EPC devices assembly support

Designing with GaN FETs and ICs
1

Hello,

I’m trying to solder devices (EPC2021) on the pcb with a stencil and solder paste, but I am having trouble not getting the paste to bridge. Right now, I can assemble it using the solder bumps included and some flux in a reflow oven, but i’d prefer using paste so I can visually inspect correct joins.

The problem can be seen in this photo:

WIN_20230310_15_34_33_Pro
WIN_20230310_15_34_33_Pro1920×1080 277 KB

The stencil used is 0.1mm thick and electropolished, and the paste used is chipquik NC191LTA35 (Sn42/Bi57/Ag1, type 4). Would the recommended course of action be to order a thinner stencil (ie 0.05mm), or is there a more viscous solder paste you would recommend me using to avoid this problem?

2

Hi,
I’m sorry to hear of your troubles.
Have you been using our recommend land patterns (solder mask defined) and stencil from the datasheet?
By the way, the Altium footprints for all our devices can also be found here: https://epc-co.com/epc/documents/altium-files/EPC%20Altium%20Library.zip

3

Hello,

Thank you for taking the time to reply. I have followed the EPC provided advice (I used the provided footprints as well), and i had this trouble.

I think my problem is the stencil printer I’m using is quite basic, and I’ll need to create some spacers to flatten the stencil to the PCB better.

Apart from this, may I ask if there are particular fluxes that EPC recommends for rework?

Kind regards,
Greg

4

Hi Greg,
I agree with your assessment, uniform solder deposition is very important, and care must be taken when dealing with small opening stencils.
For rework recommendations, please see quick-reference-die-removal.pdf (epc-co.com) and How2AppNote003 Assembly.pdf (epc-co.com)