heat-protectionpcb-designthermal
I would like to make PCB board for TLE 5206-2G (check the datasheet).
It is TO263 package.
Basically, what i dont know is how to transfer heat out of the IC. I saw few PCB's that has little copper square with grid of holes in it. Is that what is used for taking out the heat?
Datasheet (page 21) says: Metal surface min. X=7.25, Y=6.9. Is that refers to heat transfer surface ? Will plated holes enhanced heat transfer ?
This is just general stuff, you should really try to put a bound on the expected acceleration forces, the period and duration of those forces, thermal conditions, and expected angles of impact to get the information you need to make the design robust.
What is the most force that would be OK on a board with no impact hardening measures taken? (Am I worrying too much about a non-issue?)
This is very difficult to put a single number on, it depends on the types of components used and the direction/frequency of the hits.
Are there any design practices that should be followed for the PCB?
Lots of attachments to something solid. One of the most likely failure modes is the PCB flexing which can cause the solder joints on the PCB to crack causing intermittent or complete failure of the connection. I would try to keep the PCB as compact as you can while providing as much attachment to something that won't flex (steel enclosure) as you can. The smaller the PCB the smaller the 'overall flex' of the board. Something like 4+ layer design with solder copper power and ground planes should also add to the rigidity of the PCB but can cause additional thermal flex. Depending on what your needs are, there are specialized PCB substrates that are more rigid than your stock off the shelf FR-4, such as substrates which employ carbon fiber composites vs fiberglass.
What are the weak points in a design that lead to mechanical failure?
Are there parts that should be avoided for a more robust design?
See the list above but keep all parts as lite and as close to the PCB as possible.
At what force levels should I start worrying about the safety of the parts themselves?
Again this is hard to put a number on. If the device is getting hit 'edge on' to the PCB than your concern is lateral shear forces. What force causes a problem there is dependent on the IC. A large heavy IC with few, small attachments to the PCB is probably the worse case. Maybe a tall pulse transformer or something like that. A lite weight, short IC, with many attachments is probably strongest. Something like a 64pin QFP, even better if it has a large center pad. Some useful reading on this topic: http://www.utacgroup.com/library/EPTC2005_B5.3_P0158_FBGA_Drop-Test.pdf
Some parts may be internally damaged by high G-forces, this would be on a part by part basis but would mostly be limited to devices with movable internal parts. MEMS devices, transformers, mag-jacks, etc, etc.
Comments
Have you considered using 2 boards? One small board with the accelerometer which is actually stiffly attached to the enclosure and a second board with the rest of the electronics on it which can then be mounted with a shock absorption system. The shock system could be as simple as rubber supports or as complex as the systems used in hard drives depending on needs.
Your going to need a pretty fast processor and a pretty fast, wide range accelerometer if you want to get accurate measurements of impact events such as getting hit with a hammer.
Just a fan blowing over the PCB won't be sufficient; a TO-263 doesn't have good thermal contact with the air surrounding it. I would solder this
heatsink over the FET. Like I said in another answer earlier today an SMD loses much more heat through conduction than through convection, but the heatsink has better convection loss thanks to its larger surface. The heatsink mounts over the SMD, not on it.
Heat transfer will occur via the PCB's copper, so increase the TO-263's pad so that the heatsink shares it.
Best Answer
These sorts of devices (surface mount with exposed metal) are meant to be directly coupled to heavy copper on the PCB to get the heat out of the device.
Usually this involves a multilayer PCB, with a bunch of vias that connect copper on several layers to the device metal. The vias not only channel heat through the PCB by conduction, they also ensure that the device is well soldered with good copper-to-copper contact.