solder pin vs. press fit pin

[padmaster]

I'm trying to build a padstack that will accomadate both, a solderable pin (http://www.samtec.com/ftppub/pdf/TMM_TH.PDF) and a press fit pin (http://www.samtec.com/ftppub/cpdf/ptt-mkt.pdf) version of a connector.

What I have so far is:

pad size = external .055 - internal .050 - drill .033

On the fab dwg I'll put this note for those holes:

Initial drill: .036 +/- .001
finished hole: .031-.034



The board is 4 layers, 1 oz. nominal all layers, external layers plated up to 1.5 oz. then HASL.

Is sourcing solder pin parts and press fit pin parts common practice? Good idea? Bad idea?

Will this setup give me a reliable barrel for both pin versions?

[Skip Yutkus]

Padmaster,

I've been in the press-fit (backplane) industry for a long time, don't make the mistake that is made quite frequently, read the connector manufacturer's data sheet carefully, some will give you the recommended padsize, some won't but the most important detail is the drill size, (hole size before plating), and then the finished hole size, make sure you follow the specified dimensions and even go to the trouble of specifying the drill to be used on your fab drawing - believe it or not if the wrong drill is used and even if the PTH is in tolerance pressfit may not work all of the time.

Skip

[cadpro2k]

Hi Padman.

No, not a really good idea. Make up your mind, and go with press-fit. :) With the press-fit conns, the manufacturer normally will give you a drill callout and the finished hole callout (including tolerance). I see a problem with calling out a drill hole with 1 mil tolerance. Might be too tight. I'd say if you are calling out such tight tolerances, just go with press-fit.

I've always had lib parts for both conditions though. If you've got small holes for press-fit and try to plug in solderable pins, it could very well be too tight a fit, and manufacturing will yell!

Good day.

[Skip Yutkus]

Cadpro2k,

If the correct drill size is used then +/- 0.001", (sorry Tom!), should not be a problem on the hole before plating - some hole shrinkage occurs after drilling but never more than .001"

Skip

[Tom]

padmaster,

My take on the press-fit verses solder pin is that you cannot mix them and achieve optimal results. A press-fit pin needs a nice tight hole that the pin can barely fit in and has to be pressed in. If you try to solder this pin, the component lead must be small enough for solder to fit inside the hole too. A normal hole size for soldering pins is 0.3mm (.012") over the lead size. This allows for machine insertion tolerances but also allows some solder to go up inside the hole for a good connection.

[robert Tarzwell]

Your spec could get you into trouble.
The boards shop could drill a 35 and be in spec and finnish the hole a 34 leaving only 1/2 tmill of plating which is not enough.
make your finnished spec lower and tighter say 31-32 essuring a proper plate in the hole.
It is common when using push in pins to specify a very tight tolerance such as 32 +_ .0005 Push in pins need a tight fit to work with proper dimemtions and finnal fit I would suggest you cantact the pin manufacture and get the spec's
Robert Tarzwell

[padmaster]

Originally posted by Tom Hausherr
padmaster,

My take on the press-fit verses solder pin is that you cannot mix them and achieve optimal results. A press-fit pin needs a nice tight hole that the pin can barely fit in and has to be pressed in. If you try to solder this pin, the component lead must be small enough for solder to fit inside the hole too. A normal hole size for soldering pins is 0.3mm (.012") over the lead size. This allows for machine insertion tolerances but also allows some solder to go up inside the hole for a good connection.


This was basically my argument against sourcing press fit with solder pins. I don't believe you can mix the two and get reliable connections. Unfortunately, I must do what I'm told to do.

Seems to me manufacturers would make the pin dimensions close enough where you could use either pin configuration.

[Cadcrusher]

Press fit verses solder .... Another thing to consider is with press fit pin when you make a connection to a plane you shouldn't thermal relief the connection. With out thermal relief you will never be able to unsolder the pin with out delaminating your board.

[padmaster]

Originally posted by Cadcrusher
Press fit verses solder .... Another thing to consider is with press fit pin when you make a connection to a plane you shouldn't thermal relief the connection. With out thermal relief you will never be able to unsolder the pin with out delaminating your board.


Good point. I did use thermal reliefs.


The thing that worries me is that the press fit is the preffered source and will most likely be used most of the time. Considering I made the hole slightly larger than the mfg. spec, I'm concerned that the connectors may be pulled off the board.

[Cadcrusher]

A press fit pin can crack the barrel on a hole with thermal reliefs.

[Skip Yutkus]

Most solder versions of press-fit connectors are compatible with the press-fit hole size, I've only run into a couple that are not - what is the connector in question?

A direct plane connection is preffered for press-fit primarily because it lowers the inductance of the connection.

Skip

[padmaster]

Originally posted by Skip Yutkus
Most solder versions of press-fit connectors are compatible with the press-fit hole size, I've only run into a couple that are not - what is the connector in question?

A direct plane connection is preffered for press-fit primarily because it lowers the inductance of the connection.

Skip


Click on the links in my first post.

[Skip Yutkus]

It's going to be close - the pressfit finished hole diameter is specified as .031 +/- .003, (.028-.034), the diagonal of the solder pin is .028 - chances are if you go with the press-fit hole spec. the solder version would work, but it's possible to have an interference with the diagonal of the solder pin. If you tighten up the hole tolerance to +/- .002 you have a better chance of avoiding a problem - yes the PCB shop may scream, but they can do it.

Skip

[royl]

I agree with all of the above that the hole size is the most important aspect of "press-fit" technology. You can solder another connector in but I wouldn't want to remove it. Especially if the tails are even remotely close to the size of the press-fit pins.
Destruction is almost certainly guaranteed. Best bet....go with press fit only. You can used sollid connections on your plane connections too.