Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

EMI Shield

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EMI Shield | 8 August, 2013

I have a new product to build and it uses a SMD EMI board shield. I have never done this before. There are multiple components under the shield, do I place the components and then the shield and then reflow? Or do I have to reflow the components, reflow and then somehow do the shield?

The shield is a Laird BMI-S-103. I am concerned that if I try and do this with one reflow operation that the parts will not reflow.....

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EMI Shield | 8 August, 2013

Depending on the shield, the PCB, and the parts under the shield, we usually place all the parts, then the shield and reflow them all.

The shields usually have breakaways on the top so you can still inspect the components under the shield.

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EMI Shield | 8 August, 2013


Wow. This is a tough one. The part is a 1 pc where I'm used to seeing a 2pc. In our case, we have several assemblies using a 2 pc system (see Laird BMI-S-207-C and BMI-S-207-F). The "C" and the "F" stand for Cover and Fence. The Fence is placed as part of a normal SMT process and reflowed with the rest of the parts. The Cover then snaps over the Fence after parts have been inspected, XRAY'd, touched up, etc.

A 1 pc system, like yours, will eliminate the possibility of inspecting what is under the cover if it's installed along with the rest of the SMT parts. Kinda scary.

Push back on your customer to specify a 2pc system that reduces everyone's risk. If any of our customer's specified this part, it would be a no bid unless there was agreement to change the BOM.

My 2.

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EMI Shield | 8 August, 2013

Placing and re-flowing the shield is of course the most economical. But once the shield is placed and reflowed this all but rules out inspection test and rework. Reflow should not be an issue if you have a decent forced air convection oven. You may want to validate your process by masking or taping off the shield pads, placing the shield on the board and reflow. You can then remove the shield and verify reflow. Once your reflow is verified it would be wise to add in process inspection step to verify all components under the shield are placed properly before shield placement. If rework is required it will be complicated, in most cases requiring a hot air rework station. Shields have a tendency to warp and or twist during reflow so flushness to the board could be an issue also. Of course a two piece shield with a snap on cover would be very nice. If run quantities are low it may be well worth it to just hand solder in second ops after inspection and test. Good Luck

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