Ted

I'm sure there will be a variety of responses to this one. We address
this issue as follows:

For our double sided designs: 

1) Tg 125C minimum. No other requirement relative to materials.

For our multilayer designs;

1) Tg 135C MINIMUM. Higher can be used - supplier's choice.

2) Where laminate Tg used is less than 200C AND overall thickness is
greater than or equal to .093", we require 1 mil minimum PTH copper.

3) For all other designs (i.e. thickness less than .093, Tg greater than
200C), minimum PTH copper thickness is .8 mils.

Some of our more assembly heat critical designs will also carry a
"plating taper less than or equal to 70%" specification. We define
plating taper as plating thickness at PTH knee to plating thickness at
PTH center.

The above are a result of extensive internal testing. Since our designs
tend to be somewhat unique, it might be of limited value to others.

Regards

Gerry

>----------
>From: 	Edwards, Ted A (AZ75)[SMTP:[log in to unmask]]
>Sent: 	Wednesday, February 19, 1997 3:11 PM
>To: 	[log in to unmask]
>Subject: 	DESIGN:  Aspect Ratio versus Material choice
>
>     We are redoing our specification and are wondering if anyone has design 
>guidelines that take into account either aspect ratio (or drilled hole size) 
>and choice of material into account.  For instance on a 0.125" board with a 
>0.0135" hole( ratio 9.4), or a 0.093" board with a 0.0135"  mil hole(ratio 
>6.9) do you specify to the designer use of a higher glass transition 
>material that you do on the same hole size on a 0.062"        ( ratio4.6)? 
> An example would be polyimide for the 0.125 thickness, multifunctional for 
>the 0.093 thickness and standard FR-4 for the 0.062 thickness or a chart 
>that shows increasing thickness or aspect ratio versus what material should 
>be used.  Anybody have any thoughts on this or comments?  Or is there any 
>fabrication industry consensus?
>          Thanks in advance for your inputs;
>               [log in to unmask]  
>
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