The PTH Printed Circuit board manufacturing process.
CAD File processing
The PCB CAD files (or Gerber files) are sent to the manufacturer by email
The PCB manufacturer has their own pre-production inspection of the files at which they add a drill list and identification
The CAD files are rasterised and photoplotted to make film artwork
Laminate drilling and electroplating
The process starts with bare laminate material - usually FR-4
The laminates, (with copper on both sides, but no pattern yet) are drilled with holes. For reasons of economy, the laminates are larger panels that often contain several PCBs
The drilled laminates are coated in a chemical to enhance electroplating of holes. This is usually done using a multistep process called electroless copper.
The laminates are put in a copper plating bath, all the holes are electroplated. This connects pads on opposite sides of the PCB, electrically, through copper in each hole.
Laminate etching
The laminates are coated with a UV-sensitive photo-resist
The track pattern is imaged onto each side of each PCB, using the photoplots and UV light
The photo-resist is developed, leaving photo-resist only where copper is required
The laminates are put in acid, to etch away unrequired copper, forming the track pattern
The bare copper PCB, with tracks and pads now finished, is cleaned
Laminate solder masking and tinning
The bare copper PCB is silkscreened with a solder mask (usually green)
(Sometimes the solder mask is applied by photoimaging or dry film)
The solder mask is dried or cured
The PCB is tinned - solder is applied to exposed pads
The PCB is levelled - bumps in the solder are made flat by using hot air
Final stages
The PCB is silkscreened with component Identification lettering (usually white)
The silkscreen legend is dried or cured
Any final drilling is done of holes that are not to be plated through, any routing is done, and the laminate is cut into individual printed circuit boards
Click the Continue arrow below for "Prototyping," or go on to:
How to design
by Rudy Sedlak
RD Chemical Company

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Episode 15 - PCB Etching
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There are other ways to configure the outerlayer manufacturing process, where the circuitry is protected, during etching, by photoresist, instead of a metal etch resist. In this case, the etching process more resembles the etching of innerlayers, which is covered in Innerlayer Process Fabrication, Etching.

Tin or Tin/Lead is the most common etch resist used today. The use of Tin or Tin/Lead as an etch resist essentially mandates the use of ammoniacal etchant, because this is the only commonly used etchant chemistry that will not attack the Tin or Tin/Lead. When the term ammoniacal etchant is used here, it will refer to Ammonia/ Ammonium chloride etchant chemistry. There is also an Ammonia/Ammonium Sulfate etching chemistry that is commercially available. The Sulfate based etch chemistry is used to facilitate plating out of the copper from the etchant, thus allowing on-site recycling of the etchant. This sulfate based chemistry is not widely used, because it has a very slow etch rate, which would be expected in a non-Chloride etch chemistry.There has been some attempt at using Hydrogen Peroxide/Sulfuric Acid etches to etch outerlayers. This process has not been widely accepted commercially for various reasons, including economics and the issue of disposal of the spent etchant. Further the Hydrogen Peroxide/Sulfuric Acid etch process will not allow the use of a Tin (only) etch resist, and thus usually will require a Tin/Lead etch resist. This fact will make Sulfuric/Peroxide even less attractive, as the move to eliminate Lead from the printed circuit board manufacturing process becomes more widespread.

Etch Quality, and Pre-existing problems
The quality of etch can be minimally defined by the completeness of the removal of Copper which is not protected by the etch resist, and no more than that. However the definition of the quality of etch, in reality, also includes the straightness of trace edges, and the level of etch undercut. Etch undercut is a result of the fact that the etchant is not inherently directional, and will etch sideways as well as downwards.

Etch undercut, (See Figure 4) is frequently discussed in terms of "etch factor", which is defined as the amount of etch undercut divided by the amount of Copper that has been etched through ("X" in Figure 4). The PCB industry varies widely in its etch factor, and factors of from 1:1 to 1:5 are seen. Clearly, less undercut, or a lower number of the etch factor, is preferable.

The etch factor, or the level of etch undercut, can be affected (it may be optimistic to say it can be controlled) by etch equipment configuration, and by the etch chemistry. Chemical agents called "banking agents" are present in the etch chemistry to minimize undercut. The exact nature of these additives is usually a closely guarded trade secret. Etch equipment configuration to minimize undercut will be discussed later.

