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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