CCD-world: PC board CCD carriers

[David Ouellette]

The following was posted to CCD-world:


My understanding is that FR-4 differs from G-10 in the flammability.  FR-4
has bromine added to extinguish flame once the source of ignition is
removed, and thus is popular in consumer electronics.  Mechanical
properties, dissipation factor, etc. are the same as G-10(see IPC-D-330 for
more info).  The resins used to stack-up the layers might vary from
fabricator to fabricator, so generally once I've found someone whose product
is acceptable I stick with them.  Lowest prices aren't always best...

I agree with the observation that solder mask layers should be avoided.  I
also avoid silk-screened graphics unless absolutely necessary.  I have not
seen any problems relating to vias in my boards, though I have always made
them as small as practical to minimize expansion/contraction problems.

As for gold, I suggest great caution if you are going to wirebond to the
traces.  Most of the gold you see on circuit cards, for example on edge
fingers, is "hard" gold which contains cobalt for greater wear resistance.
This is incredibly difficult to wirebond to.  Be sure your supplier will be
able to provide you with electrolytic wirebondable gold per MIL-G-45204C
Type III grade A (min. purity 99.998%, less than 90 Knoop hardness).
Luckily, with the increase of MCM-L products (Multi-Chip-Module Laminate
technology), there is an increasing number of suppliers.  The new
(relatively) Palladium finishes are supposed to be good.  In any event,
support the board well during wirebonding.  Using a high frequency bonder
may also be helpful.

Dave

David Ouellette
Steward Observatory
CCD Laboratory
933 N. Cherry Avenue
Tucson, AZ  82721-0065

Phone:  520-621-5228
Fax:    520-626-4330
http://sauron.as.arizona.edu/


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