In many ways, the quality of etch is already defined before the PCB enters the etch chamber. The PCB manufacturing process is closely inter-connected, no one step stands alone. The result is that many of the problems that are diagnosed as "etch quality" originated in the resist stripper, or even previous to that in the process. The outerlayer etch is perhaps more prone to the deterioration of quality because of "upstream" problems in the process than most steps in the PCB manufacturing process. This is because of the fact that outerlayer etching is the last in a long series of steps, beginning with photoresist exposure, which define the outerlayer circuitry. Clearly, the more steps in a process, the more things can go wrong. This seems particularly the case in PCB manufacturing.

The PCB, in theory, arrives at the etcher with a cross section pattern that looks like Figure 2. The optimum situation in the manufacturing of a pattern plated PCB is that the combined thickness of the Copper and Tin or Tin/Lead plating does not exceed the thickness of the Photoresist, and thus remains completely within the "well" defined by the walls of the photoresist. However, in the high pressure world of PCB manufacturing, it is common for the plating on certain areas of the panel to be excessive. So excessive in fact, that the plating extends over the top of the photoresist. When the plating is this much in excess, and it extends over the top of the photoresist "well", it extends sideways also, and herein lies the real problem. This sideways extension creates a "lip" of Tin or Tin/Lead etch resist which extends over the top of the photoresist (see Figure 5).

This lip of plated Tin, or Tin/Lead, etch resist makes complete removal of the photoresist during the resist stripping process prior to the etch, extremely difficult, leaving unstripped photoresist residues under the lip of metal etch resist. (See Figure 6). Residual, unstripped, photoresist can cause incomplete etching, which will be evidenced by a copper "foot" next to the trace after etching. The presence of this foot effectively narrows the space between the traces, and this can ultimately cause the PCB to be out of specification, and cause rejection. Rejection of the PCB at this point in the process is particularly expensive because most of the work (read "cost") to produce the board has already gone into it at this point.

In the extreme case, residual photoresist can also cause a build up of scum in the etcher from the reaction of dissolved photoresist and Copper in the etcher, which can clog nozzles, pumps, and make it necessary to break down the etcher and clean it. Because of the powerful odor of Ammonia, this is one of the least liked jobs in the PCB industry, never mind the cost in production time.

Equipment, Setup and Interaction with Etchant Chemistry
The ammoniacal etch is one of the more subtle and complex chemical processes in PCB manufacturing, yet paradoxically it is also one of the easier to run. The current technology, once set up properly, almost runs itself. However it is a process that does not adapt well to shutdowns, and is best run continuously. The process is heavily dependent on well set up (and maintained) equipment. As in all chemical etching, the use of a high pressure spray with properly chosen and configured nozzles is critical to obtaining high quality etching of the copper with straight side walls.

There are many theories on the proper design and configuration of chemical etchers to obtain the straightest sidewalls, and many of them are conflicting. However all the theories agree that the basic concept is to get as much fresh etchant to the surface of the metal as fast as possible. Analysis of the chemical reactions of etching supports this outlook. In the case of the ammoniacal etch, assuming that all other parameters are in order, the etch rate is probably controlled by the availability of free Ammonia (NH3) in the etchant, and thus getting fresh etchant to the etch interface does two things, it sweeps away the just produced Cuprous ion, and supplies fresh Ammonia (NH3) to the etching reaction. Please refer to the Innerlayer Process Fabrication, Etching for a discussion of the chemistry of the ammoniacal etchant.

Among the "ancient" lore of the PCB industry, and especially of the PCB suppliers industry, is the fact that the lower the Cuprous ion content of the ammoniacal etchant, the better (faster) it performs. And this is confirmed by experience. In fact, many ammoniacal etchants have Cuprous ion specific ligands (complexing agents), to effectively lower the available Cuprous ion, as part of their secret for high performance. Further, the Cuprous ion effect is not small. Etch rates can be more than doubled by reducing Cuprous from say 5000 ppm to under 50 PPM.

