printed circuit boards

[shellyfhl]

I'm a student doing a research project on PCB's (printed circuit boards) for my Digital Manufacturing class. I will be discussing the current technology used today for constructing PCB's and the future developments of ink jetting circuitry.

 

In regards to the first part of my project (today's method of making PCB's), I have been surfing the web all day to find a website that has a simple step-by-step procedure of how a PCB is built, but all the websites I have come across are so detailed and do not have a clear cut "list" of how a PCB is made. They all suggest different methods and I would like to know the general one that is used.

 

I am aware of a copper clad on top of the FR-4. Then i think the ink is put on top of this copper, which is then layered on by a mask. Some sort of light exposure process takes place and then the substrate goes into the etching phase. That is all I know, but I have no clue how to phrase it in a professional manner.

 

Can anyone possibly help me with this by listing for me the steps taken in today's process in developing printed circuit boards? And don't worry, I will definitely cite you as a resource, if you so desire.

[swansont]

This seems to be step-by-step

 

this, too

[shellyfhl]

Thank you Swansont.

 

Those websites were helpful and I will definitely use them as a source.

 

However, maybe I should have rephrased my question. I am looking for a step-by-step procedure of how professional manufacturing companies make PCB's. Just like the two website you referred me to, I also found many about "home-made PCB's" using irons and other household objects. Nonetheless, I would like to write my research project about the current technologies used in businesses, so that is a more professional representation and more accurate comparison with future developments (inkjetting).

 

I hope this makes sense.

[swansont]

I think your best bet would be to email some manufacturers. But if any of the steps are proprietary, they aren't likely to share the information.

[shellyfhl]

true. good point.

[shellyfhl]

I have been doing my research and have found books about PCB fabrication. Now, I am wondering...

 

1. Why haven't companies implemented inkjet circuitry yet? What is holding them back? Cost? Training?

2. Why would the cost be for this new application?

 

If anyone knows, PLEASE PLEASE let me know, thanks!

or even if you know of any articles/resources, that would be fabulous!

[5614]

PCB tracks are made of an electrical conducting metal which needs to be securely attached to the board... an inkjet printer requires the ink to be liquid... unless you heated the copper up a lot until it melted you couldn't print it like an inkjet printer does... and it wouldnt be cost efficient to heat it up that much.

[ezekiel23]

I seem to remember that there is in fact a method of using conductive inks to 'print out' a PCB. I'm not sure how exactly they do it in industry, but I'd imagine it would be with similar chemical etching techniques to home grown PCBs. Seems cost effective enough...

[5614]

Industry will always spend a lot of money finding the best and cheapest method. We may not know why, but trust me they'll probably have thought of it!

[shellyfhl]

inkjetting has definitely been an idea the past years. i think it IS just a matter of COST of why companies haven't implemented it yet. it would also take much time to study/research this new development.

 

i guess for the remainder of my research project, i am:

1. comparing the current process to the future inkjetting process and seeing WHICH steps inkjetting would replace

2. how inkjetting would be better than the current process...i found some articles about hazardous waste and environmental concernes regarding today's process.

[klanger]

I believe PCB's are made primarily from fibre glass, You know how when looking at a piece of wood you can see the grain? well it is the same with the fibre glass) the PCB is built up of many layers of fibre glass, each layer going in a different direction to give the PCB strength, and yet it still maintains some flexibility, (If you have ever tried to snap a PCB you will find it very difficult).

 

The layers are wet so once the pcb has been created as such it needs to be baked to dry out the water (though some water does remain, and may or may not reveal itself in the population part of the process). Next a layer of tin copper sheeting is placed over the pcb and secured in place using some kind of glue.

