that is using Sn100C in their wave.  There is
> the potential to have to manually repair a board built with Sn100C by
> hand soldering with SAC 305.  Are there any reliability issues with
> this?  Assume the board will be properly cleaned after soldering.
>
> I haven't looked into our SMT CM and their process, but it could be
> similar.
>
> I'd hate to have to run three or four lines to keep each alloy separate.
> As it is I must manage Sn/Pb and SAC 305.
>
> Thanks in advance.
>
> Phil
>
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