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Subject:
From:
Curt McNamara <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Curt McNamara <[log in to unmask]>
Date:
Thu, 21 Apr 2016 09:50:12 -0500
Content-Type:
text/plain
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text/plain (124 lines)
Thanks to everyone! We have cleared out the layout in the corners to allow
for staking. Seems like a good compromise.

Can anyone suggest a reference / recommendation on best practice for corner
staking?

            Curt

On Wed, Apr 20, 2016 at 9:31 AM, David Hillman <
[log in to unmask]> wrote:

> I agree with Dwight and Todd - a Wafer Level CSP (WLCSP) is really a flip
> chip device (silly marketing definitions - just causes confusion!) so
> without the application of an underfill material, there are going to be
> solder joint cracks/failures unless the product use environment is really
> benign.
>
> Dave
>
> On Wed, Apr 20, 2016 at 9:17 AM, Mattix, Dwight <[log in to unmask]>
> wrote:
>
> > S/M define pads on a ball and no underfill or corner staking?   Standby
> > for cracked solder joints.
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of MacFadden, Todd
> > Sent: Wednesday, April 20, 2016 5:10 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] .031 PCB and WLCSP
> >
> > Without underfill in this application your greatest challenge for solder
> > joint reliability will likely be from drop rather than cyclic strain and
> > fatigue. It's a small device (9x9mm) so that risk may be relatively low,
> > but here are some things you may consider:
> >
> > * PCB-side solder joint area should match the device side pad size area
> > (i.e., UBM). The UBM diameter will be smaller than the 0.2mm ball
> diameter
> > (you may need to ask the device supplier for this info since it's not
> > usually provided on the datasheet).
> >
> > * Use solder mask defined pads because: (1) a Cu-defined PCB pad <0.2mm
> is
> > not possible by most PCB fabricators if there are uvias in the pads; (2)
> > solder area of the PCB pads should be of consistent size; this is not
> > possible with Cu-defined pads due to exit traces, which draw solder away
> > and distort the shape of solder joints inconsistently. Solder mask
> defined
> > also allows for larger Cu pad, for which the PCB fabricator will thank
> you.
> >
> > * Is corner staking an option? In the absence of full underfill, your
> best
> > bet to pass drop test may be to apply epoxy dots or lines on the corners.
> >
> > Good luck!
> > Todd
> >
> >
> > -------------------------------------------------------
> > Todd MacFadden
> > Component Reliability Engineering
> > Bose Corporation
> > 1 New York Ave, MS 415
> > Framingham, MA 01701
> > 508.766.6259
> > -------------------------------------------------------
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Curt McNamara
> > Sent: Tuesday, April 19, 2016 6:56 PM
> > To: [log in to unmask]
> > Subject: [TN] .031 PCB and WLCSP
> >
> > I am reviewing a design with a .4 mm pitch, .2 mm ball WLCSP (9x9) on a 4
> > layer .031 FR4 pcb.
> >
> > These will be used like a remote control, so there will be force applied,
> > however there are supports for the PCB.
> >
> > Due to the presence of switches with cleaning restrictions, underfill is
> > not possible.
> >
> > Looking for any comments on potential reliability concerns. The design
> > could be changed to .064 if that would help.
> >
> > Thanks in advance!
> >
> >     Curt
> >
> >
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