Reflowing a module

Thread Starter

MrSoftware

Joined Oct 29, 2013
1,974
Can anyone offer tips on reflowing a module onto a board? The challenge I'm expecting is that to get the module hot enough to flow the solder under it, the solder on every part on the module itself (under the metal shield) is also going to be molten, so any little bump will scoot the shield over (it's floating too) and scramble all the little 0402's under there. Other than pre-heating the area with air before floating the module on, has anyone else done this before? Am I better putting the entire board in an oven and reflowing everything?

Basically I fat fingered some wires and popped the module; the board is $60 and a module is $10, so I bought a couple modules. Getting the dead one off, the old module definitely got hot enough that everything under the shield was floating, and when I slipped with the tweezers and touched the shield, it moved very easily, so that's the part I'm sweating.


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cmartinez

Joined Jan 17, 2007
7,243
Can anyone offer tips on reflowing a module onto a board? The challenge I'm expecting is that to get the module hot enough to flow the solder under it, the solder on every part on the module itself (under the metal shield) is also going to be molten, so any little bump will scoot the shield over (it's floating too) and scramble all the little 0402's under there. Other than pre-heating the area with air before floating the module on, has anyone else done this before? Am I better putting the entire board in an oven and reflowing everything?

Basically I fat fingered some wires and popped the module; the board is $60 and a module is $10, so I bought a couple modules. Getting the dead one off, the old module definitely got hot enough that everything under the shield was floating, and when I slipped with the tweezers and touched the shield, it moved very easily, so that's the part I'm sweating.


View attachment 164909

View attachment 164910
Wow ... it's a challenge alright ... Ideally, I'd only heat the part of the circuit to which the module is attached, and not the entire thing. Although that could create stresses that might or might not affect the rest of the circuitry. I'd consider placing the module in an oven, and heat the part on the PCB to which it will be attached using a hot air reflow station. But maybe it would be close to impossible to manually maneuver the module into place.
 

dl324

Joined Mar 30, 2015
12,462
Without some professional equipment and a stencil, it's going to be difficult to get the right amount of solder on the pads, the correct amount of heat, and you won't be able to check for bad solder joints. Hidden pads aren't really a DIY job.
 

Thread Starter

MrSoftware

Joined Oct 29, 2013
1,974
A stencil would definitely help, but wasn't in the budget at this point. Instead of paste, I'm thinking of cleaning all the pads then tinning them, flooding the area with no-clean flux, preheat both the board and module with air then either (a) try to float it on with hot air, or (b) put it in the pre-heated oven and hope that the pre-heated areas of the PCB flow before the rest of the board gets hot enough to cause any problems. I just don't know how long it will take for the solder under the module to melt.. I'm leaning towards the oven method but definitely open to suggestions.
 

kubeek

Joined Sep 20, 2005
5,744
A stencil would definitely help, but wasn't in the budget at this point. Instead of paste, I'm thinking of cleaning all the pads then tinning them, flooding the area with no-clean flux, preheat both the board and module with air then either (a) try to float it on with hot air, or (b) put it in the pre-heated oven and hope...
If stencil is not an option, and it would be hard to even get it in place to do just that component, then I would go with solution A. Lots of flux, even but rather small amount of solder on the board pads, preheat the whole board to a high temperatrue of say 120-150°C and then very hot air with low flow to bump the module above the melting temperature. Possibly hot air from both sides on the area of the part, if there are no parts on the bottom that could fall off.
 

Thread Starter

MrSoftware

Joined Oct 29, 2013
1,974
It works! Right or wrong, here's what I did; First I flooded the PCB footprint with flux and cleaned the lead-free solder off of the pads. Then I swabbed it clean with denatured alcohol, flooded it with flux then rolled a ball of leaded solder around the pads with the iron to tin them (technique from one of the videos above). See the picture below of the footprint tinned and the new module void of any solder. Next pre-heat the footprint and module with air, but not hot enough to melt anything, and keeping the footprint flooded with flux. Then place the module and carefully put the whole board into a pre-heated 400F convection oven (toaster oven with a fan, dedicated to reflowing). I put a tiny piece of solder on the PCB next to the module to get some idea of when the PCB started getting hot. It took about 2.5 minutes for the PCB to look like it was floating, and I opened the oven door to let it start cooling after about 3 minutes. Cooled it off, plugged it in and presto it works!!

Pads tinned, next to new module:
upload_2018-12-4_15-39-4.png


New module mounted:

upload_2018-12-4_15-40-40.png

Stuff under the module shield next to my finger for scale. Did not want to dislodge any of that stuff trying to float it on by hand with air!
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ian field

Joined Oct 27, 2012
6,539
Can anyone offer tips on reflowing a module onto a board? The challenge I'm expecting is that to get the module hot enough to flow the solder under it, the solder on every part on the module itself (under the metal shield) is also going to be molten, so any little bump will scoot the shield over (it's floating too) and scramble all the little 0402's under there. Other than pre-heating the area with air before floating the module on, has anyone else done this before? Am I better putting the entire board in an oven and reflowing everything?

Basically I fat fingered some wires and popped the module; the board is $60 and a module is $10, so I bought a couple modules. Getting the dead one off, the old module definitely got hot enough that everything under the shield was floating, and when I slipped with the tweezers and touched the shield, it moved very easily, so that's the part I'm sweating.


View attachment 164909

View attachment 164910
For whicheve home computer it was with the "red ring of death" - a bunch of guys installed reflow kit in a van and toured the country fixing them.

I'd probably dig out my finest tip iron, roll my sleeves up and put more coffee on.
 
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