BGA Packages for hobbyist project

[joeyjoejoe]

I'm looking to design a battery charger with built in data-logging. The requirements were I2C, capable of charging to 4.35V, 1 cell, and being able to read the charge current and voltage via I2C for the data logging.

I've spent a few hours looking at TI's offerings, and found the following

BQ25871 - 42DSBGA

BQ25892 - 24WQFN


The second would work, but has only a 7-bit ADC. The first is my preference - it's very simple and meets my needs, and even better, has a 10-bit ADC built in for measuring charge current/voltage. However, it's in BGA form, and 0.4mm pitch at that. Even just a breakout board to do prototyping looks pricey.

Took a few hours to find these 2, filtering out other TI options.  I shudder to try and go through a handful of other manufacturers and do the same exercise.

Is working with this package size feasible and/or worth it?

[dmills]

0.4mm ball pitch?

Out of reach for the cheap hobbyist PCB  places, you will want filled and plated via in pad at least, if not microvia in pad.
If the ball count was lower you can sometimes do things by careful fanout, but 42 is a bit high to easily pull that off.

Time to go hunt down something a little more manageable unless you want to pay the likes of Wurth a few hundred for a prototype card.

Regards, Dan.

[joeyjoejoe]

Dang, that's what I figured but didn't want to accept

For the future, is any BGA manageable for hobbyists with the cheap fab houses? 0.6mm? 0.7mm?

[stmdude]

For the future, is any BGA manageable for hobbyists with the cheap fab houses? 0.6mm? 0.7mm?

I've done a few PCBs with 0.8mm BGAs. Enough to squeeze in two 3.5/3.5mil traces between the balls, so fanout doesn't require a zillion layers.

3.5/3.5mil traces is the smallest I've found for a reasonable (read: cheap) price.

[Mr. Scram]

I hate that cheap PCBs are now a reality and that manufacturers are moving towards BGAs and CSP that are one again out of reach for smaller players. Some chips don't come in anything else.

[DJohn]

I have no experience with 0.4mm ball pitch, so it might still be beyond the hobbyist level.  But the pinout does make a small effort to help you: each of the last four columns contains one function.  From the right, you get a whole column of VBUS, then one of PMID, then two of VOUT.

If you can get one track between two pads, you can get the second column out without vias.  That's all you need.  It's still a big 'if', and I don't have the experience to say whether it's possible or not.  0.4mm is not a lot.

[joeyjoejoe]

Yeah, I think it's enough of an unknown/hurdle that I don't want to spend cycles designing to realize I can't touch it. I can probably find a simpler i2c charger IC, and then add a current shunt and voltage sensing from the MCU directly and get at least 10bit resolution (AVR) or more (Teensy). It would have been nice to pull this all off with 1 chip but doesn't look like it will happen!

I guess my only question is do I need to stop charging to read the cell voltage? Do these IC's do that as well when they are all baked into one?