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 > > > > > > ______________________________________________________________________ > > This email has been scanned by the Symantec Email Security.cloud service. > > For more information please contact helpdesk at x2960 or > [log in to unmask] > > ______________________________________________________________________ > > > > ______________________________________________________________________ > > This email has been scanned by the Symantec Email Security.cloud service. > > For more information please contact helpdesk at x2960 or > [log in to unmask] > > ______________________________________________________________________ > > > > ______________________________________________________________________ > > This email has been scanned by the Symantec Email Security.cloud service. > > For more information please contact helpdesk at x2960 or > [log in to unmask] > > ______________________________________________________________________ > > > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please contact helpdesk at x2960 or [log in to unmask] > ______________________________________________________________________ > ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________