balancing PCB assembly and component costs for low volumes

[djacobow]

I designed a fancy holiday ornament for my friends and family last fall. It was a big hit, and a bunch of people suggested that if I had some for sale, they knew people who would buy them.

I did not have any for sale. I hand-assembled the 50 or so that I gave away, in part because the two PCBA quotes I had were too high for my tastes for such a simple device. This was a "product" with a BOM < $6: basically an attiny, some 595 shift registers, and a bunch of 0805 LEDs and associated current limiting resistors, an AAA battery holder (only TH part), a few 0805 caps, and some buttons. The quotes included about $10-15 in assembly cost each, for qty 100.

I *think* but am not certain, that the PCBA quotes were high because of the number of individual components. If so, then replacing the 595+resistors with an LED driver could be more cost-effective, even though the LED driver part would be on the order of $1 while the 595's are < $0.20, and the resistors are basically free. But the quotes were not detailed enough for me to know for sure what was driving the price.

Is there a PCBA house that has a detailed on-line description of how they price?

Best,
Dave J

[soubitos]

I am the last who could answer this but in my quest to locate a PCBA service suitable for my designs i always come into the confusion if they need to know how many paRts are on the pcb or how many paDs... Then my next question not really answered is ie for a pcb with 10 parts with 30 pads... say 2x4cm .. palenised to fit 20 in one panel do they count individual parts/pads or what-else? Therefore, and as long as my needs can be handled by "in house assembly" i stopped searching! LOL

[floobydust]

I find PCB assembly houses keep their pricing to themselves. It's very competitive.
Most will discuss the high-cost steps on a board build, but others simply like the extra money and play dumb.
If a PCBA house has many assemblers, then they don't mind awkward builds. The "PnP robot only" places charge a fortune for anything beyond their machine's abilities.
Smaller PCB assembly houses have better pricing on low volume builds.

Components on both sides of the PCB usually doubles PCB stuffing costs.
For SMT parts, it's a fixed cost per part placed, pennies per part. But limited to the number of reels they can support, for one load.
Any through-hole, hand placed parts, manual wiring- adds the most cost. Paste-in-pin can overcome the TH parts extra step.
Getting firmware in the MCU is another high cost operation because it's manual labour connecting things. Final PCB test is another high cost step.


I would see if you can go 100% SMT and talk to a few PCBA places and see what are the cost drivers in the design.
Panelizing the PCB's better to suit their line can lower the costs too.

[djacobow]

Components on both sides of the PCB usually doubles PCB stuffing costs.

All the components were on one side of the board, except for the battery holder, the only TH component. However, I got a quote without the battery holder in the BOM (I'd do it myself) and it wasn't that different.

For SMT parts, it's a fixed cost per part placed, pennies per part.

Is that true if the parts are the boards are being hand-assembled. My experience doing the first batch myself is that It is about equal effort to solder a 16 pin SOIC as it is a diode. Actually, the SOIC is easier, because it's easier to tell its orientation and to get it off the tape the same way every time.

Any through-hole, hand placed parts, manual wiring- adds the most cost. Paste-in-pin can overcome the TH parts extra step.
Getting firmware in the MCU is another high cost operation because it's manual labour connecting things. Final PCB test is another high cost step.

I think I will do the FW programming and test step myself. With a pogo adapter and a powered programmer, I can do this pretty quickly, and I feel like if I'm going to sell these, at least the first batch I'd like to see working with my own eyes. I've also heard of stories where people sent a hex file to an el cheapo board house, and knockoffs were for sale on eBay before the designer got his own boards!

Panelizing the PCB's better to suit their line can lower the costs too.

Does panelization affect assembly costs, too? I let the board house panelize for me and I the boards were really quite cheap. I think about $1.50 each. It was the assembly at 7-10x that that sucked.

[stmdude]

I'd upload the design to MacroFabs online system and play around with it there.

It's been a while since I used it last, but as far as I remember, it allowed you to play around with the BOM and a lot of options to figure out where the money went.

[Ice-Tea]

The killer is ussualy setup cost (ie the time it takes to procure components, check files, program and load the machines, stencil cost,...) The placement itself is, as others mentioned, a few cents max per component. That will set you back 500$+ or so. Now spread that over 100 boards you want to get stuffed and...