In answer to:   David Bergman
                      Jon Holmen
                      Mike Cussen
                      Jerry Cupples

When reading the notes by the above, I felt it necessary to respond.  
David Berman's response includes mostly the bare board process of 
baking, with some pre-assembly baking requirements.  
I must respond to to some of the comments and also give an opinion.

First, why do people bake boards prior to assembly?  Baking may may, 
or may not, help solder joint pinholes, depending if there are 
plating voids present.  Solder joint blow holes are almost always 
caused by a wetting problem with the board or components.  Therefore, 
baking is a waste of time for these reasons.  Further, there is 
nothing that will diminish solderability faster than a bake cycle of 
the boards prior to soldering.  

Some people will bake boards to help prevent delamination.  However, 
when is the last time you saw either measles or delamination?  Not 
very often, that's for sure.  The process of board manufacture, in 
parallel with bare board materials has improved significantly over 
the years.  Then why a bake cycle prior to a soldering process.  
Because of the statement Jerry Cupples made!  If the boards 
delaminate, without first seeing a bake cycle, send them bake to the 
vendor and make him eat the components also.  He said they won't 
quibble.

Let's look at that statement.  You chose the material to use, not 
your vendor.  You could have used a more expensive polyimide material 
and added another 30% to the price of your boards.  Though it's not 
an industry practice to eat the cost of components, your vendor may 
possibly eat this cost.  However, this solely depends on how good of 
a customer you are, the total value of the loss and if they choose to 
continue doing business with you.  Many cases have been lost in court 
on the subject.

Why should a vendor eat this cost?  You have a QC department to 
ensure that there will be no delamination.  You chose the materials.  
The process to manufacture boards varies very little from one vendor 
to another.  Why should the vendor eat the cost of the components?  
They shouldn't!  They are only responsible to replace the cost of the 
bare board.....Period.  Therefore, when a vendor asked you how and 
when you baked your boards, you must tell them.  When a vendor 
insists that you bake your boards prior to a soldering process, then 
it is a must.  Though delamination is not much of a problem today, it 
is imperative to follow the vendors instructions or all resulting 
quality issues must be your sole responsibility.

Though I do not like any type of bake cycle for solderability issues, 
and further don't think that it is necessary, you must include baking 
if it is a vendor requirement.  The higher your layer count, the more 
expensive the board and the more necessary baking becomes.  All 
baking must be accomplished within 3 to 4 hours just prior to any 
soldering process.  Though it is difficult to remove all moisture 
from your multi layer boards, a 250 degree "F" bake for 3 to 4 hours 
will remove most of the moisture, thus, reducing the possiblility of 
delamination.  Some people bake all of their boards overnight.  The 
longer you bake, the more you lose solderability.  Everyone seems to 
have a different criteria.  People with extended bake cycles must 
accept all non-solderable conditions as part of their process.  To 
this I must say good luck!

I would be happy to discuss this on the phone with anyone interested.


Norm Einarson
PRINTED CIRCUIT TECHNOLOGY
Tel:  (617) 938-1440