I agree with Ben - the desire to not have open vias or dimples in BGA pads
is to avoid having void formation but per the IPC-JSTD-001 specification,
voids are not necessarily defects unless they exceed 25% of the Xray image
area. As Ben detailed, adding an unnecessary board fabrication requirement
comes with a cost.

Dave Hillman
Rockwell Collins
[log in to unmask]


On Wed, May 28, 2014 at 3:20 PM, Gumpert, Ben <[log in to unmask]> wrote:

> I assume that the concern is for voids in the solder joint, which the
> dimples tend to cause. Which indicates that printing solder paste does not
> fill the dimple. I would expect that solder jetting to better fill a dimple
> since it flows better, but I don't have any experience with it.
>
> But voids are not necessarily a defect, especially when design induced
> (see J-STD-001 Table 7-14 Note 1) so I would be hesitant to add a
> requirement to your vendor (and likely cost to your product) without
> understanding why the assembler is asking for this.
>
> Ben
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
> Sent: Tuesday, May 27, 2014 7:43 AM
> To: [log in to unmask]
> Subject: EXTERNAL: Re: [TN] Dimples - Bumps - SolderJetting
>
> Interesting, printing would fill the dimple. I had not considered that
> problem. Dispensing would be an issue too.
> Those are pretty significant tolerances. Maybe the committee that writes
> that standard should revisit. Looks like  you are going to need a note on
> your drawing. For most BGAs the majority of solder comes from the Ball, but
> you must have enough paste to get good contact with the ball. How deep is
> your deposit?
>
> Guy
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Roland Jaquet
> Sent: Friday, May 23, 2014 11:48 AM
> To: [log in to unmask]
> Subject: [TN] Dimples - Bumps - SolderJetting
>
> Dear Technetters,
>
>
>
> We have an issue with BGA and vias in pad and the usual flatness required
> for assembly and Solderjetting.
>
> The IPC-6012C for Class 3, says it is acceptable for Dimples up to 75µm
> and bumps up to 50µm .
>
>
>
> At the assembly line, they do not want Bumps and almost no Dimples (max
> 25µm)
>
>
>
> Do we have any Pro/Con experiences as to where to lead and define
> boundaries for it?
>
> Is there some more specs in regard of SolderJetting ?
>
>
>
> Thank you for your help
>
>
>
> Best Regards
>
> Roland
>
>
>
>
>
>
>
>
>
>
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