frgmnt org

24 June 2014

Downloads

Different workshop related downloads are available:

The illustrated Walkthrough of PCB Production shows how I do it in my electronics lab since 2007. I heard of & tried the toner method years ago – but for a long time was less successful in reliably producing nice quality PCBs. I tried photo paper, telephone book paper, color pages of magazines, dextrin covered paper, the various catalogs of  electronic supply companies. I tried different temperatures of the hot iron, higher & lower pressure. I tried different board cleaning methods, different chemicals, until I could cut “the chemicals” down to the etching agent & maybe isopropyl alcohol (a cheap vodka would do as well).  Of the etchants I tried two: Ferrum-III-chloride  (FeCl3) & sodium persulphate (NaS2O8) but want to try etching with copper-II-chloride (CuCl2) as an e-friendly closed cycle alternative. Now here is my recipe at the moment:

PCB-Production-Walkthrough <- updated

My Website´s logo was inspired by a traffic sign I saw on the Belgian Autobahn some years ago. This little graphic adventure is some vectorgraphic work I did about signs for ice, frost & snow flakes & permutations thereof. If the “real” Belgian ice warning sign looks like I recall it, I could not verify despite devoting some effort to searching for it.

The long awaited reader reader for the CTM 2010 workshop, includes schematics & layouts of the shown circuits:

Here I made a quite useful table of SMD (SMT) component sizes:

Typical SMD sizes

Even when using SMD, from time to time we need to drill some holes for through-hole-connections. I searched the web to find a better way before I start electroplating. Instead of using little bits of wire I found a novel way, which at least for me is 10 times faster:

Thruhole Fabrication

This is a short intro handout for successful circuitbending (auf deutsch) :

This is the handout from a workshop in xxxxx, Berlin, a VGA-monitor as wave display:

In summer 2009 I had a discussion with a friend of mine Andrzej Wróblewski aka Bohomaz, stencil artist, about vector based pattern generation. This inspired me to do some visual studies in spirographics. Here you find some full resolution pdf – especially the first is a bit heavy in pdf rendering – but hey, it is A3 and easily can be printed out in A0 (all are Creative Commons 3.0 BY-NC-SA licensed):

Spirographic-Study-II

This is the Schematic & PCB artwork for an STK4241 2x120W PowerAmp:

This is the Schematic & PCB artwork for a tiny LM4895 1W SMD PowerAmp  (only chip + four 1µF caps!):

Today Sergio from Mexico found an old documentation of a sequencer I made in 2007 for Piksel Festival. It contained several small errors, so here is the updated version of this nice 8-Step-Sequencer. It is simple but yet has some extra features. With a 150ohms resistor as current limiter. the sequencer can drive up to 20 milliamps to give pulsed electricity to filter circuits or toys.

Give it a try! Please NO commercialisation – especially of the gate circuit, which really works despite being so simple. Contact me if you need a custom extended version, there are several more astonishing tricks..

8-Step-Sequencer Schematic

Here is a simple Parallel Port Programmer for Atmega Microcontrollers (Schematic & PCB):

AVR DAPA-Programmer

A KiCad-Tutorial - KiCad is an open source software suite for electronic design automation (EDA) – designing schematics of electronic circuits and printed circuit boards (PCB). KiCad is developed by Jean-Pierre Charras, and features an integrated environment with schematic capture, bill of materials list, and PCB layout.:

KiCad-Tutorial

A Triac Tester - Had to work on a dimmer pack recently, I used & want to share this:

Triac-Tester

A Bat Detector - This thing works using only one chip, still EXPERIMENTAL:

Bat Detector

A Making your Life as an Artist - An eBook by Andrew Simonet, worth reading from about page 50 on:

Life as Artist (eBook)

*****

1 November 2013

A Soldermask for free

Filed under: specific — Tags: , , , , , — .. @ 03:08

Here I show your how to integrate some new steps in your photographic PCB-production process.

After the usual step of exposure with a positive of your track patterns & development & etching you just add another exposure with a negative of your solder mask pattern. As a result you get the rest of the etch resist as solder mask to stay on your PCB as protection & solder repellent. The idea comes from a Bungard datasheet.

Soldermask

21 May 2013

NaPS Etchant Chemistry

What is happening in my Etchant? ..and what should

My etchant of choice for PCB production is sodium persulfate (Na2S2O8). Chemists call it sodium peroxosulphate, short form NaPS, sodium persulfate is its trade name, the salt of peroxodisulphuric acid. It is a strong oxidizer. It is a severe irritant of the skin, eyes, and respiratory system. It is almost non-hygroscopic and has particularly good ability to be stored for long time. It is easy and safe to handle. It is not combustible, but releases oxygen easily and assists combustion of other materials. (Wikipedia)

Since copper is quite a noble metal it is not easy to etch with just an acid, it needs an oxidizer like NaPS.

