I'm at the point where I need to select bypass capacitors for my design. And I'm planning to make a lot of these boards, so I'm trying to keep the assembly and parts cost down. I'd also prefer to use smaller package sizes.
The problem with Tantalum caps is besides their using larger package sizes than the ceramic caps, they're also more expensive, and if I have to use two capacitor types then I have to pay the $7 reeling fee for both and it seems like a waste to spend $40 on tantalum caps if I already had to purchase 10,000 ceramic caps of the same size.
Here's some examples of the prices I've calculated for different capacitors in various quantities:
$40 for 50 47uf capacitors? EMK325BJ476MM-T $21 (10K) 587-1227-2-ND .1uf 10V 0402 $27 (10K) 587-1451-2-ND .1uf 16V 0402 $16 (4K) 0603YC104KAT2A .1uf 16V 10% 0603 $20 (150) C2012Y5V1A106Z 10uf 10V 0805 or $50 (2K) $75 (50) C3216X5R1A107M 100uf 10V 20% 1206 or $116 (100)
$46 (250) CAP TANT 10UF 10V 20% 1206 - F931A106MAA (May be unsuitable for voltage regulator... One needs to be both on input and output and input > 10V) $80 (500) CAP TANT 10UF 16V 20% 2312 - TAJC106M016RNJ or $73 (250) (Not worth it!) $55 (250) CAP TANT 10UF 16V 20% 1206 - T491A106M016AT
$31-$41 (100) Avg price for 10uf 16v in 1206 package
I've already changed the voltage regulator I was planning to use as a result of the prices I was getting for caps. I was going to use this one: http://www.diodes.com/datasheets/AP1084.pdf
Which was the cheapest 3-5A regulator I could find, but it requires two 100uF capacitors and those are really expensive in an SMD package and probably even moreso in electrolytic. (Well, they're expensive when you're trying to get 50 boards made on the cheap, and you'd need 100 of them.)
But it will cost $38 more for 50 TI regs, and $57 more for 50 Micrel regs. So it almost makes it a wash between using the cheaper regulator with the expensive 100uF ceramic caps, or the more expensive regs that require the less expensive but still costly tantalum caps.
It might not seem worthwhile to worry about saving $40 on 50 PCBs but the cost of these boards is adding up fast, so I'd like to reduce costs where I can.
Oh, and another reason I'd like to avoid using the tantalums is I've heard they can catch fire with overvoltage and these boards will be used by people whom I don't trust not to do crazy stuff with them. Also they're polarized and I'm not sure how to specify on the PCB layout which way they go for the assembler.