How to rework Eggtimer TRS board?

[Kelly]

I have an RF module that I think is bad on an eggtimer TRS board. I have a replacement module from Cris. Any ideas on how to get the old board off? It's the module in the bottom left of the photo- 7 pads on one side, two on the opposite side. I don't have a rework station (but, could consider buying one if it's cheaper than a new TRS). I don't have a reflow oven, either. Could I just pop this in the kitchen oven and pull the board off when the solder melts? Any other ideas?

 

[heada]

Good solder wick and a flux pen and hope you didn't get any solder under the castilations (like you wanted to do when you first assembled it)

Before the kitchen oven, I'd go to goodwill and get a toaster oven.

 

[OverTheTop]

You could use a Dremel (or similar) and mechanically very carefully remove the board, then clean up the solder pads. Messy but doable. Not how I would do it (I have full rework facilities at work) but it depends on your skillset and tools available. The main thing to keep in mind is to not damage the main board or components.

Maybe you can use a hot air gun and protect the rest of the PCA from heat. Ordinary masking tape works quite well in this regard. You would have to go in gently, and a small nozzle on the hot air gun would improve the situation.

 

[Kelly]

You would have to go in gently, and a small nozzle on the hot air gun would improve the situation.

Thanks, but how does this work? Do I just pan the nozzle back and forth across the row of 7, and when the solder flows gently pry that side of the board up, and hope the other side doesn't peel any pads? As Aaron implied, I probably DO have solder under the board. I'm actually pretty decent at soldering, and have desoldered plenty of through-hole stuff, but never anything like this.

 

[Kelly]

I should add, I've seen reflow tools that direct the airflow along two rows, so that you can remove an entire SMT chip, but nothing that would fit both sides of this board simultaneously.

 

[OverTheTop]

Thanks, but how does this work? Do I just pan the nozzle back and forth across the row of 7, and when the solder flows gently pry that side of the board up, and hope the other side doesn't peel any pads?

You would need to heat it evenly across the RF board, as the two joints for the antenna complicate things. You would need to drive sufficient heat into it to melt all the joints at once.

 

[Voyager1]

What is the RF board not doing that suggests that it’s the problem? Does the rest of the board behave as expected? Does the altimeter side of the board function correctly?

If the RF module does need to be replaced, then I would probably use a combination of what heada and OTT have suggested. Carefully remove as much of the solder with wick and a flux pen, followed by carefully cutting through the half moon solder cups along the two edges. Once the RF board is removed, you can then clean up the solder pads. You do not want to damage or lift the solder pads on the main board, so don’t over heat them.

Fortunately, I have a rework station, so I wouldn’t use this method.

 

[n27sb]

I have done it successfully on a mini twice and re used them.
Remove as much solder with wick as you can from the two contacts near the antenna.
GENTLY slid the blade from a snap razor under the board as you re heat the two contacts.
The solder will not want to stick to the blade so use it as a shim between the contacts and the main board.
Don't get carried away and lift the board just yet.
Start heating the contacts on the other side by sliding your iron back and forth.
Try to keep the heat on top of the RF board. If it gets too hot we are trashing it, right.
You should still have your blade under the two far contacts. Pry GENTLY to lift that end of the board.
If you over do it you will lift the copper pads on the main board. If you get things too hot you will damage the main board.

Or send it to someone that reworks boards.

Good luck

 

[cerving]

You definitely want to remove as much solder as possible first. My experience has been that because of the size of the pads and their distance, a hot air rework tool isn't as effective as you might hope. The Chip Quik rework solder/flux works surprisingly well, however as Voyager1 mentioned you have to be very careful not to lift any pads.

 

[dvdsnyd]

Just to reiterate what others have said, the biggest thing to be careful of is lifting pads, which is caused by excess heat, as well as prying on components when they aren't loosened up enough.

 

[Landru]

My go-to when proper rework tools aren't available is a giant blob of solder.

Melt a huge ball of solder all along both sides of the pads. With a large blob, there will be just enough thermal mass to keep both sides molten at once if you keep switching sides with the iron. You can then either push the board off or lift and tap the whole pcb and it will fall right off.

You do need to be careful not to completely toast the pads, but a temp controlled iron should keep things relatively safe.

I've done this at least a few hundred times successfully.

 

[cerving]

That's basically what the Chip Quik solder does, except it melts at a very low temperature.

 

[SparkyVT]

My go-to when proper rework tools aren't available is a giant blob of solder.

That's how I do it. Big blob of solder that covers all the pads. They all melt at the same time and I can pop off the offending chip.

 

[OverTheTop]

My go-to when proper rework tools aren't available is a giant blob of solder.

That can work well too, although the length of the line of pads complicates matters a little here.

