In a message dated 7/7/2003 4:05:37 AM Central Standard Time,
farnell_mark@... writes:
> paper phenol and epoxy. What are their characteristics? Which one is the
> best and which one is the worst? As a newcomer, which one should I try
> first?
Farnell:
Someone "in here" with far more wisdom on this topic than me will probably
have already answered, but as I was a "newcomer" once, and have never opened a
PCB shop in the years, since, so perhaps I can address your question with some
empathy:
Paper-based phenolic, similar to "Bakelite", is just as the name indicates,
layers of paper impregnated with phenolic-plastic, making a reasonably tough
insulating layer upon which copper film may be applied on one or both sides, for
making PCB's. It is "good enough" for radios and low-end home-entertainment
gear, etc., but I wouldn't want to find it as the "motherboard" material in a
$1000 PC or stereo! It can loose its electrical insulative properties when
overheated, as the carbon in it has a tendancy to separate chemically from the
other elements in the phenolic. I don't really know enough about the chemistry
to explain that further than that. But carbon is a fair conductor of
electricity when not chemically combined (see "carbon rod" in flashlight cells,
etc.), so this is not the swiftest stuff to use, but it's a few % cheaper than FR4..
.
FR4: Here, "FR" means "Fire Retardant". I think you are probably right
about the number following that, the "4" indicating the grade. FR4 is the most
common "glass epoxy" type of PCB stock in use, today. A couple decades or more
back, a material which LOOKED about the same, "G-10" was the "green stuff",
but it is not as good, so FR4 found favor and nudged out G-10, I understand.
The "green stuff" has glass fibers in it to strengthen it. It is only
coincidental that the initials can also stand for "Fiber Reinforced", but this is NOT
what the "FR" means, as I said in the first line in this ¶.
If you can ONLY buy "new stock" by the square foot, I imagine it is possible
the old paper-based phenolic may be a few pennies cheaper. But SO much FR4 is
being made and used, these days, for EVERYTHING, that its price is probably
close to cheapest. It may BE, for all I know! I don't know simply because I
make SO few PCB's myself, anymore, that I can get ALL the FR4 I need free of
charge from the nearest professional PCB house, when I go there in clean
clothing and beg. They said, once, that their machinery can't handle a "panel"
smaller than 4" wide, so the last 4" or so of a panel gets "wasted", and they
gladly give it to po' ignernt folk who beg sweetly.
Now, for a "newbie", the ONLY "advantage" I can imagine for paper-based
phenolic is that it might be kinder to small saws and drill-bits than FR4. If you
saw FR4 with a woodworking bandsaw (or ANY kind, for that matter, not having a
diamond-impregnated blade $$$!!!), the blade will go dull after 1" (that's
2.54 cm for our European friends!). Oh, a bandsaw blade might continue to cut
FR4 for some time, but after that first couple of cm, it won't do well on wood,
ever again! And HSS drill-bits will go totally dull in FR4 after, what, half
a dozen holes, and quit working at all after 20? Professional solid-carbide
PCB-drill-bits are simply the ONLY way to go, and they MUST be used in a
rather FINE drill-press, preferably with some clever means to prevent the slightest
sliding-about of the "blank", once you have it located exactly where you want
the drill to go. As carbide is VERY brittle, though harder than ANYTHING but
diamond, and if that blank "wiggles" at all, you will SNAP a $2 bit!
Some of the mail-order firms one can fine "in the back pages" of various
electronic hobby magazines offer carbide "regrinds" from time to time quite
reasonably, and if you GRAB a box of 50 of diameter, say, 0.75-1.0 mm, and/or an
assortment from, say, 0.6 to 6 mm SOLID-CARBIDE micrograin professional PCB
drill-bits, if you can find same for less than $0.75 (£0.50), you will have an
investment that can live for months, if you generally work carefully. Now, HSS
bits WILL tolerate a little "wiggle", but simply won't last long (unless you
regrind every few holes, and then they would get shorter so fast as to be of
questionable use at all!) Oh, carbide PCB bits all have 1/8" dia shanks! Yes,
even those used in Metricdom: 3.175 mm. dia. It might be easier to find a
high-speed "quill" with only an 1/8" collet, rather than a tiny adjustable
3-jaw chuck which would be necessary for the HSS bits of various diameters.
Look in the PC web-site's "FILES" section for "Home Made PCB Equipment."
Double-Click on that, then see the third file from the top. Double-click on it.
There you see my CNC PCB-drill run by a PET comptuter (still working fine
after its birth in 1976!) (The top-two files are discussion of what I did to
power the 400 Hz quill-motor). That's what laziness will inspire! Questions?
Lotsa luck and fun!
...P.S: Farnell? Any relation to the firm of that name in UK that sells
electronic goodies? Or, just coincidence?
Jan Rowland
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