We are SMT soldering a through-hole PC 104 connector. We have tried preforms and are unable to get all of the pins soldered. Phil Zarrow and Jim Hall, The Assembly Brothers, share their own suggestions in this scenario. Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis.
He has vast experience in SMT equipment, materials and processes.
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics.
He is a pioneer in the science of reflow.
And welcome to Board Talk with Phil Zarrow and Jim Hall, The Assembly Brothers, otherwise working their day jobs as ITM Consulting. But here to answer your questions on process, materials, equipment and other electronic assembly related topics.
Today Jim, we have an interesting question from P.D. He or she asks, what are your recommendations for SMT soldering a through-hole PC 104 connector? We have tried several methods, including preforms, and are unable to get all of the pins soldered. This brings up a few issues.
First of all, I am going to make the assumption because you say SMT soldering a through-hole connector and the fact that you mentioned pre-forms that you are using intrusive soldering or pin in paste methodology here. That is the first thing. I would say from a paste volume standpoint, obviously you want to make sure that your hole geometries are correct relative to the pin.
If you go to our web site, we have done work in the past on it and we have some formulas for intrusive soldering or reflow of through-hole, pin-in-paste, whatever you want to call it. Take a look at that. Our friend, Bob Willis, has also done work on this First of all, make sure your hole geometries are compatible with the thickness of the pin. Speaking of which, Jim PC 104 these are pretty hefty pins aren’t they?
Well, it is a general specification for interconnecting daughter boards and mother boards and your desktop PCs. There is actually a wide range of these connectors and some of them can be pretty massive. With a soldering problem, of course you ask are your surfaces solderable? Are the through-holes solderable? Are the pins solderable?
Do you have the proper amount of flux available and are you getting to the right temperature? My guess would be non-uniform temperatures.
That it is a larger connector and not all the pins are reaching full wetting temperatures. When you have a large connector, you have to put maybe a couple of thermocouples on it when you are profiling your reflow oven. Make sure that all of those pins, particularly in the middle, are reaching full wetting temperature in the barrels of the holes or else the solder isn’t going there.
If you have gone to pre-forms, then your pre-forms should give you the exact amount of solder and flux to give you a good solder joint. If you are not getting it with pre-forms, my feeling is it is probably a lack of heating on some of the pins because of thermal uniformity issue.
I think our consensus between my brother and I is that thermal uniformity, ample contribution there as well as solder volume, getting the right solder volume down there you need it too. Also, watch out for lead protrusion because you don’t want to be displacing some of that solder paste in to your oven. We generally recommend something like a 30 mil lead protrusion, as a maximum.
Thank you for listening to Board Talk. I just want to remind you that when you are soldering those pins, those good old PC 104 connector pins, don’t solder them like my brother.
Don’t solder like my brother.
I don't see any mention of flux, just solder preforms. Are the preforms fluxed - and is there enough. The only flux that matters is on the preform side next to the board and walls of the preform hole. The flux on top won't flow into the barrel, so doesn't help wetting.
Jim Smith, Electronics Manufacturing Sciences, Inc.
It wasn't mentioned how many layers in board or which pins were not up to spec. My thoughts were ground or voltage plans within inner layer. IPC spec is 50% of barrel for ground planes (good wetting on solder side) as they act like heat sinks.