Homebrew PCBs

Hello all,
I am looking to create my first homemade pcb using the photolithlgraphy method. I've read some tutorials on both methods and did some browsing on the board here, but I still have some questions.

1. Does negative dry film resist share the same characteristic of longer development times for aged film that pre-coated boards have?

2. Does negative dry film resist provide greater detail than positive pre-coated boards?

3. What are some advantages/disadvantages of negative dry film vs positive pre-coated boards besides the following?

-Negative dry film: Lower cost
-Negative dry film: Needs clean board/more steps required

Thank you,
Darren

dbrock178 wrote:
> Hello all,
> I am looking to create my first homemade pcb using the photolithlgraphy method. I've read some tutorials on both methods and did some browsing on the board here, but I still have some questions.
> 
> 1. Does negative dry film resist share the same characteristic of longer development times for aged film that pre-coated boards have?
> 
> 2. Does negative dry film resist provide greater detail than positive pre-coated boards?
> 
> 3. What are some advantages/disadvantages of negative dry film vs positive pre-coated boards besides the following?
> 
> -Negative dry film: Lower cost
> -Negative dry film: Needs clean board/more steps required
> 

I've never used pre-coated positive photoresist boards so I cannot 
comment. Does anyone know how this resists is applied, since I don't 
think dry film positive resists exist. All the positive resists I've 
come across are in liquid solvent.

I've use the old spray on Electrolube PRP photoresist , and all I can 
say is its a pita to use compared to negative dry film. Even when you do 
manage to get a uniform, contaminate free, well adhering coating, the 
stuff is lot less forgiving in the developer and exposure time compared 
to negative dry film.

Professional PCB manufactures exclusively use negative dry film 
photoresist. It must be economical overall, weather that's because it is 
easier to process with simple equipment or lower bulk material cost.

Since I had a real photolithography lab to play with, I could make some small boards. The resist was spin coated.  Basicallly gripped with vacuum and spun at a high speed for a certain length of time.  The ramp could be controlled somewhat too.

Exposure areas were small too because of the mask aligner which wasn't used.  Just the bulb and the timer.

So, I could probably make a 5' x 5" board.  Most were about 3" x 5"

There were a couple of bake steps.   Maybe something like, coat, bake, expose, develop, bake, etch.

--- On Mon, 3/16/09, Adam Seychell <a_seychell@...> wrote:

From: Adam Seychell <a_seychell@...>
Subject: Re: [Homebrew_PCBs] Differences between negative dry film resist and pre-coated positive resist
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, March 16, 2009, 12:59 AM











    
            dbrock178 wrote:

> Hello all,

> I am looking to create my first homemade pcb using the photolithlgraphy method. I've read some tutorials on both methods and did some browsing on the board here, but I still have some questions.

> 

> 1. Does negative dry film resist share the same characteristic of longer development times for aged film that pre-coated boards have?

> 

> 2. Does negative dry film resist provide greater detail than positive pre-coated boards?

> 

> 3. What are some advantages/disadvan tages of negative dry film vs positive pre-coated boards besides the following?

> 

> -Negative dry film: Lower cost

> -Negative dry film: Needs clean board/more steps required

> 



I've never used pre-coated positive photoresist boards so I cannot 

comment. Does anyone know how this resists is applied, since I don't 

think dry film positive resists exist. All the positive resists I've 

come across are in liquid solvent.



I've use the old spray on Electrolube PRP photoresist , and all I can 

say is its a pita to use compared to negative dry film. Even when you do 

manage to get a uniform, contaminate free, well adhering coating, the 

stuff is lot less forgiving in the developer and exposure time compared 

to negative dry film.



Professional PCB manufactures exclusively use negative dry film 

photoresist. It must be economical overall, weather that's because it is 

easier to process with simple equipment or lower bulk material cost.




 

      

    
    
	
	 
	
	








	


	
	


      

[Non-text portions of this message have been removed]

> I've never used pre-coated positive photoresist boards so I cannot 
> comment. Does anyone know how this resists is applied, since I don't 
> think dry film positive resists exist. All the positive resists I've 
> come across are in liquid solvent.
> 
> I've use the old spray on Electrolube PRP photoresist , and all I can 
> say is its a pita to use compared to negative dry film. Even when you do 
> manage to get a uniform, contaminate free, well adhering coating, the 
> stuff is lot less forgiving in the developer and exposure time compared 
> to negative dry film.
> 
> Professional PCB manufactures exclusively use negative dry film 
> photoresist. It must be economical overall, weather that's because it is 
> easier to process with simple equipment or lower bulk material cost.
>

I use the M G Chemicals 600 series boards normally the 630 8" x 12" this is positive resist.  I have had good results in using them.  One of my boards is pictured on the home page of this group.  Sorry I do not know off hand cost compared to doing neg. dry film.  I have been thinking about trying out the Neg. Dry Film resist.  M G Chemicals is now offering the Dry Film resist in small quantity, 5 ft x 12". Mouser carries it but does not seem to keep a lot of it in stock and list a 2 week lead time for it.  

I do not recommend trying to use the DIY positive resist liquid.  It can and does work but it is a real pain to use, I used it back some 17 years ago.

www.mouser.com is the best source that I have found for the M G Chemicals products.

Ben