A typical PCB etching solution contains:
• 1000 ml water
• about 250 g sodium peroxodisulfate
optionally you can boost the etching rate by adding a catalyst:
• 1 ml HgCl2 solution (about. 5 mg Hg) Degussa company recipe, but we don´t want mercury
• use silver ions (Ag+) instead as silver flakes or some drops of silver nitrate solution (AgNO3).

Etching process should be carried out in the temperature range of ca. 40 to 45 °C – higher temperatures lead to higher decomposition with the release of oxygen gas.  About 40g/l of copper can be dissolved in the etching solution, that is all the copper on 10cm * 127cm of 35µ PCB and approx. 6 kg of sodium peroxodisulfate are needed to dissolve 1 kg of copper. The copper and sodium peroxodisulfate content in the etching solution can be determined by the usual analytical methods i.e. colourimetry.

In sum the etching reaction mechanism is: Cu + Na2S2O8 ->  CuSO4 + Na2SO4

The ionic equation for this redox reaction is: Cu0 +  [S2O8]2+ -> Cu2+ + 2[SO4]2++ energy

We can write this overall reaction as two half-reactions:

the copper oxidation reaction: Cu0 -> Cu2+ + 2e-   with E0 = +0.340V

and the reduction reaction of  peroxosulphate to sulphate: [S2O8]2+ + 2e- -> 2[SO4]2+   with E0 = +2.010V

From the solubility curves of the components we can guess that the clear crystals are, which sometimes precipitate in older solutions – sodium sulfate:
Sulphate Solubility Graph

 

Waste water treatment & Disposal of etching baths

For waste water treatment the spent etching solution should be diluted in a big container & steel-wool added.

Etching solutions containing Cu ions, which are highly toxic to fish & bacteria in the biological stages of your city´s wastewater treatment plant and must not enter drains. The copper content of the discharged wastewater must not exceed a value of 2 mg per litre. Etching baths must therefore either be disposed of as hazardous waste or be prepared so that this limit is met. Since etching baths are treated as inorganic laboratory waste, the special disposal is very expensive.

It is therefore worthwhile to reduce these costs significantly by processing the solution yourself.

Processing: Etching baths are diluted to double the volume. Fill a maximum of three quarters of a 2l bottle & add steel wool (size 00, available at hardware stores) – this reduction will happen:  Cu2+ +  Fe -> Cu + Fe2+ , what means we get metallic copper & iron sulfate in this reaction: Fe + Na2S2O8 ->  FeSO4 + Na2SO4.

Steel Wool

It is exothermic – so be careful not to add steel wool too fast. The solution is allowed to stand for 3 hours, adding bits of steel wool, until they no longer dissolve & the reaction is complete. During this time the colour changes from blue to the pale green of Fe(II) ions.  Take some ml of the liquid & mix it with 1 ml of concentrated ammonium hydroxide (NH4OH): If no blue colour appears the copper concentration is below the permissible level for waste water discharges. If a blue color occurs, the process must be continued with more steel wool.

Cu-waste

Before & after this Process

If you have time allow the yellowish-green solution to stand 1-2 days in an open container or by passing air to oxidize the Fe(II) ions to Fe(III) ions. This step is not really necessary. The solution can then be added to the waste water. It only contains non-toxic iron-, sodium- & sulfate ions.

Decant the solution or filter out deposited copper (eventually together with sodium sulfate crystals) then let dry and place in a sealed polyethylene bag as household waste, metallic copper is no more toxic….

Copper residue, Sodium sulfate crystals above

28 April 2013

Advanced SMD Soldering

Since I wrote “Secrets of SMD” it is now more an a year. At that time a soldering iron was my favourite soldering tool. In between I tried table grill ovens and a pizza skillet (=electric pizza pan) as reflow device. Success rate varied a lot with molten dark parts (=high absorption) & unsoldered silver ones (=low absorption), no possibility to interfere in the running process & generally quite dark PCBs (overheated boards).
Today I mainly use SMD soldered on a clothing iron, use a hot air gun for the back of double sided or very simple single sided PCBs & the soldering iron mainly for small corrections or soldering connectors.

This is an overview  of my recent process of DIY production of PCBs. I hope it is not too sketchy, cause I do this write-up in the pauses of board making with exactly this process – I am quite new to it – it´s fresh!

See it is a starting point for your own fast prototype-production or just a way to share some ideas.

Toolz of our Business

First we have the hot air gun, a gas burner with catalyst, you can get it for about 20 EUR. Its useful for any re-work (de-soldering & repair) of multi-pin devices. Be careful not to overheat parts.

