Doesn't the original mail say it returns to flat when cool? So the issue may
not be residual stress just the shape/config causing it to bend when heated.
If it is flat at room temp, is there a case for saying does it matter [like
Bev said]. If it works as a shield and withstands drop test then I guess it
doesn't. You would have an issue with discretion on inspection though so in
that sense you might need to resolve it.
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Thursday, July 07, 2016 2:23 PM
To: [log in to unmask]
Subject: Re: [TN] Shielding cans deformation during reflow
simulated reflow... use what ever your process window. measure flatness
before and after. you need to establish what your tolerance you can handle.
make sure you get sufficient sample size and sheet metal rolling direction
sort out (not cheap... but cheaper than you trouble shoot or rework at MFG
site... your design determine the cost.. if they skip qual, you pay 10x at
assembly line. trade off using process window adjustment - such as extend
Tp, you might get other issues - some of the device may got damaged = e.g.
highend of chips may have limited temp you can be exposed to). good luck.
> I also suspect that it caused by stress release. The shield may have
> residual stress, when go through high temperature, metal yield
> strength go down and make shield deformation.
> Is there more information about the qualification process?
> Best regards
> -----Original Message-----
> From: Yuan-chia Joyce Koo [mailto:[log in to unmask]]
> Sent: Wednesday, July 06, 2016 6:56 PM
> To: TechNet E-Mail Forum <[log in to unmask]>; Deng RongJun
> <[log in to unmask]>
> Subject: Re: [TN] Shielding cans deformation during reflow
> residual stress. design and MFG issues. you should have co-
> planarity in dwg and spell out user condition before and after reflow
> simulation as part requirement. and go through qualification process
> before hit production... a vendor selection problem.
> On Jul 6, 2016, at 2:39 AM, Deng RongJun wrote:
>> Hello fellow Techies,
>> I have got a problem with shielding cans deformation issue. There are
>> several kinds of shielding cans on board, we have found one shielding
>> have deformation after reflow, one side of shielding lift and not
>> solder on board.
>> We also do a test, bake the individual shielding in oven with 230
>> degree, the shielding still have deformation and two corner have lift.
>> Take out the shielding from oven and temperature go down, then
>> shielding go back to good.
>> Any one of you have experience on this case?
>> Thank you very much.
>> Best regards