Perf board
 

..as in 'perforated' boards.

A recent thread on the use of op-amps mentioned the problems that can arise from using veroboard in HF circuits and high gain circuits but what are the practical limitations of the various types of perf board that are around?

I ask on the basis that I'm hoping to use a type of perf board that comprises individual holes on a 0.1" matrix - the copper is in the form of individual, isolated, square pads whilst the reverse is a full copper coat.

The intention is to build an HF receiver circuit based on the NE612 with a 4.9MHz IF and use the copper plane as a ground. Components will be laid on the 'pad' side and earthing achieved by soldering thru-hole wires to the plane.

I can achieve incredible component density using this technique (standard components, no SMD) and the small size is a particular requirement hence the reason for this method.

Will this arrangement be adversely affected by the use of such perf board? Would I have to remove the unused 'lands' to increase stability or any other construction techniques?

What are the limitations of the usual perf boards we find in common use?

Re: Perf board
 

I have used normal veroboard with strips one side successfully for low RF frequency designs i.e. 455KHz IF etc, but try to remove as much unwanted copper as possible. I have used the plain board with no copper on for VHF up to about 150MHz with no problems also. I have never bothered with the ground plane type, so no experience good or bad there unfortunately. I think you will get away with what you are proposing as long as you follow normal RF techniques. I have never bothered measuring capacitance between tracks before. I would imagine it will be low as long as the tracks are kept short.
Alan.

Re: Perf board
 

The groundplane will help you a lot.

As far as veroboard goes, it is not the frequency you use it at that creates the risk, it is the frequency capability of the devices you use. Of course, the layout is a big factor as well.

David

Re: Perf board
 

Just to add, just because the design is targeting 5MHz doesn't mean it doesn't have several "accidental" oscillators running in the VHF region at the same time. The construction method can result in all sorts of weird behaviour. It's amazing when you first hook up an RF amplifier or something and wonder why the current is higher than expected resulting in much head scratching. Pop a scope on it and things are a little fuzzy. Out comes the GDO and "ooh it's oscillating at 7MHz AND 125MHz". That is if it hasn't exploded by then. This problem is quite bad when you think your average bog standard jellybean 2n3904 has a transition frequency of 300MHz. They can even oscillate quite happily at higher frequencies than the transition frequency annoyingly.

There can be a couple of pF between parallel conductors on stripboard, at 5MHz that's a reactance of ~16k which is probably not worth worrying about in a lot of cases compared to bias impedances. Out there at 125MHz, ~600 ohms which may result in some interesting feedback loops appearing, phase shifting and consequential oscillation. Padboard/veroboard is a similar story. All sorts of crazy gets out.

IMHO the best compromise on density and not being too ugly is using single sided copper upside down so the ground plane is on the top. You drill the holes through for the parts, soldering grounded leads to the top surface. If you don't want it grounded, you remove the copper around that hole with a larger drill bit, pass it through and do rat's nest on the bottom side. Good until you enter UHF when you need striplines and other black magic I avoid like the plague. I've had to use this for all the PLL and frequency synthesis experimentation I've been doing to keep things stable.

Re: Perf board
 

Might seem a bit archaic, but it might be worth getting some copper /bronze MINI nails ( shoe repair places use them, )and sticking circuit on these on a bit of MDF.

Re: Perf board
 

out of interest, can you say where you get this perf board with a groundplane from? I've heard of it but never seen any?

Martin G7MRV

Re: Perf board
 

I think I've seen it on eBay - there's a vast choice of strip/perf board there.

Re: Perf board
 

I recently ordered a double sided FR4 epoxy glass stripboard (one side of which is a continuous ground plane) from RS Components using Stock No.100-4182.

Mike
M1DPB

Re: Perf board
 

Yes. it's an eBay item. I've used it for many analogue builds recently, mainly for the component density capability.

The picture shows the receiver board I'm constructing (I've used the copper plane side for the components and point-to-point wiring under) that measures 3" x 2". The missing parts are the NE612's and a couple of resistors to complete.

Re: Perf board
 

Think ive found it, sold by dar-tec?

Not cheap! But then, cheaper than a dedicated PCB!

Re: Perf board
 

I've used a similar type of board for RF prototypes up to around 100MHz with both SMD and through hole components.
Pic is of a 50MHz counter using ECL10000, HCMOS, PIC devices in DIL packages together with SMDs.
(Small PCB is 1GHz prescaler - I wouldn't try that on perf board).:)

Jim

Re: Perf board
 

Have you come across QRPme pads? (Google "QRPME", no connection, and other search engines are available.)

