This is a question for your production process and/or house.

If you use through hole, it could mean adding an otherwise un-required wave,
machine or hand
soldering process to produce the PCA.  If you are producing a number of
boards, this can
be costly.

If you have components on the top and the bottom, you'll have to use
selective wave, this is
even more costly and time consuming.

The alternative for a PTH part is PIH 'paste in hole'. Using this method you
can reflow the whole
board in one pass, trouble is, you nee to use more costly high-temperature
plastics on the
connectors, this also makes them less available.

If your board contains a lot of other PTH parts that you can't avoid, then
go for the PTH connector, I've
found it will usually be cheaper. Remember you can't usually wave solder the
bottom side if
you have components on it.

As for the pad to track entry just put a via close to the pin, optimise the
via and pad size to allow
the vias to be in-between the pads,  if you are using multi-layer you'll be
surprised how little 
annular ring you need.  The same is true for PTH and SMT.  Don't forget to
tent vias that you can't see, or
that are close together, especially if it will go through a wave. Failing to
do so can get you a lot of solder shorts.

Assuming you are not at incredibly high frequencies, the difference between
a terminating resistor
connected to a via connected to an internal track, and the same track just
on the top or bottom only
comes down to the impedance of the track. This, in turn is mostly governed
by the plane construction.
The additional vias and pads etc make little difference within the rest of
the uncertainties if the stubs are kept short.

Keep source termination as close as possible to the source, otherwise put
the termination as close as possible to the end of the line.


-----Original Message-----
From: Anand Kulkarni [mailto:anand287@;]
Sent: 05 November 2002 22:47
Subject: [PEDA] general question about connectors : thru-hole versus
surface mount

 Hi all,

my question is not protel specific but it still has to do with pcb 
so i'll go ahead and ask it here.I hope it is alright .

my problem is as follows :

I have  to choose between using 

1)  68 pin SCSI surface mount female connector  
2)  68 pin  SCSI  thru hole female  connector.

This connector ((( actually there are 16 of the same connector repeated 
on the board ))) has traces  going from its pins ((( pads for surface 
mount if I choose that )))  to  the I/O pins of a ball-grid-array FPGA part.

These traces would be routed on various signal layers .

Now if I choose the thru-hole connector then the traces can directly 
attach to the connector pins in whichever layer it is routed ((( 
since the connector pins will go thru all possible layers )))  ; 
on the other hand if I choose the surface mount connector I will 
need every trace to be brought up to the top signal layer so that 
they may attach to the surface mount connector pad.

Am I right ?

Further in case I choose the thru-hole connector and I need to use 
a terminating resistor , what do I have to do ? 
Since the trace going from the connector to the FPGA is entirely 
 contained in one of the internal signal layers ((( and the terminating 
resistor must be placed somewhere in between the FPGA I/O pin and 
the connector pin ))) , where can I put the terminating resistor ?  

What is generally done in such a situation ?

please do reply with your suggestions,

thanks very much

Anand Kulkarni

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