Since Cuprous ion is being produced in large quantities by the etching reaction, it is difficult to keep the Cuprous ion concentration at near zero, and it is not made easier by the fact that the Cuprous ion is tightly bound in an Ammonia complex. The Cuprous ion is removed from the etchant by conversion to Cupric ion by reaction with atmospheric Oxygen. The Cuprous ion reacts with atmospheric Oxygen in the etch chamber, as the etchant is being sprayed.

This is the functional reason why air is drawn through the etch chamber. However if too much air is drawn through the etcher, excessive Ammonia loss will result, and this will cause the pH of the etchant to drop, which also causes the etch rate to drop off, confirming the fact that Ammonia is the rate controlling agent. To counteract this, some users inject anhydrous Ammonia into the etch sump. This is typically done using a pH controller, which operates by signaling for the addition of Ammonia when the pH falls below a preset point.

The allied field of chemical milling (also known as photo-chemical machining, or PCM) has produced some startling research into etcher configuration. And while the etchant used was Cupric Chloride, not Ammoniacal Copper etch, what was discovered should apply to the use of Ammoniacal etch in the PCB industry as well. The PCM industry typically etches foils that are 5-10 mils thick, and occasionally much thicker than that, consequently etch factor is even more critical than in the PCB industry.

One set of research, from the PCM industry, which has never been published, produced startling results. The research was well funded, and thus the researchers were able to make profound changes in the design of the etcher, and check the effect of these changes on the etch factor.

The optimum design was found to be one that used fan, as compared to cone nozzles, with the spray manifolds etch chamber, and thus etches quickly. The final part of the panel, however, will have a puddle on it as soon as it enters the etch chamber, and thus etches more slowly.

The top versus bottom side difference in etch quality can be compensated for by adjustment of spray pressures on the top and bottom spray manifolds. There are some innovative designs now being proposed to compensate for the leading edge problem, that shut off the first few spray bars for a time after a panel enters the etch chamber.

Etcher Equipment Maintenance
Perhaps the most critical factor in maintenance of an etcher is to insure that the spray nozzles are kept clean, and unclogged. Clogging can occur from the buildup of sludge in the etcher, or from bits of the PCB's being etched which are knocked off by the force of the sprays. If the nozzles are not kept clean, the etching will be non-uniform from side to side, thus producing reject PCBs.

Beyond the obvious maintenance of replacement of broken, and worn parts, including the replacement of nozzles, as they also wear, a key issue in etcher maintenance, is keeping the etcher free of sludge. Sludge can accumulate in many ways, and can even accumulate in an etcher where the chemistry is kept in balance. The sludge problem can get totally out of control if the chemistry is allowed to go out of balance. The magnitude of this problem is difficult to over emphasize. If the etchant does suddenly "sludge out", it is usually a sign that the chemistry of the etchant was allowed to get out of balance, and it can be cleaned up with reasonably strong Hydrochloric Acid, or with etchant replenisher.

Sludge can also be a buildup of photoresist, which, initially dissolves in the etchant, and then precipitates as a Copper salt. Photoresist sludge in the etcher is, of course, an indication that the photoresist stripping is inadequate. Poor photoresist stripping is symptomatic of marginal photoresist stripper combined with overplating.

Introduction
The first question that I can hear u thinking is what’s a PCB? PCB stands for Printed Circuit Board, for example your motherboard is one big PCB (just multilayered) obviously a motherboard is way out of our league, however with some household equipment and some chemicals we can make ourselves some great casemodding PCB’s. Just think of fading LED’s, homemade fan controllers, and anything else you can come up with. In this guide I’m going to explain how to make a usable PCB. With this step by step guide you can make you own in no time, here’s a list of things that will be needed.

Plastic Tweezer

Disclaimer: The information contained in this site is for guidance only. The application of this tutorial can differ extensively based on the particular items involved. The information on this site is provided with the understanding that the author(s) and publisher(s) are cannot be held legally responsible for any injury or death that may result from this or any other article at OCModShop. With this being said be sure to understand what you are doing before you attempt what is being shown. If you have any questions about any aspect of the article please contact the author or another experienced individual before proceeding.

