Archive for May, 2013

26
May
13

Easy toner transfer – after preheating the board

I posted this on the Yahoo QRP-tech group as well.

Regardless of toner or transfer medium, i.e. paper or plastic film, here’s a simple way to success.

Since I already had a $29 B&D Toaster Oven for solder paste re-flow, I decided to preheat the board and then run the board and transfer through the laminator.

1 – Preheat the oven to ~300F/150C.

2 – Turn on the laminator.

3 – If using plastic film, clear or Press-n-Peel, have a piece of cover paper ready. I just cut a sheet of printer paper to mostly cover the board and then folded it about 30% from one end, but the remaining 70% or so should completely cover the plastic transfer film.

4 – I then carefully laid down the transfer onto the board, and used the cover paper to rub over and flatten the film.

5 – While holding the board with pliers, align cover sheet with 70% on top and 30% underneath board and insert into laminator.

6 – One pass through the laminator to flatten under pressure is all that is required. Run board under cold water and peel off film.

The cover sheet is just used for the same reason it is when doing badges, which is where the idea came from. It just adds a margin of protection for the laminator and seems to make feeding the board seem easier.

The result was 100% coverage for both the paper and film transfer trials. Obviously (duh..) the higher board temperature at the start was key to getting the toner stuck down well.

Your mileage will vary, but this was neither cumbersome nor time consuming; especially using plastic film since there is no wash step. You are ready to etch!

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25
May
13

Circuit board toner transfer with Press-n-Peel

I received a 4 sheet order of Press-n-Peel┬áto try out this weekend. I first discovered this product via one of Fran Blanche’s videos on her PCB process. At the same time, a post on the QRP-Tech Yahoo Group alerted us to a rock-bottom price at Amazon for the GBC BadgeMates badge laminator. For a mere $10.06 and a Prime membership, you get a laminator capable of being used in the Toner transfer process. Unfortunately, I had to revert to a clothes iron as the GBC unit was not quite hot enough to use for Press-n-Peel and the $29 toner I am using in my HP LaserJet 2200. Well, the toner works well with paper…

Below is a close-up of the 3rd test transfer. Very crisp all in all which should produce a fine etch result. I have many more experiments to run before I have a process, but so far the results are promising.

Fine details of transferred image

Fine details of transferred image

05
May
13

Why are different types of capacitors used in various circuits?

Electronic experimenters often wonder why specific types of non-polarized capacitors are specified or used in different circuit types and whether substituting one type for another will make any difference.

The short answer is yes; a specific type can be the most attractive choice in an application because its characteristics fit the type of circuit it’s being used in. Cost aside, there is no best overall type of capacitor to use in all applications.

The longer answer is that a particular type of capacitor may best suit the most important characteristic that circuit requires of that capacitor. For example, in LC oscillator circuits, frequency stability is typically an important attribute for the designer. For a similar situation in which the LC circuit is being used in a filter section, the Q factor may be the most important feature for the circuit designer.

Along with cost, the long-term stability, temperature range stability (coefficient), Q factor, voltage coefficient, and value tolerance attributes of each type of capacitor technology varies considerably. Consulting manufacturer data sheets can help you choose which type or types are the best fit for you application. Below are some common types and why one might choose them.

Ceramic (NPO) – Best temperature stability, tight tolerances

Silver Mica – High Q/ high voltage range stability

Polystyrene – High insulation/Low leakage

Polypropylene Film – low self inductance and high tolerance

Polycarbonate – High dielectric strength (breakdown voltage)

Mylar Film – Low cost

These are of course just some of the reasons you might choose one of the above types, but availability and cost are often very important qualities to consider in any choice you make.