Based on my understanding, leveling using perform is standard (minimize the voiding as well). If design properly, there are solder joints can pull the parts in to position with a stop over built in on PWB (IBM late 80s publication if you can find them). The alignment for MM is not bad. Ball lens help. As for optical sensor, assume it is not as critical as fiber optics, with internal calibration build in the sensor (such as look up table for correction), shouldn't be hard. Of course, depend upon the design and application requirements.
Joyce Koo
Materials Researcher - Materials Interconnect Lab
Research In Motion Limited
Office: (519) 888-7465 79945
Mobile: (226) 220-4760
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Tuesday, July 03, 2012 12:39 PM
To: [log in to unmask]
Subject: Re: [TN] Coplanarity of Sensors
I know of no standard for something like this, but would think what is
acceptable deviation is negotiation on what your customer needs for correct
functioning of the product - and what you can actually do for the price he
will pay.
As you have probably found out already, a couple (at least) of the solder
companies do special preforms for controlling stand off height. These have a
non melting core and can be P&P from tape to the corners of the BGA.
Curiosity Question: I understand the need to reduce process variation, but
ultimately wouldn't the alignment have to be with respect to any optics
rather than to the PCB which by implication would need to be perfectly flat
- no bow or twist - and then itself (adjustably?) mounted to give the
alignment required.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Tuesday, July 03, 2012 12:39 PM
To: [log in to unmask]
Subject: Re: [TN] Coplanarity of Sensors
I do know that BGAs are not level.
I have seen a demo of a machine, A3DI, which accurately measures the height
of components, amongst other things, and it was interesting to see that all
BGAs had a slight tilt on them.
At the demo I could not find out how the tilt was related to the direction
of passage through reflow, however it was my guess that the two are related.
If you want more info contact Dave Hall <[log in to unmask]>
Regards
Rex
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of William Noel
Sent: 03 July 2012 12:20
To: [log in to unmask]
Subject: [TN] Coplanarity of Sensors
Hello - We are mounting light sensors on a circuit board and these sensors
come in a variety of packages (BGA's, QFN's etc) I was trying to determine
if there is a standard or spec that addresses the deviation from a "perfect"
90 degree angle of light addressing the sensor's active surface. Ideally
the sensor would be mounted such that direct light addressing the sensor
would be at a 90 degree angle to the pcb and subsequently to the sensor
itself. Anyone have any experience or advice? Thanks in advance.
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