A sheet of printable transparent film (for overhead projector usage)
2 plastic or glass containers to hold the liquids.
Plastic tweezers
0.8mm, 1mm, and 1.5mm drill bits
Water
Acetone, or nail polish remover (contains acetone)
A face toner, or any other UV-A light source
A blank PCB with UV photo layer
Some Hydrogen Peroxide (35% concentration but lower is also good)
Some Hydrochloric Acid (10 % concentration)
Caustic soda, which is also referred to as Sodium Hydroxide.used for surface preparation to the faster etches used for etching the tracks. Some are best used in horizontal spray process equipment while others are best used in tanks. Etchents for PTH work have to be selective and be non aggressive to tin / tin lead plating, which is used as the etch resist. Copper etching is normally exothermic, where high speed etching is carried out solution cooling is normally required. This is normally done by placing titanium water cooling coils into the etchent. Almost all etching solutions liberate toxic corrosive fumes, extraction is highly recommended. All etchents are corrosive and toxic, mainly due to the high metal content. P.P.E. Personal Protection Equipment must always be used, spent solutions should always be disposed of properly and not down local drains, where they pollute local sewage works and rivers.


For a more detailed chemical look at the etchents please follow the section menu links to the different types of etchent. When working with electronics, breadboards are a cheap way to put together circuits. Having professional Printed Circuit Boards made can be very expensive in small quantities, but the results not only make projects easier to construct but also make them look fantastic. While the cost of production is a great deterrent, for less then $20 it is possible to etch your own PCB.

There are two ways to etch a PCB: the Toner Transfer method, and the Photo Resist method. This article will examine the former method using common household items. Before you start you will need the following:

Access to a Laser printer.
A sheet of photo gloss paper.
A fibre glass copper coated board.
Ammonium Persulphate.*
A cloths iron.
Plastic containers.
0.8mm 1.0mm and 1.2mm drill bits and a drill.
Pliers
A hacksaw
Acetone or methylated spirits.
Some Fine grit sandpaper or a scotchbrite pad.
The following optional parts will also help improve the results:

A fine artwork knife, or scalpel.
A etch resistant touch-up marker.
A kettle.
A metal file
Some kind of small rotary tool like a Dremel instead of a drill.
A toothbrush
PCB solder-through lacquer.
* Ferric Chloride can also be used. For guides on etching with Ferric Chloride select the link at the bottom of this article.PCB Etching Equipment — Chemical Etchers
Printed Circuit Board
In 1957, Chemcut developed conveyorized, double-sided spray etching, a technique that made the chemical etching process practical for volume, as well as prototype production. Today, we are the world's largest developer and supplier of PCB etching equipment for advanced electronic interconnect fabrication, with more than 15,000 units in operation.

Chemcut systems integrate process equipment and process controls to fabricate high performance products, in high production volumes, with high yields. Our PCB etching and PCB milling systems are in production seven days a week, yielding over 99% quality printed circuit boards, and we remain uniquely skilled at providing solutions that meet or exceed the electronics industry's accelerating technology and productivity requirements:

Fine Line Etching – Process materials ranging from 2 mil core innter-layers to 250 mil multi-layers, and from flexible reel-to-reel Kapton to rigid FR4.
Chemcut PCB cutsomers are producing 2 mil trace x 2 mil space circuits at production volumes.
Thin Material Transport – For processing inter-layer materials. Chemcut offers a unique comination of conveyor wheels. Today's ultra-thin materials are transported without compromising the fluid delivery performance of the processing systems.
PCB Etching – PCB Fine Line Etching for Printed Circuit Boards
Need Assessment?
To determine the feasibility of chemical etching for your PCB production, we offer our laboratory service for Staedtler laundry marker. Direct to pcb InkJet Resist Printing

by Volkan Sahin and Stefan Trethan
This page details the modification and use of an Epson C84^ InkJet printer with MISPRO Inks^ (#MISPRO42-SET-MK) to feed and directly print resist patterns to copper clad printed circuit board stock, ready for etching.
You can skip to the section showing what you can do with the modified printer, if you like

Once you can feed the pcb through the printer for etch resist, you can then feed it back through the printer for solder mask (yes! Volkan reports that it works!) and for a component "silk-screen".