 

[Landru]

This video shows how to do it:

 

[Kelly]

By ChipQuik, you mean something like this?
https://smile.amazon.com/ChipQuik-SMD1-Leaded-Temperature-Removal/dp/B0019UZP7IThey make a lot of products, so I'm thinking you guys are talking about this low temp solder?
(I've tried running the iron back and forth over the pads - as I've done many times for removing DIP through-hole IC's - but no luck. Maybe this low-temp solder is what I need, I had never heard of it!)

So the process might be:
Remove as much solder as possible from all pads
use a razor blade to separate the antenna side, as Steve suggests
put a boatload of ChipQuik solder on the 7-pad side, and try to get all pads flowing with the iron.
(or, skip the razor and just try to blob-of-solder both sides)

I do have an adjustable iron, so that helps a bit.
Thanks, this gives me some better techniques to try.

 

[Kelly]

What is the RF board not doing that suggests that it’s the problem? Does the rest of the board behave as expected? Does the altimeter side of the board function correctly?

I had the board working fine - all functions - and then after a ground test (used the radio link to test fire a drogue and main on the ground) it stopped working. Hooking up to serial shows that the MP and GPS are working fine, but I can't make radio contact. Also, the blinkenlights on the RF module, which I think used to flash at 1hz when the board was synced with receiver, don't flash anymore. I verified there's power getting to the RF module, so the only thing I can think of to try next is to replace it. Other suggestions welcome.

 

[cerving]

By ChipQuik, you mean something like this?
https://smile.amazon.com/ChipQuik-SMD1-Leaded-Temperature-Removal/dp/B0019UZP7IThey make a lot of products, so I'm thinking you guys are talking about this low temp solder?
(I've tried running the iron back and forth over the pads - as I've done many times for removing DIP through-hole IC's - but no luck. Maybe this low-temp solder is what I need, I had never heard of it!)

So the process might be:
Remove as much solder as possible from all pads
use a razor blade to separate the antenna side, as Steve suggests
put a boatload of ChipQuik solder on the 7-pad side, and try to get all pads flowing with the iron.
(or, skip the razor and just try to blob-of-solder both sides)

I do have an adjustable iron, so that helps a bit.
Thanks, this gives me some better techniques to try.

Yes, the Chip Quik product is a very low temperature solder so it's much less likely to lift pads than using "regular" solder. It works great on SOIC-8 chips, OK on SOIC-14 chips, and not as well on larger chips like the SOIC-28 interface chip on the Proton. You will find that it is a challenge to keep the Chip Quik molten across all seven of those pads.

 

[AllDigital]

I've done a LOT of desoldering to save and reuse boards and components. More than I'd like to admit. I have bought a dozen different solutions, including pumps, wick, low temp solder, etc. If there are not many pins I can usually manage with just using the iron and wriggling the board free. But with more than 4-5 pins or a complicated job, my "go to" solution is still an old fashion desoldering iron -- right out of the 1984 catalog at Radio Shack. It isn't temp controlled, so you need to be careful, but there is something very satisfying about sucking up solder and spitting it out. Here is a cheap version of what I use (even cheaper ones available):

https://www.amazon.com/ECG-J-045-DS...words=desoldering+iron&qid=1616646336&sr=8-12

 

[Brian H.]

My go-to when proper rework tools aren't available is a giant blob of solder.

Melt a huge ball of solder all along both sides of the pads. With a large blob, there will be just enough thermal mass to keep both sides molten at once if you keep switching sides with the iron. You can then either push the board off or lift and tap the whole pcb and it will fall right off.

You do need to be careful not to completely toast the pads, but a temp controlled iron should keep things relatively safe.

I've done this at least a few hundred times successfully.

I have found this to be a very reliable method, been using it for many years. The key is keeping the iron moving quickly enough between all contacts to get all of them melted at once. Full solder bridging between pins on each side if possible. Temp controlled iron really helps to prevent board damage. Then remove excess solder with wick.

I have also used a toaster oven for re-flow work (dedicated strictly for electronics/lead contact), but doesn't work that well for removing individual components.

If you do a lot of electronics work, it is well worth it to invest in a workstation that has hot air re-flow tooling. I picked up one of the cheap chinese models from fleabay for about $65 and it is holding up well for hobby use.

 

[DaHabes]

Could I just pop this in the kitchen oven and pull the board off when the solder melts?

All of the solder would melt, the entire board would be destroyed.

 

[Kelly]

Wow, I got some of that low-temp solder, blobbed it on, and that RF board was off in a minute or two. Two more minutes and the replacement board was back on, and my Eggfinder works again. Thanks for the recommendations!

 

[cerving]

Yeah, that Chip Quik desoldering stuff is magic, at least for SOIC-8 and SOIC-14 chips. I haven't had to use it yet to desolder an RF module... fortunately.

 

[Kelly]

You said above that it would be 'challenging' to keep the chip quik molten, actually it was quite easy - magic, as you say. Just had to go over it a few times, as the video posted by Landru shows.

As always, thanks for the great service!