[tinwhiskers] Re: - RoHS & BGAs!!!

  • From: Glen Herzog <gherzog@xxxxxxxxxxxxx>
  • To: "'tinwhiskers@xxxxxxxxxxxxx'" <tinwhiskers@xxxxxxxxxxxxx>
  • Date: Mon, 23 Feb 2009 16:08:08 -0600

Hani,

That question should get you a mixture of responses!  

Using SnPb solder on SAC balls, known as backward compatibility, tends to 
result in a product that may not be as reliable as either SnPb on SnPb or SAC 
on SAC.  However, when you know the environment that the product will see SnPb 
on SAC balls may yield quite satisfactory reliability.  For example if you are 
in a constant temperature, no shock, no vibration environment where a failure 
is not life threatening, SnPb on SAC may be satisfactory.  That is the mix that 
we have been using for several years and are satisfied.  We know that we will 
have to do lead free (someday) but for the time being we can afford to let the 
rest of the industry figure out which lead free it is going to be.

If you do consider SnPb on SAC I recommend a thorough literature search and 
some experimentation on your part.

Another note, SAC solder in combination with SnPb melts at 207C-208C.  So, add 
20C and you could solder at 225C to 230C and not stress the components so much 
and not grow as thick of an intermetallic layer.  You can get a good mix of 
solders at 220C and above.

Good Luck.


Glen Herzog
Quality Manager
Fairfield Industries
Ph. 281-275-7854
gherzog@xxxxxxxxxxxxx





-----Original Message-----
From: tinwhiskers-bounce@xxxxxxxxxxxxx 
[mailto:tinwhiskers-bounce@xxxxxxxxxxxxx] On Behalf Of AL-Yousef, Hani E
Sent: Monday, February 23, 2009 2:20 PM
To: tinwhiskers@xxxxxxxxxxxxx
Subject: [tinwhiskers] Re: - RoHS & BGAs!!! 

Bob & Ed,

Here is wild thought, since we are [the industry I am in] exempt from
having to comply with the RoHS initiative, whose to say that I can't use
eutectic solder [Sn/Pb] to solder the SAC BGA into the board.

Of course, given that the rest of the parts on the board can withstand
240C needed to melt the SAC balls. 

So I will use Sn/Pb solder at RoHS temperatures

Any thoughts on that!    
       

Thanks,
Hani

-----Original Message-----
From: tinwhiskers-bounce@xxxxxxxxxxxxx
[mailto:tinwhiskers-bounce@xxxxxxxxxxxxx] On Behalf Of Parnagian, Edward
Sent: Monday, February 23, 2009 11:53 AM
To: tinwhiskers@xxxxxxxxxxxxx
Subject: [tinwhiskers] Re: - RoHS & BGAs!!! 

Hani,

When Bob said "middle of the board is the worst" what he meant was that
midway between supports is worst.  If you're only anchoring at the
corners of the board, then the middle of the board is worst.  If you
have a support in the middle board, then half way between the middle
support and the surrounding supports is going to have the problems.

Best regards,
Ed

-----Original Message-----
From: tinwhiskers-bounce@xxxxxxxxxxxxx
[mailto:tinwhiskers-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Landman
Sent: 2009 Feb 22 4:51 PM
To: tinwhiskers@xxxxxxxxxxxxx
Subject: [tinwhiskers] Re: - RoHS & BGAs!!!

Hani,

Regarding underfill, if you do have to use SAC then underfill does seem
to help (depending on where on the board the BGA will be located (in the
middle of the board is the worst place - where mechanical stress is
greatest).  This article is a good one on the subject

http://ap.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subs
ection=Display&ARTICLE_ID=220942

Bob Landman
H&L Instruments, LLC




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