Toner transfer is probably easier to set up for and may be as fast, but direct ink is more precise, allows solder mask and component printing in the appropriate color, and it appears to be much more precise and repeatable, allowing for finer double sided boards without alignment issues. And if you admit that a laminator is required for TT, given the prices for old C84 printers^ and the Durabright / MISPRO Ink, direct to pcb InkJet printing is much cheaper.

The secret (discovered by Volkan) is that certain pigment based inks can be cured with heat to form a very strong resist. The Epson InkJet printer use pizeo electric actuators in the print head (rather than the thermal method used by other brands) which allows for different types of ink to be squirted out. The "Durabright" inks include a pigment rather than dye. For more, see: http://inkcityusa.com/epson_durabrite_inks.htm

This guide was written by Stefan Trethan and edited with comments added from Volkan Sahin (Volkan not Volan, Voltan, Votan, etc...) who first developed and shared this method on the Homebrew pcb Yahoo Group^.

Printer Modifications:
C84 by Stefen Trethan
Here is a nice shot of the final modified C84 ready to print. The guides are mocked up in this photo, but have been completed as planned.

Details here

Epson C63 C64 C83 C84 Printer Service & Repair Manual
$12.95 2d 14h 19m
Epson Printer Stylus C84 Ink printer
$9.99 2d 16h 53m


View all 9 items on eBay disclaimer

C87 by epineh^
. Check out the traces Russell is getting! That is a TSSOP chip!

C88 by wnnelson
I modded a C88 without hacking the frame. I made new bushings for the drive shaft which lowered it by .100". {ed: the new bushings were turned on a lathe to match the shape of the originals on the outside, and then an off center hole was drilled in the inside to hold the shaft in the lower position } I trimmed off {ed: turned down on a lathe} the outfeed rollers to give a flat carrier path and moved the paper sensor to the front. This allows a carrier with no cutout notch for the timing. {ed: because the edge of the tray now triggers the sensor} I put a smaller gear on the end of the drive shaft for the vacuum pump because there was no room for the original gear. {matching a gear like this can be quite difficult. If anyone knows the source of this gear, please share it} This causes the pump to run slower but does not seem to affect the operation. I hope this will help with the clogging problem as the cleaning station has not been modified. I added a little tubing to the pressure rollers to give it a little extra pressure as the carrier is too far away for the regular roller. So far it is working great.

CX4200 by Volkan Sahin
This is Volkan's modifed CX4200 as it prints a pcb. Details for modifying this printer are in the works.

Ink Cartridge Refill for EPSON printer cx5000 cx6000
$9.75 4h 35m
Ink Cartridge Refill Kit for EPSON printer C88 cx3810
$9.75 5h 43m
Ink Cartridge Refill Kit for EPSON printer C88 cx3810
$9.75 9h 43m better resist with less ink being deposited on the board."

Printing
Check out this great video showing how to use a modified C87 to print and etch a pcb.

READY

LOADED

To print you must insert the carrier manually into the printer. Turn the printer on, and wait until it has completed it's dance. Now feed the edge of the carrier into the printer so that it just protrudes a few mm from the traction/pressure rollers. Make sure it is straight so it will not run against an edge when the printer feeds. Now print the artwork on your carrier to find the right position (stick some tape or adhesive backed plastic foil on it or you may end up with permanent marking of the carrier). You can use low resolution for this print since you only need to know where it will end up. If you use the fastest draft setting watch out, the printer virtually shoots it through.

Now place the pcb over this position and stick it down with tape along the edges or using double sided tape underneath. You may delay the acetone cleaning of the pcb until this point if you prefer. Again feed the carrier and print the artwork.

Printer Settings
When printing a purely black test pattern I found the transparency setting does not use any ink from the black cart at all. The other settings use ink in varying amounts, the most ink is used for matte paper and the least for glossy or durabright setting. You need Photo or Best Photo resolution. The "fast" setting, which prints in both directions of travel, produces better results for me. No edge smoothing needed.

