I keep hearing this expression thrown around when talking about or to PCB fab houses. Can someone tell me what it means, or refer to ?
Electronic – What does the term “turnkey” means or refer to in the Engineering/Manufacturing environment
pcb
Related Solutions
A coil energized with current can create a force of attraction to an iron object. It can also repel a magnet if the polarity is correct. That force is: -
Force = \$\dfrac{(amps\cdot turns)^2\cdot \mu_0\cdot A}{2\cdot g^2}\$
Where
- A is cross sectional area of the electromagnet
- g is gap to your magnet
- \$\mu_0\$ is 4\$\pi\$ x \$10^{-7}\$
Let's say the force needed is 0.2 newtons. Your required coil is 20mm in diameter and lets assume that all the turns are closely packed around a diameter of 20mm. The gap to the magnet is 10mm. Lets say you can get 100 turns wound at this diameter...
Re-writing: -
Amps = \$\sqrt{\dfrac{20 \cdot 2 \cdot 0.01^2}{100^2\cdot 4\pi \times 10^{-7}\cdot 3.14\times 10^{-4}}} \$
That's about 32 amps.
But, it's going to be a lot worse for a spiral design because as the coil diameter gets tighter (for the inner turns), the effective area of the electromagnet gets smaller.
I think you might be looking at something like 100 amps for a 100 turn coil and basically it looks unfeasible. Of course, if your force is significantly less than 0.2 newtons then the amperage would drop so plug your own numbers in to the formula.
Once you have got an idea how much current is needed then that is the time to work out how to drive your electromagnet.
TI recommends using solder-mask-defined thermal pads without solder mask around the thermal vias. Solder going though the holes and causing voids (not shorts) is said to not be a problem if the via hole diameter is kept to 0.3mm or less. Spacing of 1mm is suggested, and of course the vias should not have thermal reliefs.
Putting vias just in the corners would degrade the thermal performance.
If cost is no object, some fabs can plug the thermal via holes with copper.
If the pad is actually used to carry significant current then the usual considerations apply, you can split the plane or do other things to control current flow, but it is not usually necessary, especially on a mostly digital board. You really can consider all the thermal vias a single connection to the ground plane for most practical purposes- an exception might be if you had some insanely sensitive amplifier very close to the thermal pad so that it caused voltage gradients in the ground plane- but that would be bad layout practice to have such things too close to each other and without some kind of isolation moat etc.
Related Topic
- Electronic – Are core and prepreg dielectrics interchangeable
- Electronic – What impact, if any, does the solder mask color have on the electrical and mechanical properties of a PCB
- Electronic – What does Minimum Slot Aperature mean
- Electronic – How to change the dimensions of a PCB in Altium Designer 19.1 using by entering the value I want the dimension to be
- Electronic – the purpose of the PCB jumpers in the attached image
- Electronic – the best approach to test a new PCBA
Best Answer
"Turnkey" means that you only provide documentation to someone else to build something. They then source all the parts, get other parts modified or made, etc. Basically you send them specs and money and they send you fully built units.
Note that this doesn't really apply to PCB fabrication. Or more accurately, PCB fabrication is basically always turnkey anyway, so that term is not used in that context. You don't provide copper sulfate, laminated FR4, or etching solution to the PCB house. You provide only Gerber files (the documentation), and they do and buy whatever is necessary to make the complete finished boards.
What you are probably confused by is that some PCB houses also offer assembly services. Those could be turnkey or not. But that's really a assembly issue. Someone doing turnkey assembly for you would get boards fabricated as part of the process. The the same company is offering the turnkey assembly service that is also a PCB house, then they will produce the bare boards internally. However, there are plenty of assembly houses that aren't also PCB fabs. In that case for a turnkey job, they will subcontract out the PCB fab, usually to a company they have special business relationship with just for that purpose.