Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Double sided SMT, bottom side first or top side first ?

Yngwie

#23627

Double sided SMT, bottom side first or top side first ? | 4 March, 2003

In the double sided SMT process assembly, normally the bottom side will be processed first, due to it's lesser density as well as it's lesser heavy components. Apart from worrying about the component falling down, what are the potential problems that you guys think that this process will lead to ?

thank you

reply »

MA/NY DDave

#23637

Double sided SMT, bottom side first or top side first ? | 4 March, 2003

Hi

Unless I am missing something, None if done right.

YiEng, MA/NY DDave

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

reply »


mr

#23652

Double sided SMT, bottom side first or top side first ? | 4 March, 2003

Most of what we do (across 800+ varieties) is bottom side first. In general, there really aren't any problems as long as our Customers follow the .25g/cm wetted lead perimeter spec for weight (which many don't), and don't mount tall components on the b-side. If these aren't followed, we get to figure out how to process the board. This includes A-side first, but more likely, we will use epoxy (Loctite 3609) on the part or high-tack vacuum grease from DOW to secure the component. Or, we move the part to a Handsolder process and the Customer incurs the additional cost.

Good luck, MR

reply »

Yngwie

#23659

Double sided SMT, bottom side first or top side first ? | 5 March, 2003

Thanx Marc..this is good input.

reply »

#23700

Double sided SMT, bottom side first or top side first ? | 7 March, 2003

Hi Ygwie, My experience shows there is not unique answer.Actually it depends on design,printing reflow or wave.It might be top side with lesser cmps.Top side might have fine pitch or BGA or CSP,LLGA ....,so you have better planarity when the PCB is bare. I think it depends on the case, so you decide which side first. I am doing it that way and it works.

reply »

reflow oven profiler