It depends on how tight you want to pack the parts. With PTH, it is hard to justify 4+ layers, but with smt it is a different ball game.
low end audio, is so cost sensitive, hard to justify even two layers
and if know one has noticed the industry is going towards leadless packges, DFN/QFN
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The microwave substrates (grey color) I am familiar with are not laminates (other than the copper) . extremely stable mech and elect. for pcb use.
Basic info and related sources and articles found here: http://mwrf.com/materials/selecting-optimal-microwave-substrates
-RNM
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Oh I recall saying you are a half a$$ EE if you can't lay out your own pcbs
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discarding rest of the rant would you care to elucidate on this point. It could infer many things and I could think of many cases where and intelligent EE would chose to sub out the layout as it would optimise one or mother other variables, such as earning potential or ability to get some sleep that week
I don't know that Teflon is used much anymore I saw it 30 years ago at 1 GHz along with all its poor mechanical properties. These days Fr 4 series or equivalent is pretty darn good. Panasonic, Isola and Rogers all have a nice range of stuff available. Rogers 4350 is way overkill for audio but I specify it and it is really wonderful to work with. Only a small part of the cost compared to the metal work. Not having a sales/ marketing department it is marketing by tech boys I guess.
A bit more specifically, it is the glass transition temperature of the material. Sometimes referred to as the heat distortion temperature, the regime where it loses physical strength and the expansion coefficient transitions to a much higher value.
I would tend to disagree. Given that darn ROHS initiative and the switchover to lead free solders, higher Tg boards provide better sustainability through the soldering process. Lots of heartaches occurred when the old lower Tg boards were used with the higher temp solders. Through hole plating and vias were hit particularly hard.
Long components can also suffer, especially if they are surface mount, due to residual shear forces on the solder joints caused by differential TCE upon cooldown.
John
We called that, through it over the wall layout
esp. if it was a third party. In many cases it might not make a bit of difference. in complicated or high performance layouts it was very important to see through the layout process in finite detail.using a third party usually lengthened the pcb time frame because there were many back and forth reviews of complicated layouts.
And that is the bean counter telling me how to do my job
yes I understand exactly what you are saying and it is justified or forced upon a EE in a big company. i have experienced it, as i was one of the few EE's that did my own layouts for a time. i was promoted from layout to board design so I did have an advantage over the other EE's because they were not trained in pcb layout. some tools like allegro are complicated to learn and figure out.
A lot of the work is building libraries.
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I concur with John here, with lead free solders I would be looking at a Tg of preferably 170 deg C.
IPC-2221B tables 7.2 and 7.4 will give you material CTEs and calculated reliability figures for solder joints.
IPC-4010 series covers...
Key Environmental Material Properties.
Dielectric constant (Er or Dk)
Dielectric losses (Df)
Thermal expansion (CTE)
Glass transition temperature Tg
Moisture absorption (wt%)
Temperature at delamination (Td)
Glass weave.
Also listed are:
Flexural modulus
Tensile strength
Each materials specification sheet has more detail.
For the various flavours of FR4 there is a construction selection guide
covering the various parameters, allowing a basic choice for a particular design.
IPC-2221B tables 7.2 and 7.4 will give you material CTEs and calculated reliability figures for solder joints.
IPC-4010 series covers...
Key Environmental Material Properties.
Dielectric constant (Er or Dk)
Dielectric losses (Df)
Thermal expansion (CTE)
Glass transition temperature Tg
Moisture absorption (wt%)
Temperature at delamination (Td)
Glass weave.
Also listed are:
Flexural modulus
Tensile strength
Each materials specification sheet has more detail.
For the various flavours of FR4 there is a construction selection guide
covering the various parameters, allowing a basic choice for a particular design.
Has anyone looked at the properties of the glass and paper phenolic laminate materials as regards to electrical properties? I think the paper phenolic materials which would use flat sheets of paper would not have the problems associated with the glass woven cloths as far as the changing distance to the substrate? I think it still meets the FR4 rating, it may even exceed what the epoxy rating. What say you Sy, any reason that this type of material can't be used for electrical substrate? I don't think for audio there is any real reason to look beyond glass/epoxy laminate but perhaps in the Ghz range this is another solution.
Yup, the material Tg is chosen these days to handle the assembly extremes vs the actual circuit operation.
Think about it, if the parts are packaged using epoxy then why would anyone have an issue with the pcb using epoxy
Now if you are using hermetically sealed packages then you are in a different league.
Think about it, if the parts are packaged using epoxy then why would anyone have an issue with the pcb using epoxy
Now if you are using hermetically sealed packages then you are in a different league.
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here we go again on teflon pcbs
Oh I recall saying you are a half a$$ EE if you can't lay out your own pcbs
.
