Ask the Experts
May 15, 2020
How To Rework SMT Connector with Center Ground Strip
I need to remove a SMT connector that has a ground strip down the middle. Can you give me some tips on how to remove it and put a new one on an assembled PCB?
Expert Panel Responses
We perform this type of repair on a regular basis. There are several important variables to be considered prior to establishing your approach and the equipment we use is a bit more sophisticated than a soldering iron and wick. We would approach this rework similar to a BGA device removal and replacement.
As such, we use temperature controlled "Hot Gas" printed circuit board rework equipment. This equipment applies precisely controlled top and bottom heat via resistance heat plates from the bottom and a hot gas blower from the top down. We have had great success over the years using this equipment for this application, use of that type of equipment would be highly recommended.
Beyond the equipment recommendation there are several very important variables to be considered prior to jumping into the repair/rework, this would be my list:
Finally I offer this tip:
- How big is the connector? Connector Size and shape will dictate how much and where you apply the heat.
- What are the solder chemistries? Lead free solders will require more heat than leaded solder.
- What is the connector housing made of... can it withstand the solder reflow temperatures? Fortunately most SMT connectors are designed for handling solder reflow temperatures but check to be sure.
- How much room do you have around the target connector?
- Are there heat sensitive components close to the target connector? You may need to protect those components from collateral heat damage during the rework process.
- Do you need to bake moisture out of the printed circuit assembly prior to the repair/rework step? It may be just an insurance policy but it's better than delamination caused by moisture.
If the board construction allows (mainly no heat sensitive components on the bottom side of the PCB directly under the connector) we try to drive heat from the bottom up through the PCB. This will facilitate the reflow of the solder connecting the center ground strip. This also eliminates the need to drive to much heat from the top down through the connector and potentially damaging the plastic connector housing.
I hope this helps, best of luck with all of your future rework and repair applications.
Circuit Technology Center
Mr. Vigneau has been a key member of the team at Circuit Technology Center since 2008. He has vast expertise, experience and understanding of complex circuit board rework, repair and modification operations. He is one of the most knowledgeable experts in this area across the globe.
I'd recommend that you use a hot-air wand to remove, assuming you don't have to salvage the connector, making sure you use flux during this process. Clean your SMT lands so that they are as smooth and level as you can get them. Now, if the ground pad was for electrical purposes, then you'll want to apply solder paste (no clean) only to the ground pad, I'd recommend a thin layer that covers no more than 50-60% of the pad.
This should keep the connector flat when it reflows. Ultimately, it would be best to re-reflow this through an oven, but I suspect that the rest of the assembly can't tolerate that. So, reflowing it again with the hot air wand would be the best way to go about it. That would best be accomplished using a pre-heating station as well, provided that the temp stays a little below the flux activation temperature.
Once the ground pad reflows, you can hand solder the connector pins. If the soldered ground strip is only there for mechanical support, I'd recommend not soldering it. I'd place the connector and solder the connection pins by hand, then using a good epoxy, glue the connector in place. This will make it much more difficult to repair in the future, so keep that in mind. Good luck!
Esterline Interface Technologies
Mr. Hughes has been in the electronics manufacturing field for 20 years. Operating the processes and as a manufacturing engineer for the last 14 years. He is also a CIT as well as an SMTA Certified Process Engineer.
Normally we remove these using a hot-air rework station. If the board is high-mass (very thick), pre-heating the board to about 70 degrees C can help ease removal. It may be necessary to procure an appropriate nozzle in order to heat the entire length of the connector uniformly.
After removal, remove excess solder from the lands, re-apply paste with a mini-stencil, and place the connector manually, then reflow using the hot air rework station.
If there are nearby components that you do not want to be reflowed, create a heat guard from a piece of aluminum foil with a cut-out the size of the connector. Press the foil down to the board surface to limit the amount of air that penetrates underneath.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Reworking the connector you describe is similar to reworking an array device. I would recommend hot air as the heating method, using an open baffled nozzle that will cover the entire connector. It is important to heat the entire connector evenly.
Your replacement connector should have a plastic clip-on or Kapton tape dot to provide a surface for vacuum pick-up. Tweezers can be used for removal but may be a bit more difficult. After removal the solder pads will need to be cleaned/ wicked flat and new solder paste applied with a mini-stencil. After placing the new connector you will just repeat the same reflow profile for re-attachment.
If you don't have access to a hot air rework station and just need to remove it you can use a hand soldering iron. The first step would be to lift all of the pins off the solder pads. Then you will need to clip/ cut the body of the connector in order to expose the center strip. After exposing you should be able to get the iron on the solder joints and remove, they typically have multiple strips so you just de-solder one at a time. Extreme caution must be taken to make sure you do not pull any pads off the board.
Process Sciences, Inc.
Stephen Schoppe is President of Process Sciences, Inc., and has 19 years experience providing SMT services to electronics manufacturers. Stephen provides consulting to several Fortune 500 clients on solder and SMT processes, and is a frequent guest speaker at SMT industry events.