The hot air gun

The Hot Air Gun

Hot air gun, catalyst glowing

Hot Air Gun, Catalyst glowing

Next comes a hot plate, which can also be an electric pizza pan I used before. A clothing iron has the advantage that you can also use it for the toner PCB method or heating etching solution, it´s flat & heats up very fast. Fix it to a table with a clamp in a horizontal position:

Clothing iron fixed to table

Clothing Iron fixed to Table

Next we need hypodermic needles for the application of solder paste. I prefer the black 22G size, sometimes 20G. (Updated with this nice table)

Table with Needle Colour Codes

Table with Needle Colour Codes

Hypodermic needles

Hypodermic Needles / CC 3.0 Attribution: Zephyris

For breaking the needle I scratch the surface with an electronic cutter, rotating the needle several times:

Needles cutting

Scratching the Needle Surface

Then it is like breaking glass tubes, pull & bend at the same time:

Breaking a Needle

Breaking a Needle

After deburring on sandpaper or a sharpening stone we get a nice blunt shortened needle – as syringe I use a 1ml size with a silicone stopper, types with plastic stopper do not have a smooth action (the needed ones are sold as “latex-free” insulin syringes):

Cut needles

Cut & deburred

Against drying out of the solder paste I store the filled syringes in an old marmalade container with a tight lid, some drops of IPA (Iso Propyl Alcohol) or pure ethyl alcohol are added, the cap I shortened by melting with hot air:

Syringe Container with Alcohol Vapor against drying out

Syringe Container with Alcohol Vapor against drying out

Materials

Flux is used to cover the PCB before soldering. I produce it in two forms, as a liquid and with a honey like consistency by dissolving violin rosin in IPA. 1:10 volume ratio for the liquid, about 2:1 for the paste, which means dissolving as much as possible in warm IPA. Crystallisation forming the paste occurs on cooling. It´s more like making jam.

DIY Fluxes from Violin Rosin

DIY Fluxes from Violin Rosin

Here is the cheap Chinese solder paste I use. I guess it is meant for silk-screening. Adding IPA drop-wise may be necessary to get the heavy sticky liquid state we need for our purposes.
If you know some really good lead-free solder paste I may switch in the future. But most probably the 20..30°C higher process temperature needed will force us to use some different techniques.

Solder Paste

Solder Paste

Experiment!

I almost forgot the most important point: Try out things to get a feeling for the process & check your materials.
In this example you can see how I marked two cleaned areas, one with the excellent “Mechanic” solder paste to the far left, the other area with a more “professional” paste which needs a totally different process & does not work here.
In the right area I tried my first needle looking for dot sizes & how the paste performs on  a oxidized/uncleaned copper surface:

Experiments with Solder & Fluxes

Experiments with Solder & Fluxes

Solder Paste Application

A little drop of solder paste is squeezed from the blunt needle and applied as a small dot on the PCB. Pointed tweezers are helpful in placing SMD parts.
(BTW: I don´t  like comments like “your fingernails need cutting” – no, they are useful for work!):

SMD Placement

SMD Placement

On complex boards, think strategically. Try to put fine-pitched parts (small distance between neighbouring legs) first, you may have to correct their placement a lot or even to wipe off all their paste. This is hard to do in a stuffed corner.

All two-terminal parts are easy – I just apply paste for the next two to five parts & drop them in position. I don’t know if that is necessary or even harmful, but I press them down a bit – I don’t want to loose parts when handling the board later.

Bulky parts come last. They are always in the way & it needs more concentration to not touch them erroneously.

Solder paste applied with 0603 SMD parts

Solder Paste applied with 0603 SMD parts

Reflow:

First we need to bake the paste for some minutes. I use 10mins on “Silk” then heat up 20secs to “Cotton” – here the solder paste smokes a bit, the flux does its cleaning & flowing. Finally boost up to “Linen”.

Then reflow (= melting) occurs, stay there 15secs, eventually pressing down the PCB with some pointed instrument like a small screwdriver for to reach peak temperature. Then slide off to an unheated non-metallic surface to cool down slowly. Listen to the clicks of the iron´s temperature regulator, they give acoustic feedback of the temperature you reached. Use no steam :-)

At the reflow point you may notice several wonderful things: surface tension of the molten solder pulls together smeared solder paste & parts start sliding a bit to “click” in position if unprecisely placed. This sliding effect depends on the board design – datasheets provide you with optimized PCB patterns for this to happen if you run into problems with your design program´s generic patterns. Don’t expect everything to work the very first time.

Some caveats: An over-rapid heat transfer can cause solder splattering and the production of solder balls, bridging and other defects. If the heat transfer is too slow, the flux concentration may remain high and result in cold solder joints, voids and incomplete reflow.
When I have to deal with through hole connections I put aluminium foil under the PCB.

Reflow on the hot iron

Reflow on the Hot Iron

Success!

Finally check for shorts between adjacent IC legs. SMD-probes are useful. In any case do a visual inspection with a magnifying glass, I use a 6x & have the feeling 10x is best for our work.
Because our flux is pure rosin, it is “no clean” and can stay on the the final PCB. Cleaning with IPA and a toothbrush is also possible.

Finished soldering

Finished soldering

Creative Commons 3.0 BY-NC-SA (C)opyright : frgmnt