Load of rubbish, these days the best layouts are done by dedicated PCB designers, who study and understand all the aspects of PCB design, as well as the fabrication process and subsequent assembly of the PCB with components... Most designs are carried out by teams of people due to the complexity of many of todays designs, EEs for the circuits, software, firmware, DSP programing, PCB designers etc. I know many good EEs who would not appreciate being called half a$$ed because they prefer to sub the PCB design to a PCB designer... The days of people sitting nest to some one drafting a design are long gone
I tend to call it team work. Any significant engineering challenge will require teams to deliver. Layout people sit with the designers.We called that, through it over the wall layout
using a third party usually lengthened the pcb time frame because there were many back and forth reviews of complicated layouts.
Not at all. It's a trade off. I have a friend who is so mistrusting he even has his own pick and place, EMC chamber etc. He doesn't sleep much though.And that is the bean counter telling me how to do my job
Some like to play to their strengths. Some think they are Tony Stark. Takes all sorts.
For the record, Teflon is a bit 'over the top' these days, but not so much, 20 years ago when people (like me) were experimenting with using it for both EQ caps and circuit board material. Today, I might use Rogers or its equivalent.
However, everybody seems to ignore the real reason we used Teflon for circuit board material: CIRCUIT HOOK
A term used by Tektronix denoting a problem that they had with their attenuators, etc using normal fiberglass board material. This was described in an article in an engineering design magazine about 40 years ago. It is related to DIELECTRIC ABSORPTION and the Dielectric Constant which can be very high value in cheap board material. Air or vacuum is still best, but Teflon comes in second. That is why people were willing to use Teflon, and I'm not sorry that we used it. No problems so far with it, but it is softer and more expensive than most other materials.
As the Blowtorch runs at constant temperature, due to the fact that it is in a 'sealed' case and running 24 hours/day, no problems with Teflon have ever come up in the Blowtorch. Perhaps in autos, or other applications, it would fail in some way, I don't know about this.
BUT, low Dielectric Constant is key to ultimate design in this case.
However, everybody seems to ignore the real reason we used Teflon for circuit board material: CIRCUIT HOOK
A term used by Tektronix denoting a problem that they had with their attenuators, etc using normal fiberglass board material. This was described in an article in an engineering design magazine about 40 years ago. It is related to DIELECTRIC ABSORPTION and the Dielectric Constant which can be very high value in cheap board material. Air or vacuum is still best, but Teflon comes in second. That is why people were willing to use Teflon, and I'm not sorry that we used it. No problems so far with it, but it is softer and more expensive than most other materials.
As the Blowtorch runs at constant temperature, due to the fact that it is in a 'sealed' case and running 24 hours/day, no problems with Teflon have ever come up in the Blowtorch. Perhaps in autos, or other applications, it would fail in some way, I don't know about this.
BUT, low Dielectric Constant is key to ultimate design in this case.
Very few hermetic packages used these days, becoming a very limited niche area... Most common packages today are very similar to the base laminate for their X and Y CTEs, they have to be as more and more bottom terminated component packages appear every day and the compliance of a lead is gone, but a plus point is so is the parasitics of long leads between the IC die and the PCB.
All the information you want regarding PCBs is out there, its simple, just get hold of the IPC specs...
Very rarely sit with the engineer, well in fact never, usually in a different town, country or office.... Nothing worse than an EE sitting on your shoulder when you are trying to work....
All the information you want regarding PCBs is out there, its simple, just get hold of the IPC specs...
Very rarely sit with the engineer, well in fact never, usually in a different town, country or office.... Nothing worse than an EE sitting on your shoulder when you are trying to work....
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Yup, the material Tg is chosen these days to handle the assembly extremes vs the actual circuit operation.
Think about it, if the parts are packaged using epoxy then why would anyone have an issue with the pcb using epoxy
Now if you are using hermetically sealed packages then you are in a different league.
How many parts are packaged using epoxy? The bulk of surface mount parts I've used are ceramic (caps) or ceramic (resistors).
8 legged and 3 legged parts, while encapsulated with plastic, are dominated by the copper of the leadframe in the horizontal direction.
Ceramics run 6 to 8 ppm/C, copper is 16. G-10 I've used runs very close to copper below it's Tg.
My matched epoxies run 27 to 35 ppm/C below Tg, and greater than 90 ppm/C above the transition temperature. The bulk of my use is at 4.5K, all the materials described behave quite well from Tg to zero K.
John
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. 2.4GHz is boys stuff now.
Progress
Collision avoidance radar is 70-90 GHz and integrated solutions for parts of it exist.
Yeh, 20 years ago, doing boards for all sorts never needed Teflon, was even using a CAD system as the adhesive on my tapes had gone off due to being stuck unused in a cupboard for about 10 years.... Even then you would probably be hard pressed to measure ANY difference between a board running at AF on Teflon or FR4...
Again not been able to find much on circuit hook that isn't related to this thread and one or two others, fashion audio in my view.....
Yes.
In any case, note that the Tg for typical PTFEs is near room temp. They are very thermally stable, though, but there's no thermal stability issues with decent fiberglass-epoxy materials. Invoking the awe and mystery of Teflon is classic audiophile voodoo.
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