PCB Design - SMD components on bottom side

nwrightson

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Subject:

PCB Design - SMD components on bottom side

· Posted: 17.05.2011 - 01:40 · #1

Hi All,

I'm designing a PCB using surface mount components and I'm runnng out of room on the top side.

For the first few PCB's, I will probably hand assemble the prototypes myself but after that, I'm thinking of getting them commercially assembled.

So is there any thing I need to consider in regard to components on the bottom side?

Basically, I guess what I'm concerned about, is reflow ovens and the components falling of the bottom side whilst the top side is been soldered ???

The components I'm looking at putting on the bootom side are thngs like SMD RJ45, 0603 caps/Res, crystal, QFN48 etc.
Actually similar components on both sides. So I guess it makes no difference which side gets soldered first.

Thanks, Neil.

Thomas vb

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Subject:

Re: PCB Design - SMD components on bottom side

· Posted: 17.05.2011 - 10:10 · #2

Hi Neil

you need a separate stencil for the bottom solder paste. With a reflow oven it should work to solder the top and the bottom parts in separate pass.
But a lot of productions use vapor phase soldering. The vapor has the same temperature below and on top of the print, the bottom side components will then fall down.
A specicial adhesive for SMD parts is available. It become hardened at obout 100 - 150 C in some minutes. I seldom use that adhesive. It is very toxic.

Regards
Thomas

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