Double Sided PCB SMT Soldering

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teqdruid
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Double Sided PCB SMT Soldering

Post by teqdruid » Wed Nov 08, 2006 2:20 pm

Thanks for the tutorials on SMT soldering SFE!

A current design I'm working on requires that surface mount components be mounted on both sides of a PCB... Any ideas on how to solder them?

If I bought a hot air rework gun, would it heat the board enough that components on one side would fall off when working on the other side?

I've also seen solder paste available that melts at different temperatures. The low temperature ones seem to melt around 183 C, and the next grade up melts at 218 C, but that's 424 F, and the skillet I've got only goes up to 420F, according to the label. My toaster oven will supposedly go up to 500F, but I don't have much confidence in that.

Any thoughts?

~John

riden
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Post by riden » Wed Nov 08, 2006 7:57 pm

I am an amateur when it comes to board fabrication, and I'm sure others with far more experience will chime in. I haven't done a lot of two-sided SMT assembly, but I have successfully reflowed two boards with components on both sides, and many more with components on one side. I use a reflow technique where I preheat the board using a coffee mug warmer. My Salton mug warmer gets the board up to around 200-220 degrees F, after which I use my hot air gun to finish the job.

For the two-sided boards, I selected one side (the one with the smallest/lightest components -- i.e. not the side with the SMT crystal, regulator, and power amp), placed the components, and used the technique described above. After letting the board cool somewhat, I placed the components on the other side, and used the hot air gun to reflow that side. In my limited experience, the smaller components tended to remain in place due to surface tension. My first attempt was doing the side with the heavier components first, and the regulator fell off when I did the other side!

BTW, high quality solder-wick is your friend! :)

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leon_heller
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Post by leon_heller » Thu Nov 09, 2006 12:00 am

An adhesive is usually used to hold the parts in place on the lower side of the board. A stencil may be used to apply the adhesive, like that used for the solder paste.

Leon
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teqdruid
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Post by teqdruid » Mon Nov 13, 2006 1:13 pm

leon_heller wrote:An adhesive is usually used to hold the parts in place on the lower side of the board. A stencil may be used to apply the adhesive, like that used for the solder paste.

Leon
What type of adhesive is typically used?

Thanks,
John

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leon_heller
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Post by leon_heller » Mon Nov 13, 2006 1:43 pm

Leon Heller
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teqdruid
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Post by teqdruid » Mon Nov 13, 2006 2:18 pm

Probably shoulda done that first.

Thanks for the help, both of you.

~John

NleahciM
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Re: Double Sided PCB SMT Soldering

Post by NleahciM » Mon Nov 13, 2006 11:30 pm

teqdruid wrote:Thanks for the tutorials on SMT soldering SFE!

A current design I'm working on requires that surface mount components be mounted on both sides of a PCB... Any ideas on how to solder them?

If I bought a hot air rework gun, would it heat the board enough that components on one side would fall off when working on the other side?

I've also seen solder paste available that melts at different temperatures. The low temperature ones seem to melt around 183 C, and the next grade up melts at 218 C, but that's 424 F, and the skillet I've got only goes up to 420F, according to the label. My toaster oven will supposedly go up to 500F, but I don't have much confidence in that.

Any thoughts?

~John
Assuming this is a low quantity device - why not just solder them with a soldering iron? That's how I still do pretty much 100% of my stuff - and that includes just about every surface mount package besides BGAs - With an iron you really can do just about anything.

teqdruid
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Re: Double Sided PCB SMT Soldering

Post by teqdruid » Tue Nov 14, 2006 4:46 pm

NleahciM wrote:
teqdruid wrote:Thanks for the tutorials on SMT soldering SFE!

A current design I'm working on requires that surface mount components be mounted on both sides of a PCB... Any ideas on how to solder them?

If I bought a hot air rework gun, would it heat the board enough that components on one side would fall off when working on the other side?

I've also seen solder paste available that melts at different temperatures. The low temperature ones seem to melt around 183 C, and the next grade up melts at 218 C, but that's 424 F, and the skillet I've got only goes up to 420F, according to the label. My toaster oven will supposedly go up to 500F, but I don't have much confidence in that.

Any thoughts?

~John
Assuming this is a low quantity device - why not just solder them with a soldering iron? That's how I still do pretty much 100% of my stuff - and that includes just about every surface mount package besides BGAs - With an iron you really can do just about anything.
Some of the devices I'm using are pretty fine pitch- my hand just isn't steady enough.

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leon_heller
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Re: Double Sided PCB SMT Soldering

Post by leon_heller » Tue Nov 14, 2006 11:01 pm

teqdruid wrote:
NleahciM wrote:
teqdruid wrote:Thanks for the tutorials on SMT soldering SFE!

A current design I'm working on requires that surface mount components be mounted on both sides of a PCB... Any ideas on how to solder them?

If I bought a hot air rework gun, would it heat the board enough that components on one side would fall off when working on the other side?

I've also seen solder paste available that melts at different temperatures. The low temperature ones seem to melt around 183 C, and the next grade up melts at 218 C, but that's 424 F, and the skillet I've got only goes up to 420F, according to the label. My toaster oven will supposedly go up to 500F, but I don't have much confidence in that.

Any thoughts?

~John
Assuming this is a low quantity device - why not just solder them with a soldering iron? That's how I still do pretty much 100% of my stuff - and that includes just about every surface mount package besides BGAs - With an iron you really can do just about anything.
Some of the devices I'm using are pretty fine pitch- my hand just isn't steady enough.
Use the drag soldering technique. Plenty of gel flux is the secret.

Leon
Leon Heller
G1HSM

NleahciM
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Re: Double Sided PCB SMT Soldering

Post by NleahciM » Wed Nov 15, 2006 8:39 am

teqdruid wrote:
NleahciM wrote: Assuming this is a low quantity device - why not just solder them with a soldering iron? That's how I still do pretty much 100% of my stuff - and that includes just about every surface mount package besides BGAs - With an iron you really can do just about anything.
Some of the devices I'm using are pretty fine pitch- my hand just isn't steady enough.
I'm sure they are. It really isn't as hard as it looks. You don't solder each pin individually.

Otatiaro
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Re: Double Sided PCB SMT Soldering

Post by Otatiaro » Wed Dec 29, 2010 10:28 am

Hello,

I'm having the same problem.

- I will have very high quality solder paste stencils for both side
- The board is 4 layer of copper
- The components are 0603 for resistors, LEDs and capacitors (one or two 0805)
- There are few small pitch QFN / LGA packages (one QFN64, a smaller QFN and an LGA package)
- I already solder my PCBs with hot air and pre-heater (all Aoyue)
- I've just bought a hot plate (not yet tested)
- I use leaded solder paste
- I can go to 6 layers if really needed.

I think I will need to place components on both sides.

Which components can be placed on the bottom side and stay in place during the second reflow just by surface tension (I do not have access to the required tools to put adhesive under the components) ?

- 0603 chips ?
- 0805 chips ?
- SOT23-5 chips ?
- LGA or QFN packages (around 20/28 pins) ?

Regards,
Thomas Legrand.

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