Screen shots of Stefen's driver settings for the C84: 1, 2
Screen shots of Volkan's driver settings for the CX4200: 1, 2
Curing

START

ALMOST

CURED

This is a key step. The pcb and ink must be heated at a specific temperature to cure it and keep it from coming off in the etchant. To do this, a stove or heat gun will not allow the required temperature control. Something more precise must be used: Basically an old electric hot plate with a aluminum plate on top and a temperature meter attached. It turns out that around 446F / 230C is the sweet spot. keep that for several minutes (at least 3 i'd say for now but more research needed). This incidentally is exactly the point where the copper will start to go from just minimal yellowish oxidation to a purple one (This is probably what Volkan is using to judge the temperature). It is well away from damaging the pcb.

If you are much below or above this temperature the ink will not resist so well. Round about 225C the ink starts to change somehow and can no longer be cleaned off with acetone.

etching
I suspected Ferric chloride is less aggressive to the [MSPRO] ink than CuCl, so i set up a test. I cut a test pcb in half after curing to get identical samples, and put one in CuCl and one in ferric chloride. If anything the ferric chloride showed more aggressive under-etching. In the samples below, the lines above 3 mills are fine; below 3 they are unreliable. For a certain number of projects, including first-prototype, surface mount 'breadboarding', layout
You only need a few boards, or are willing to live with a yield as low as 50%
Drill hole locations can be imprecise (up to 10 mils off!)
Conversely, when using the spray etcher is a bad idea:

You dislike wet chemistry/cleaning
Are using exotic substrates
There are many vias, or throughhole parts, and you dont want to drill holes/solder vias.
You want the boards to be perfect without checking for shorts or opens
You need printed overlays, multiple layers, through hole plating or solder masks.
You want many parts. Remember that for $200 you can just about get as many boards as your heart desires, and from a reputable PCB manufacturer.
Getting the Layout Ready
In this step you will prepare your layout for etching. For this step you will need: a quality laser printer, a sheet of transluscent paper.

The photoresist method we use in PCB etching is a positive process, which means that when UV light hits the resist, it softens, and then is washed away. What remains is a positive of the PCB design. What this boils down to is that you will want a positive printout of your PCB design (black where there will be copper). Preferably mirrored. Most all PCB design tools let you print out your layout mirrored. Or you can mirror your entire design in the software. Whichever. Also, if possible, have it print white holes where you will drill, these will be your drill guides. Because the drill holes will not be precise, make your annular rings (the copper around a drill hole) larger than normal. Since you will lose as many as half of the design to exposure/development/etching flaws, tile 2-3 times layouts as many as you want.

In Eagle: After your design is ready, go to the CAM Processor, and open the "layout2.cam" job. As output select PS. Change the extention to ".ps" as well. Be sure that Mirror is selected but that Fill Pads is not. Then open the ps with any free postscript viewer and print it. (Also you could print it to "Gerber274x" and use a gerber viewer, or any other format you can print.)

After you have verified the above, print your design to a high quality (600dpi at least) laser printer, in monochrome mode, onto a white piece of paper. Double check that it is as you want it, in the correct orientation, enough tiling, mirrored, dark ink, slightly smaller than the PCB you have, etc. Now print it onto translucent paper, there is a box of it in the cabinet underneath the etcher, in a thin cardboard sleeve.

Left, plain paper test. Right, translucent paper. Both are mirrored.

In this picture, I have two layouts I want to etch. I tiled one three times and one twice. The one I tiled three times has a very fine pitch IC (TSSOP-16) so it is less likely to come out. On the left is opaque laser print. On the right, translucent paper. Note that the design (noticably the text) is mirrored. How to Make PCB's
One of the most discouraging things about making a hardware project (apart from obtaining all of the components) is building the printed circuit board - PCB. It is sometimes possible to use strip board or some other pre-fabricated board but more often than not the circuit complexity and performance requires a proper PCB to be made. The good news is that due to improvements in printing and processing technologies it is now relatively easy to make inexpensive high quality PCB's at home.

WARNING: Making PCB's requires the use of Ferric Chloride (FeCI3) which is corrosive so avoid skin and eye contact. Remember safety first use glasses, gloves and protective overalls. Ferric Chloride is also very good at distorting cloths weeks after you think you have washed it off. If you do get any on your skin then wash it off immediately with lots of water and soap.

The Shopping List

This is the minimum things you will heed,

1. Access to a PC with a Laser printer eg: HP Laser Jet
2. Cloths iron
3. Kettle
4. Water bucket