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MLP (Micro Leadframe Package)



MLP (Micro Leadframe Package) | 1 April, 2003

Hi: I'm looking for input from anyone who has experience assembling the MLP package on PCBs. We are experiencing solder opens after assembly, and I'm curious to see how others are processing these critters.

The part we are using is a Semtech SH3000 (microbuddy) It is 3mm by 3mm square with four solder contacts on each bottom side. Since there is no leads on this package, there is no standoff from the PCB. Because there is no standoff/gap under part, we do not run it down our SMT assembly lines which use water soluble solder pastes. Our customer does not want to use a no-clean assembly process for the whole PCB. I do not think that a water wash system would reliably clean the organic acids from the water soluable paste under the part. The solder connections are on the underside of the part only, and are not visable after processing. I am having difficulty X-raying the joints to verify them.

Our assembly process for this part is as follows:

1. Screen print solder paste on PCB(water soluble flux type) 2. Place SMT parts (except Microbuddy) 3. Reflow assembled PCB (convection reflow) 4. Clean PCBs in water wash system 5. Flux Microbuddy location with Kester TSF-6522(no-clean "tacky" type flux) 6. Hand place Microbuddy 7. Local reflow of solder using handheld hot air tool. (Haako 850)

My questions are: A. What assembly processes are others using to attach this part. B. What inspection methods are others using to verify solder connections? C. Are others using water soluble solder paste, and then water washing?

Thanks in advance for any info you can share.

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MLP (Micro Leadframe Package) | 1 April, 2003

You're correct. There is no way you can aquous clean under a low stand-off part like a LGA.

Your approach seems reasonable, given your constraints. [As long as your customer is paying, what the hey!!! Give 'em what they want.]

Consider joining the 20th Century by changing to low residue fluxes.

So, what's causing your opens? Do you have: * Enough solder in your bumps? * A planarity issue with the solder bumping you're doing? * A LGA reflow profile that's warping the device? * A LGA reflow profile that's providing for full wetting of the LGA pads?

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MLP (Micro Leadframe Package) | 1 April, 2003

Try checking into ssd No clean process for the whole board. Contamination from paste is removed before you get the boards.

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