what are DFM considerations for SMD Component placement on both side of PCB

Question

I am designing tiny flight controller for smartphone controlled plane and drone... rev-0 of the same is approx 5cm x 5cm and all components on top as per pic below..

now I am trying to reduce size and weight of flight controller board by using WiFi SoC chip rather than module and placing components on both side of board ...

Please suggest considerations for placing components on both side of PCB board so it can be made by machine (Automatic placement and reflow machine)

Key Parts:

ESP32-PICO-D4 chip QFN

CP2102 USB-UART chip QFN

MPU6050 ACC-GYRO QFN

Misc-SMD LEDs, Resistors, Diodes, Caps, LDOs, BJTs, MOSFETs

Thanks,

Ravi

michaelkellett · Answer

Hey Clem, that's a bit out of date ! I think Ravi will be into 0402 and a PLCC would be bigger than his drone (well, not quite). It's much more common with fine pitch work to use solder paste and reflow on both sides of the board. MK

geralds · Answer

If I now take your picture as an approach (as I see it's a 2-sided board), I suggest you can place all the resistors and capacitors, transistors on the bottom side.

The ICs, the module and the connectors can be placed on the top side.

Then the board gets smaller and if you also pay attention to the mounting holes, I see no problems with the assembly of the board.

You can mill out the board with fingers for the mounting holes, so that it can be directly mounted on the drone.

Or you can assemble with fasteners, e.g. large screws, or mounting brackets to the board.

Assembly cost I think will be marginal, plus-minus...

Best Regards

Gerald

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michaelkellett · Answer

Placement on both sides will cost more - if you put only small parts on one side not too much more, if you put heavy parts on both sides then costs will rocket because they will need to be glued. The rule is - talk to the assembly engineer before you commit yourself. How many will you make - if its just a few it doesn't matter. Be very careful about putting any parts under the RF chips/modules - there will be rules in the data sheet. Are you sure you can design an RF module better (smaller, lighter) than people who make millions of them - do you have the RF test gear etc. You might do better to stick with the module (get the lightest one you can) and minimise the size and weight of all the other stuff. MK

geralds · Answer

For example, if you place a resistor (or other warming components) underneath the RF module on the bottom, this resistor can heat the module up. That's what you have to see too. Or RF parameters could change because such components cause EMC problems. Sticking the components on the bottom is relatively, nominally correct. There are solders that can hold the component well. But, it works only on small components.

ravi_butani · Answer

Agree... Have a look at very initial proto of same drone... which already given enough Adrenalin rush.. DIY tiny Smartphone controlled drone DIY Smartphone controlled drone with Altitude hold Thanks...