Bev's assessment is right on.
The particular component that Graham's designer wishes to use is a real
"problem child" from a long term reliability standpoint, not only
because of the fact that it is an LGA with very large delta CTE between
component and substrate, but also from the standpoint of having a lot of
connections underneath, which reduces cleanability even more.
And no-clean fluxes typically don't completely activate underneath a
package of this type, even if it were able to be used.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Thursday, April 16, 2009 9:58 AM
To: [log in to unmask]
Subject: Re: [TN] LGAs in a military environment?
Graham,
For your use, I would avoid them. Cleaning would be a really struggle
and I doubt you are using no-clean solder paste. They were designed for
people like us - thin, "sexy" products. They work, but I hate them too
- you can't generally use underfill and solder joint voiding is a
problem.
Bev
RIM
-----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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