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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Thu, 16 Apr 2009 14:06:51 -0500
Content-Type:
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text/plain (242 lines)
Refer to this article in the October '08 issue of Circuits Assembly.
http://www.circuitsassembly.com/cms/magazine/198/7205-october-2008-issue
.

LGAs should not be used "as is" for military or high-reliability
applications.
If you want to get compliant leads or solder balls attached to an LGA or
BGA, I suggest you have someone like Analog Technologies do it with
their laser attachment process.
They use a laser soldering machine they developed along with a
proprietary qualified process to do the ball or compliant lead
attachment. Their process does not use nitrogen, but uses a special
anti-oxidizing compound that leaves an amazingly pristine solder sphere
or solder joint. The BGA or LGA component body never gets hot during the
ball/lead attach process; they embedded thermocouples in the component
body, and measured a 1 degree C. increase from ambient during the laser
soldering process.
The solder spheres or compliant leads are heated from the inside out.
Provided the component is later soldered to the PWB using a good, well
controlled conventional convection process later, the mean time before
failure is nearly doubled for BGAs, and for LGAs with compliant leads or
columns the number of cycles to failure can be extended up to 10 times
that of the same component soldered directly to the PWB.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee Whiteman
Sent: Thursday, April 16, 2009 10:06 AM
To: [log in to unmask]
Subject: Re: [TN] LGAs in a military environment?

Wayne,

Be careful about making this type of part a BGA through re-balling. We
tried that with a similar package (not as many I/O). To get the balls to
solder to the component, the refinishing supplier over heated the
components, destroying much of the lot.

I would prefer to have it packaged as a BGA instead of trying to fix it
into a BGA scheme via refinishing.

Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne
Sent: Thursday, April 16, 2009 10:47 AM
To: [log in to unmask]
Subject: Re: [TN] LGAs in a military environment?

Why aren't these parts BGA's anyway?  Is it just the extra inductance?
Or is it because putting on solder balls costs money?

I'd send them out and get real balls put on them.  You may need to limit
the solder joint height due to potential parasitic issues, but I'm
guessing that 0.15mm (6mils) joint height would not kill the performance
and would substantially improve all aspects of reliability.  (Underfill
may be required to achieve thermal rqmts)

Wayne Thayer



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Temkin, Gregg
Sent: Thursday, April 16, 2009 10:29 AM
To: [log in to unmask]
Subject: Re: [TN] LGAs in a military environment?

Our failures were by analysis only.  We did not go into production with
these parts. We were evaluating the fatigue reliability of the solder
joints.  We tend to be very conservative in our design approach, but we
have to be, since we're building hardware that controls the primary
power systems in aircraft. We also have generally steered away from QFN
parts for the same reasons.

At my former employer we designed a product with QFN microcontrollers.
We had a very high percentage of failed solder joints after ESS.  That
company's quality systems and ethics were pretty sketchy, so the parts
would go through a rework cycle and if they passed ESS after that, the
product was shipped.  No cause was assigned, everything was considered
an "isolated failure". That product hasn't yet made it to the field
(tied to a long development military helicopter program) so the field
failure rate is yet to be seen, but it's obviously not going to be good.
Fortunately it's not too critical a piece of hardware.

Gregg


-----Original Message-----
From: kwood716 [mailto:[log in to unmask]]
Sent: Thursday, April 16, 2009 6:40 AM
To: 'TechNet E-Mail Forum'; Temkin, Gregg
Subject: RE: [TN] LGAs in a military environment?

Gregg,
What were the failures? I'm interested because I see LGA usage picking
up steam here.
Ken



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Temkin, Gregg
Sent: Thursday, April 16, 2009 9:22 AM
To: [log in to unmask]
Subject: Re: [TN] LGAs in a military environment?

We just designed out similar LGAs made by Linear when a reliability
analysis showed VERY EARLY failures probabilities for our typical
operation cycle over a 20 year life.

You can certainly get them soldered and have them pass a screen but that
may not be the whole picture.  Depends on your operating
environment/life requirements.  Suggest having someone who is good at
analysis run the numbers.

Gregg

-----Original Message-----
From: Graham Collins [mailto:[log in to unmask]]
Sent: Thursday, April 16, 2009 3:32 AM
To: [log in to unmask]
Subject: [TN] LGAs in a military environment?

Hello Technet!
One of our designers is advocating using a LGA component in a military
product.  Anyone out there doing it?  I'm wondering (worried) about the
reliability since it has a very low standoff.  And cleaning issues?

An example of the parts I'm referring to:
http://www.linear.com/designtools/packaging/lga/05081807_a_lga66.pdf
A Linear Technologies p/n LTM4604

regards,

Graham Collins
Halifax Production Engineering
(902) 873-2000 ext. 6215


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