All Leadless

It wasn't too terribly long ago that just about any design could still be built all thru-hole. Okay, maybe it was a little longer ago than that. Once the big CPU chips stopped showing up in PGA (pin grid array), thru-hole PC motherboard possibilities went out. Then when blue-tooth and Zig-bee came around, most if not all of those chips came out in BGA, LGA or QFN forms - no thru-hole. Anyway, it's not too difficult to do pretty much any design in all SMT now, but what about all leadless?

Okay, we don't really consider passives to be leadless, but they kind of are. So, we have all of our passives in a leadless like form. Now all we have to worry about are the chips.

I'll start with a Microchip PIC18F4550 in a QFN44 package. It's got built-in USB, so I don't have to worry about a separate USB chip. I'll load up a bootloader and it will all be happy. Wireless will have to wait for version 2.0. This is going to control a two side-by-side wheel platform scooter type thing, so I'll need a gyro and accelerometer. Digi-Key just sent out their "techzone" mini-catalog/magazine featuring just some of these type parts. I'll take the Analog Devices ADXL345 three-axis accelerometer in LGA form-factor.

I only need to worry about pitch and yaw, so a dual axis gyro should be fine. I'll try out the ST Micro LPY550AL in a 5x5mm QFN package. For voltage regulation in the prototype, I'll use a Linear Technology LTC3642 in a 3x3mm DFN package. It has a 3.3 volt output and can accept 5 to 45 volts in. That gives me the flexibility of powering off of a dedicated battery pack or off the scooter main battery.

All LGA or QFN/DFN. The only problem is soldering up the prototypes and next half-dozen or so units, for all of my friends, after that. I'm not going to stick those things in a toaster, and I certainly can't hand solder them like I could with the old thru-hole or TSSOP and SOIC chips. Oh. Wait. I work for a company that does that.

Duane Benson
Fight Uni!

Comments

[Kasamiko]

Do you have a 6x8 Eagle package for this chip?

[Duane Benson]

Hi David;

Your very question is one we've been trying to answer for a while. The way most other companies reduce costs is either by building higher volumes (which won't help you) or by making quality the result of luck rather than process.

We have a lot of systems in place to ensure consistent high quality with very complex jobs. Those systems and processes do make small jobs more expensive. That's perfect for commercial projects but I do understand that it does frequently take us out of the running for self-funded hobby projects.

[David R]

Unfortunately, last I checked, I couldn't get in the door for <$3-400 for even one QFN. Is there any way to make that sort of tiny run feasible for a hobbyist and for you?

[Jeff]

You would be amazed what a skilled tech (or hands-on design engineer) can do with a hotplate, a bottle of flux, a scope and a good touchup iron.

QFN - no big deal.
LGA - same thing, sometimes ground pads are tricky.
BGA - this is where I hand the board over to the professionals!