 

The company will have the schematics for their customers desired design and a stencil will be made accordingly, the stensil is placed ontop of the now blank PCB and acid is poured/squeegied on. The acid disolves the copper plating where it is not needed leaving behind only the reguired tracks that are covered by the stencil. The PCB then gets drilled (if its conventional through plate) and the little through plating tubes are inserted again using glue to hold them. The PCB is cleaned up and the tracks are painted with with something that can resist solder, then the whole thing is varnished to produce a smooth shiny surface, and if the customer has requested, the PCB may then be silk screened. This is usually in white paint and shows the outline of the components to be fitted and a location too, such as R1 @ l____l @ or D1 @ l_l___l @. The tracks and through plating are tested for continuity and then shipped to the customer. The drawing I just did is very crude but gives a basic idea of what you see, the @ representing the holes that the component leads go through.

 

Hope this helps, if its the population of the PCB that you require information on then please say so, as I can give you tips on that.

[YT2095]

have you done a search for Photo Etching?

 

they invariably use acetate sheets, the design can be silk screened onto it, and there`s no reason that an inkjet printer with the appropriate ink couldn`t be made to print the design onto acetate also

 

then it`s just a question of spraying the copper clad board with a photo sensitive polymer, laying the acetate sheet over it then exposing it to UV light for a little while. remove the acetate sheet ready for the next board then drop your exposed board into the etchant.

drill the holes, place the components and then flow solder it

 

simple really

[shellyfhl]

klanger, what do you mean "population of the PCB" ?

[shellyfhl]

i have figured out what i am going to write about now...

 

inkjetting can eliminate these steps:

-printing out the CAD drawing onto a sheet that is put on top of the board (what is that CAD drawing called again? the mask?) don't need this step anymore b/c inkjetting will allow the CAD drawing to be directly drawn onto the circuit board.

-no more need for applying photoresist

-no exposure

-no develop step

-no etching

-no more etching after soldermask is put on. inkjet can spray the soldermask on?

 

that is that i have so far. feel free to correct me or provide more info as to HOW inkjetting circuitry has more advantage over the current process of making PCBs.

[shellyfhl]

is the "silkscreen" the same as the "legend" ???

[klanger]

Shellyfhl to populate a PCB means to place all the components on it and solder it.

 

Components can be axial which means they have leads (bits of wire protruding from the body of the component) that actually go through the PCB, or they can be SMT (surface mount) which means that they actually sit on top of the PCB.

 

To solder these components in place there are various methods, traditional hand soldering (which is becoming a lost art, due to modern technics) wave/flow soldering, where a PCB with axial type components is passed along a conveyer that has built in ovens to gradually heat up the PCB and components before the underside of the PCB passes through a liquid bath of solder.

 

For SMT loaded PCBs a similar machine is used but this doesnt always involve liquid solder, though the two can be simulataniously soldered at the same time if the PCB happens to have a mix of both technologies. The solder is applied to the PCB in a paste format through a screen or stencil prior to the coponents being placed either by hand or automated machinery. The PCB enters a series of ovens on a conveyer belt, the ovens get hotter and hotter as the PCB passes along untill the paste reaches "flow" which means it goes from a gritty paste to liquid solder, the board then passes through various fans to cool down the PCB and make it safe for handling by an operator.

 

Hope that helps and isnt too confusing

[klanger]

Not sure about "legend", silk screen gives the operators a visual reference for placement and orientation of components but is also used in identifying the PCB itself, each PCB of exactly the same type will have an identifying number printed on them, such as 140-8900 this is so that you can look at the PCB and check it against your BOM (Bill of Materials ((all the bits and pieces that you will need to build the PCB)) to ensure you have the right PCB.

 

I think but am not totally sure, that the legend is probably this number reference, that number will be repeated on all necessary paperwork, purchase orders for the PCB, stores requisition sheets, production acceptance documents, BOMs, and drawings. This way the PCB can be tied in to all of them in a bid to eliminate the possibility of building the wrong PCB.

[shellyfhl]

thanks a bunch! definitely helped! =)

[nomadd22]

Dang. And here I've been carving out the copper with an exacto knife for thirty years. Somebody might have told me about etching before.

[jasonsioquim]

regarding that silkscreen question.

 

The silkscreen is the term used to name the layer w/c contains the legend.

The printing of the legend(component/board identifier) uses a silkscreen tool and ink to transfer the imge.

 

Jason