Alessio
The high impedance present due to electroless tin manifested itsself on a sample and hold 14 bit A to D circuit and associated amplifier. Six boards had excessive errors whilst two worked perfectly. The two working boards were not electroless tin plated. The effect of the tin caused the sample and hold capaicitor DC value to droop during the A-D conversion. It could not be measured with a multimeter. The associatd DC amplifier had incorret gain, The leakage across the gain setting resistor was sufficient to cause errors. All the boards had been cleaned in Arklone to remove flux residues.
Malcolm
I don't suffer from insanity I enjoy it!
--- On Mon, 9/13/10, Alessio Sangalli <alesan@...> wrote:
From: Alessio Sangalli <alesan@...>
Subject: Re: [Homebrew_PCBs] Re: Again on tinning!
To: Homebrew_PCBs@yahoogroups.com
Date: Monday, September 13, 2010, 5:04 AM
On 09/12/2010 11:36 AM, Malcolm Parker-Lisberg wrote:
> It does deposit tin on the FR4 surface, and will prove problematic if you have high impedance circuits, it also causes problems when the board is conformally coated, with tin migration under the coating.
> Conformally coating the board first and then applying the tin is a better solution for high impedace or low leakage PCB requirements.
> It should not be a roblem with normal home PCB CMOS circuits.
Do you have more data on this? This is chemistry, I am not qualified to
understand the process for which the tin may deposit on the board, but:
- is this measurable?
- how much it changes a board? Can one see it with a multimeter?
- do you have any kind of number or data?
bye
as
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