Do you mean on the same board so as to have adequate solder for both packages? Here are some general guidelines for both devices

Board Design: 
	Ensure 0402 pad design is per IPC at the very least. I would recommend performing a DOE to determine and recommend to your customers, what pad design works best in your process. Minimize fillet length for 0402s to prevent tombstoning and component cracking. For BGAs, having board pads the same size as the BGA pads is recommended. Board surface finish should be planar (no HASL)

Printing:
	Stencil Design: stencil thickness (4-5 mils works optimally in my experience) and aperture shape should be investigated as part of the DOE. You MAY want to go with a step stencil if BGAs are present on the same board to ensure correct volume of solder for each device. good results have been obtained with a laser cut, electro polished stencil for 0402s

I would recommend having solder paste inspection capability (2D in the printer + height or 3D inspection) for both these devices to ensure a clogged aperture is caught as soon as it occurs. Reworking tombstoned 0402s is no fun.

Talk to you stencil printer manufacturer on machine specific guidelines.

Placement:
	Ensure that your placement machine is calibrated. Perform 0402 placements on a test board to measure process capability values (all placement machines should be able to do that as a routine part of calibration). Correctly program component heights for caps and resistors 

Reflow:
	Air reflow works optimally for both these devices. N2 reflow may increase chances of tombstoning for 0402s

Wash and handling:
	Protect the boards during wash process to prevent 0402s from being damaged by the wash conveyor. Operators should be trained to handle assemblies carefully (not slide them on the table during inspection, for example). Use of ESD foam backed trays to transport all assemblies with 0402s and BGAs should be instituted

Rework:
	In the rare instance that a rework of 0402s is requires, there are various tools available to make the job a little easier. Investigate and possible purchase some just in case. BGA rework requires dedicated hot gas rework equipment as you know.

This list is by no means exhaustive. I am sure you will get numerous valuable suggestions from other technet members as well. This should be a good start though.

Regards,
 
Amol Kane | Process Engineer
Catalyst Manufacturing Services, Inc.
941 Route 38, Owego NY 13827
Phone: (607) 687-7669 Extn 349 | Website: www.catalystems.com

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of prashant chopra
Sent: Tuesday, February 08, 2011 5:42 AM
To: [log in to unmask]
Subject: [TN] 0402 and BGA

Hi,
 
I need help to have some expert opinion, inputs, presentation or plans for implementation of the usage of 0402 and BGA in our manufacturing process.
 
What would be the critical requirements and readinees required for setting up a manufacturing line for the usage of the 0402 and BGA packages?
 
Thanks in advance for all the help and your time.
 
Rgds
Prashant


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