Hi Pete
Are you are buying your pre-sensitised board from Maplin? Particularly
from a store rather than mail-order? The only major problem I have had
has been with board bought from a Maplin store.
I normally buy board from Mega Electronics and was getting quite blase.
Exposure time (4 mins) always gave consistent good results. Then I
bought some Maplin board, exposed it in the same way, and had results
very similar to yours. I guess the stores don't sell much pre-sensitised
board and it may have been on the shelf for a long time?
I do still buy board from Maplin. There is a store just a few miles away
and so it is very convienient if I only need small quantities. But I
always run a test strip to determine the optimum exposure for each batch.
Regards
Paul
On Mon, Mar 5, 2012 at 12:45 AM, Pete <pete@...> wrote:
>> ∗∗
>>
>>
>> Hi,
>>
>> I am trying to etch a small PCB and finding it etches unevenly leaving a
>> small area of copper which is stubborn to remove. Just leaving in the
>> etchant for longer starts to undermine the tracks that etched ok.
>>
>> Here's what I do:
>>
>> 1. Print the track layout on inkjet printer using transparency film.
>>
>> 2. Lay the film ink side down onto a 3" x 2" single sided photo resist
>> coated copper clad board (cut from a Maplin Size 4 ref KU14)
>>
>> 3. Expose in a home made LED Light box for 4 minutes
>>
>> 4. Develop in Universal Developer (PBD2) Sodium Metasilicate for 1 minute.
>>
>> 5. Etch in Ferric Chloride track side down for 16 mins, agitating every
>> minute or so.
>>
>> The result is most of the copper dissolves after 10 mins then it leaves a
>> small area which refuses to disappear after waiting a further 5 minutes.
>>
>> A photo of the etched board is here
>>
>> https://picasaweb.google.com/109391378120539635298
>>
>> On close inspection of the board the unetched copper is left as stripes.
>> So I am wondering if this is a board problem or the process.
>>
>> Any help is appreciated.
>>
>> Thanks
>> Pete
>>
>>
>>
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