Do you think tipping film caps in the reflow oven could be due to uneven or too much solder? The film caps tend to be buoyant in the solder pool?
That particular example probably tombstoned because the oven heated the board and part unevenly. The footprint probably isn't helping, either.
I've seen designs with 0201 components half on a solid ground plane and there is no tombstoning, but that's with a professional reflow oven. It can be tricky.
I've seen designs with 0201 components half on a solid ground plane and there is no tombstoning, but that's with a professional reflow oven. It can be tricky.
Last edited:
Stencil was used and the paste was evenly applied. This was the second time it occurred!
Member
Joined 2009
Paid Member
probably limited by physics - those multilayer caps have stresses from materials mismatch etc. maybe they are too fragile when too large and competing technologies become more attractive at larger values in terms of price/performance.
NPO/C0G are so good because they use thicker dielectric. That makes them (much) larger, physically.
The reason that X5R etc is so bad is because the dielectric is so thin that you get effects or mechanical deformation with high field strength and voltage coefficient. That makes them so small physically ;-)
All plain physics.
Jan
The reason that X5R etc is so bad is because the dielectric is so thin that you get effects or mechanical deformation with high field strength and voltage coefficient. That makes them so small physically ;-)
All plain physics.
Jan
You can get a 1uF C0G for $8 if you want one badly enough...
WIMA and Kemet SMT PPS caps max out at 2.2uF.
And Rubycon MU acrylics go up to 22uF!
Last edited:
It is physics. The dielectric constant of MLCC dieelectrica is several orders higher enabling big capacitance value with tiny caps
Indeed, specifically the high value MLCC capacitors use ferroelectric dielectrics like barium titanate and its relatives, where the lattice geometry changes as the charge builds up - this makes them microphonic, non-linear and highly temperature sensitive.
These materials can have dielectric constants 100's to 1000's of times more than normal materials - hence large capacitance in small volume.
Barium titanate - Wikipedia
As I suspected, so its bumping up against a physical barrier that cannot be miniaturized by a more modern process.
Many thanks for fleshing out the detail everyone! For the most part I try to design so I dont need high value filter caps (signal) anyway, but occasionally I wish for a c0g that is 10-100nf at 0603
Many thanks for fleshing out the detail everyone! For the most part I try to design so I dont need high value filter caps (signal) anyway, but occasionally I wish for a c0g that is 10-100nf at 0603
