Thanks Brian and yes the technology 25 years ago worked well with this general approach but with the use of QFNs, and 0201s and smaller components with selective, hand soldering and touch up soldering leaving pockets of flux causing failures on very sensitive circuits but still passing the ROSE test with less than 0.25 ug/in2 eq NaCl there has to be a better way of looking at one componet area that fails instead of 2-20 liters of IPA/DI water flooding and resistivity. In comparison todays soldermask porosity can be very porous and trap moisture from the cleaning and not removed by any type of blow off. Baking is still the best option for remove moisture but has no bearing on the level of contamination below a single component.
In a message dated 01/09/12 11:33:59 Eastern Standard Time, [log in to unmask] writes:
In a way, this thread amuses me. It largely goes through two of the
arguments I put forward in a book I wrote over 25 years ago. Those who
have a copy may care to have a look at section 17.6 Water quality (pp
204-211) and section 17.9.2.7 (p.293) Drying which discusses the
air-knifing and thermal drying. I think I was possibly the first to
propose air knifing (which is not the same as blowing with compressed
air) as a means of reducing the residual contamination and I even had an
efficient batch machine developed for this (section 17.9.1.2.2 (pp
224-225). We did weighing tests with this machine, as well as ionic
contamination tests, and found that, on an average, the air knife phase
removed about 90-95% of the residual water, the blown hot air phase
evaporated nearly all the remainder. With our tap water, which had a
typical conductivity of 380 µS-cm, an assembly dipped into the water
came out of the machine with an ionic contamination of <1 µg/cm² eq.
NaCl and with DI water <0.1 µg/cm² eq. NaCl. However, remember that
those were the days of through-hole components! Notwithstanding, we had
many satisfied customers who used these machines with SM components and
who did regular ionic contamination tests and still obtained good
results. The secret was the fact that the air knives were rotary and
therefore the blast had a very variable angle of attack on the boards.
If anyone wants to know more, please contact me off-line.
Brian
On 08/01/2012 01:36, Gary Bremer wrote:
> I am presently working as an contractor for the next few months then back to unemployment, last place I worked was Jet Propulsion Laboratory on the Mars Science Laboratory. These are lighted panels for various aircraft and the company policy is for J-STD-001/IPC-A-610 Class 3 The failure is with miniature T-1 lamps that stop working after going through an baking process. Other boards that use these lamps but use RMA flux do not have this problem, I suspect the cleaning process and the flux. They do not check ionic contamination and handle the boards with bare hands and the operators even know when components are ESD sensitive or not. I have recommended they change the cleaning process to an Aqueous type batch cleaner but this cost money which they do not wish to spend. Their process person believes that their process is fine and something else is causing the problem (bad lamps, forming lamp leads, etc.). This goes against all my knowledge and training.
>
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