Hi Werenr,
Very good advices.
You are absolutely right about how to correlate the measured strain range or energy accumulated in one cycle to the mean fatigue life of the package(discountiniuty test).But isn't it what we always do if we are not using FEA.
I am measuring the total strain at the selected joint.I will generate the loops for creep strain based on a constitutive model.
The tests are performed from RT to 125 oC same as ATC.
I used to generate loops from the beginning of the cycles until reaching the stabilized one.But this time I decided to cycle the package first for some cycles, then measure strain of critical joint only for one cycle.
So I was after to know maybe after how many cycles for this type of the package I may reach to stabilized cycle or saturated state cycle?
I usually experienced three to four cycles for other types.But I just wanted to be sure for this type.
I guess you suggest the energy-based based on what I understand.
Thanks,
Al
--- On Fri, 6/19/09, Werner Engelmaier /* <[log in to unmask]> wrote:
From: Werner Engelmaier /* &[log in to unmask]>
Subject: Re: [TN] [TN
To: [log in to unmask]
Received: Friday, June 19, 2009, 1:18 PM
Hi Al,
How to you relate strain measured on the package to the strain in the solder joints? What do you mean be "saturated state cycle"?
The strain range is only a adequate measure under some circumstances, but not all—in others you also need the stress range.
I suggest you follow the procedures in IPC-D-279.
Werner
-----Original Message-----
From: al shirazi <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Jun 19, 2009 11:38 am
Subject: [TN]
Dear TechNeters,
I am measuring strain of a corner joint of a lead-free Lidless FC-PBGA
package.For the purpose of looking into the fatigue life of the joints under
thermal cycling (ATC profile).
Is recording strain for one cycle after cycling the package for some cycles is
good enough to be referred as the saturated state cycle?After how many cycles
maybe for this type of the package?Any previous experience?
I appreciate your inputs from either experimental point of view or modeling,
Thanks
Al
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