PCB Layout Related Questions(EMI/EMC Layout concepts) / High speed PCB design

[scriptx007]

Hi all

This thread i have created or questions i hav mind related to PCB design. they might sound silly but i request u to pls share ur ans.

first question. for 4 layer design stackup followed is SIG GND PWR SIG. this is the std stkup. what are the advantages of following such stack up?

second question: what procedure does pcb designer follows to determine thermal pad ground. ? as per based on parameters frm the datasheet of the device? if yes how?

i will keep on posting questions regarding PCB layout. pls share your ans.

 

[D.A.(Tony)Stewart]

1) depends on frequency and inductance of PTH's from layer 1 to 4. but this gives a microstrip ground plane for all controlled impedance tracks and good shielding and also possible low ESR dielectric between Vcc and Gnd.

2) Yes follow Mfg recommendations or IPC design handbook. and derate if internal ambient rises from other sources.

 

[scriptx007]

Thanx for the reply sunnyshyguy.
ok here is the simple example. LM317 regulator is used for voltage regulation. i/p voltage to it is 36 V & it's current is 0.5A-1A max. output voltage is 5V. so my question is how to determine thermal pad ground area. pkg is D2PAK.

for first question. what are the advantages if stkup is giving microstrip ground plane. can u pls share & if u dnt mind a simplified ans for this.

 

[marce]

Some links, also search this forum, all your questions will have been answered.:smile:

 

[FvM]

ok here is the simple example. LM317 regulator is used for voltage regulation. i/p voltage to it is 36 V & it's current is 0.5A-1A max. output voltage is 5V. so my question is how to determine thermal pad ground area. pkg is D2PAK.

Simple answer: For the maximum power dissipation of > 30W according to your example even an infinite copper pour won't work.

 

[marce]

Its only standard for 4 layer boards, a large number of boards these days are far more than 4 layers, then you add HDI PCB design to the equation and stack ups become infinitely variable.
PCB thermal management is also becoming more complex, my favourite tool for post design assessment is a thermal camera. Work out the basic requirements as best as possible using on line calculators, software if you have it and peer advice, but examining the finished product working at its full temp range using a thermal camera gives you invaluable feedback. Often parts that were not thought of as problematic can be the hottest. Of course you can also use Comsol multiphysics or similar, but for standard product the time and effort is not justifiable.

 

[scriptx007]

Hi FvM,

How did u calculated >30W? P=VxI ?

 

[tpetar]

Pd = (Vin - Vout) x current

 

[D.A.(Tony)Stewart]

To avoid thermal problem design must change to reduce input voltage to <10V or use Buck regulator instead of Linear. Many solutions on web.

 

[scriptx007]

Here is my next question guys..

Whats os ground bouns in layout point of view. in simple words. how it may crash your design?

 

[Rame]

Hey,Again it is like your previous question,the time you take to post your query here instead bit of research in this forum and bit of googling you had answers in tons to your query.

Just check this link https://www.edaboard.com/threads/88988/ hope it is helpful.

Regards,
Rame