it is all depend upon what kind of stress - temp cycle most likely you have experience shear load, vib and impact are different, pending on direction (6 faces, x-edge, y corner, etc.). strain rate also place the role. voiding can not be a uniform acceptable criteria... it is all depend upon how much design margin allow. (we can see the cow go home...) jk > If the criterion was the evaluation of the ratio load/area, one should > sum only the void areas that lie on a same plane (perpendicular to the > load), > > For example, if the direction of the load is vertical, the areas of > voids placed on higher or lower planes shouldn't be summed, because the > solder joint area which bears the load in each plane depends on the > voids intersected by that plane, not on the voids placed higher or lower > in the solder joints. > > Since the sum is extended to the entire volume of the solder joint, the > criterion would seem another one. > > Enrico > > Il 08/05/2015 15.55, Ed Hare ha scritto: >> I would suggest that the area criterion is appropriate since stress = >> load/area. It is not a missing mas issue in my opinion, it is a >> reduction in load bearing area that is of concern. >> >> Ed Hare >> VP SEM Lab, Inc. >> www.semlab.com <http://www.semlab.com> >> >> On Fri, May 8, 2015 at 5:15 AM, Enrico Galbiati >> <[log in to unmask] <mailto:[log in to unmask]>> >> wrote: >> >> I would like to ask anyone if there are any reliability data >> regarding the evaluation of voiding in a solder ball (BGA). >> >> In both the standards IPC-7095C and IPC-A-610F, the voiding in the >> solder balls is evaluated measuring the area of the voids. >> However, the weakening of balls caused by voiding should depend on >> the amount of the missing material caused by the presence of >> voids. If this is true, the amount of the missing material should >> be measured by the total *volume* of voids, not by the area. >> Consequently, the limit should be set on the volume, instead of >> the area. >> >> For example, with the present rule based on the percentage of area >> of the voids, a solder ball of 0,85 mm diameter, with a single >> void of 0,45 mm diameter, is acceptable, since the percentage of >> voiding is 28%, thus less than the maximum limit of 30% (ref. >> IPC-A-610F). In this case, the missing volume of the material is >> 15%. >> >> Considering another example, if a solder ball has 6 voids of a >> 0,20 mm diameter each, giving 33% of the area of voiding, would be >> rejected. However, in this last case the percentage of the missing >> volume is only 8%, i.e. less than the previous case (about 53% of >> the previous case!). >> >> So, the ball of the second case is rejected, even if it stronger >> that the one of the first case. On the contrary, it is the solder >> ball of the first case that should be rejected. >> >> Enrico >> >> -- >> Enrico Galbiati >> Consulenza Affidabilità e Normative >> Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy >> Desk: +39.039.8908.4547 <tel:%2B39.039.8908.4547> - Fax: >> +39.039.8908.5051 <tel:%2B39.039.8908.5051> - Mobile: +39.335 >> 6833616 <tel:%2B39.335%206833616> >> E-Mail:[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] <mailto:[log in to unmask]> >> ______________________________________________________________________ >> >> >> >> >> -- >> Ed Hare >> gmail - [log in to unmask] <mailto:[log in to unmask]> >> gvoice - 360-453-7550 > > -- > Enrico Galbiati > Consulenza Affidabilità e Normative > Via Kennedy Ingresso 2, 20871 Vimercate (MB) - Italy > Desk: +39.039.8908.4547 - Fax: +39.039.8908.5051 - Mobile: +39.335 6833616 > E-Mail:[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] ______________________________________________________________________