In earlier days, the plastic covering of the chip was quite thick, and 
would provide
protection from fairly high external pressure. In other words, water 
pressure would have to be
very high to get through to the device inside.

But these very thin packages do not have the level of protection that 
thick packages have.
If you clean with water, you should bake the PCB to ensure the removal 
of any trapped water.
I consider TSSOP to fall into this catagory.

What I do is to clean with paint thinner first, then use hot soapy 
water, then clean water, then
a small 125F bakeout in the oven (make sure temp is reached then turn 
the oven off and let everything
slowly dry out and cool down at the same time). bakeout lasts for about 
1 hr.

If I believe moisture is going to be a problem, I will dipcoat the final 
PCB with an RTV coating.

F

Philip Stortz wrote:

>so what are people doing about chips that are "moisture sensitive" and
>what do the different levels mean (i.e. is "level 1" highly sensitive or
>no problem?).  i've sampled a number of such chips, and while i'm not
>too worried (wyoming is dry) i'd like to know, and i'd like to know if i
>really should bake these guys overnight to be safe, particularly on the
>larger ones.  (fyi, i solder a 28 pin dip faster and better than most,
>so i'm quick, but i'd hate to pop a chip).  i also may be using a
>home-brew oven eventually, which i suspect makes it more of an issue
>given the longer and greater heating that's likely (assuming i don't run
>into problems doing it by hand, which always has to start a mental timer
>before i over do things).
>
>"John J. McDonough" wrote:
>  
>
>>Mark
>>
>>Let me elaborate on this a bit.  I know it seems impossible and although
>>it's not hard, there are a lot of dots unconnected here.
>>
>>An 8 pin TSSOP is a piece of cake.  Nothing needs described other than don't
>>be afraid of it.  But the more interesting ones seem to be 28 pins or more.
>>These take a bit of thought.
>>
>>    
>>
>--------
>
>  
>


-- 
Note: Attachments must be sent to
 attach@engineer.cotse.net, and 
 MAY delay replies to this message.
        520-219-2363

_______________________________________________
http://www.piclist.com
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist