Re: MCM footprint?

[André van der Meer <andre@xxxxxxxxxxxx>]

My design for a 6-layer Axis protoboard uses 0.6 mm pads +0.1 mask.
We had just the MCM fitted by an external  company (3 boards)
I gave 'm this reflow profile
http://developer.axis.com/doc/hw/mcm4_16/22545%20Reflow%20Profile.pdf
but I think they used a bga repair/rework station.
All boards work great.

Greetings André.
----- Original Message ----- 
From: "Sam Silverstein" <silver@xxxxxxx.se>
To: <dev-etrax@xxxxxxx.com>
Sent: Wednesday, March 29, 2006 2:05 PM
Subject: MCM footprint?


> Is there any documentation on recommended PCB design for the Etrax MCM 
> beyond the
> comment "Common design rules should be applied"?
>
> We have been having problems soldering our current prototype board, which 
> has 6 layers
> (3 signal, 2 power, 1 ground) and has 2 BGA components (the ETRAX MCM 4+16 
> plus
> a smaller Xilinx FPGA). When all of the solder balls are melted, they are 
> often unable to support the
> weight of the MCM, and a rather messy collapse occurs. If we shorten the 
> time of the reflow phase to avoid collapse, the large number of 
> non-connected (NC) pads leads to uneven results. We are now reconsidering 
> a redesign to make assembly more reliable.
>
> So here are my questions for other board designers:
>
> 1. What pad dimensions do you use (land size, solder mask)? The ones on 
> the MCM demonstrator board seems to have a diameter of 0.75mm (?) Our 
> current ones are a bit larger than that.
>
> 2. How do you deal with non-connected pads? Have they been an issue in 
> other designs?
>
> 3. We use solid ground and power planes under our MCM. Does this have any 
> thermal consequences?
>
> 4. Has anyone else developed a DRS22/24 reflow profile for the MCM, and 
> would be willing to share?
>
> Thanks,
> Sam
>
>
>