They're very thin FR4 boards, scored to snap off into individual bits ranging from single quarter inch squares through adaptors for DIL or SMT ICs right up to adaptors for valves (Octal, B9a, B7G).

They allow all these components to be surface mounted on a ground plane and hand wired, and, in the case of tiny SMT devices, increase the lead pitch to make wiring them into a circuit easier.

I think it's called Manhattan Construction, much better for HF than Veroboard. And with all the components and the wiring on one side, it's easier to debug and modify.

Stuart

Re: Perf board
 

Those QRPme pads are a little expensive. Even at G-QRP club prices. Manhattan construction really does work well though.

I've done a fair bit of "stingy" manhattan construction because I don't want to pay for QRPme pads. Rapid Electronics sell 100x160 (and larger) FR4 boards for not much money (or you can pay through the nose for CIF ones on RS). If you score both sides with a stanley knife then break a 5mm strip off with some pliers then use some tin snips/aviation shears to cut lengths off as you need it and stick 'em down. To do DIP packages you can use a square cut off with some traces hacksawed out and solder the IC or a DIP socket to it:

Attachment 142934

The above was receiving a £8 log amp IC so I wanted to be nice to it :)

Re: Perf board
 

A company called Crownhill Associates do a range of pcb materials for very good prices that range from 3mm to 0.2mm in thickness - single and double sided.

I've used the thinner stuff in a hole punch to make small 'disks' that glue onto another substrate for point-to-point soldering techniques.

It's also very easy to cut to any shape with scissors.

A roll of adhesive copper tape is also in my store for the odd occasion that requires some screening or particularly convoluted routing.

My only other concession to manufactured parts are a set of SOIC-to-DIL adapter pcbs for when I can't obtain the usual IC's in DIL format any more.

The last pcb adapter I purchased was an edge connector that allowed me to use 0.1" headers with a 0.7mm pitch ribbon cable (50-way) so I could remotely mount a small LCD screen on my SDR receiver.

Re: Perf board
 

I suspect there's an element of "horses for courses" when moving up from Veroboard.

The perf board with a ground plane (and ideally a power plane, especially for certain TTL families) will be good for logic, with a regular array of 0.1" DIL devices and decoupling caps, but the Manhattan construction over a ground plane, possible modular, has advantages for RF/Analogue, where you may have devices such as coils, filters, crystals, etc with leads not on 0.1" pitch, and you may need to add extra components such as stoppers or decoupling and specific parts of the layout.

On a related topic, you need to be careful of using sockets for some ICs, the extra impedance in the power and ground pins can be a killer.

I have some QRP meTube panels as well as some SIOC "expanders". I fancy having a go at a TRF, with a valve regenerative detector and an SOIC for the audio.

Stuart

Re: Perf board
 

A couple of decades back [well, to be honest maybe more than three] I did quite a lot of VHF/UHF prototyping on double-sided PCB material - laying it out as "stripline". Sometimes this involved crazily-serpentine traces when aiming for resonance below 200MHz.

The big issue was always "will the next batch of PCB-material have the same self-capacitence as the last" ?? And to be honest it was not consistent so we switched back to specifying "above-the-plane" silver-plated coils [some of which were just a 5mm half-loop] because these were repeatable irrespective of which minimum-wage oriental fab-shop got to stuff them into the PCBs]

Re: Perf board
 

I used veroboard in my college project microprocessor system (4 boards including power regulation each plugging into backplane - 1MHz clock). College staff were skeptical but it ended up being very reliable even when powered up recently after more than 25 years).

When playing with minature VHF FM transmitters I have used such board but obviously low power / non critical.

In my experience, tidy construction and thought given to possible issues (resulting in removal of tracks / links which may give unwanted inductive or capacitive effects) can make all the difference, but, as I found with my microprocessor system, expect some initial teething troubles in which the reason for poor operation is often not obvious.

Re: Perf board
 

When I worked at Bradford Uni in the 70's..... we had a visit from a Rep.. I think from Vero who had some interesting samples..one was a 300 x 300... 0.1" pitch with a plain copper topside with the normal strip underside. He gave us 2 boards for evaluation. Great for RF and other critical circuits. Unfortunately Vero did not continue this product.
I still have the remainder of the "left overs".
Although I use pcb for all my construction now.. its there... just in case