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. Jason. -----Original Message----- From: Anand Kulkarni [mailto:anand287@;lycos.com] Sent: 05 November 2002 22:47 To: PROTEL USER Group 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 OR 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 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * To post a message: mailto:proteledaforum@;techservinc.com * * To leave this list visit: * http://www.techservinc.com/protelusers/leave.html * * Contact the list manager: * mailto:ForumAdministrator@;TechServInc.com * * Forum Guidelines Rules: * http://www.techservinc.com/protelusers/forumrules.html * * Browse or Search previous postings: * http://www.mail-archive.com/proteledaforum@;techservinc.com * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
