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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


SMT assembly

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#58298

SMT assembly | 9 March, 2009

I have a double sided assembly board having more no. of QFP's & IC's at both Top & bottom.Is there any concern about this??.COz. i have the profile set to be almost same for Top & Bottom.Worried whether bottom side IC's fall/ Shift during Top side reflow.

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#58304

SMT assembly | 9 March, 2009

Bob Willis and Phil Zarrow have published recommendations in this area. * Search the fine SMTnet Archives for references to their findings. * Read posted papers on the topic on their sites.

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#58308

SMT assembly | 9 March, 2009

Here is a formula that may help. C/P

C= Component's weight in grams P= Total pad area in Sq. in.

Must be less than or equal to 30

Parts larger than a 68 pin PLCC should use an adhesive. Hope this helps.

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#58313

SMT assembly | 10 March, 2009

First evaluate yoru Reflow Oven: does it have independant temp control for Top and Bottom Heaters? This is a MUST.

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#58321

SMT assembly | 11 March, 2009

No, it's not. Bottom components will reflow regardless of bottom side heaters.

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#58322

SMT assembly | 11 March, 2009

surface tension is what holds the parts on when solder is flowing I would add some glue under the parts that I placed on the frist side the glue will add more surface tension. this is if you have a glue dispencer in your line already.

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#58325

SMT assembly | 11 March, 2009

Make sure your oven conveyor is running smooth as well. One bump or bad vibration will knock parts off too.

Lowering the bottom zones in spike zones will help too.

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#58342

SMT assembly | 13 March, 2009

Thx a lot brown.Well this worked out better. earlier i had tried using a heat resistant tape on the component ended up with issues. Thx Nagesh

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#58359

SMT assembly | 16 March, 2009

Hey Loco, how about saving the bottom side? It actually only depends on your oven setting specific to Top heaters and Bottom heaters. Unless you set the parameters rightly, you would face such issues. It only indicates that you need to seriously re-look your profile. The key is to have lower Bottom heater temperatures and optimise the conveyor speed to allow Top side heaters to do their job, without affecting either side in a negative way. Get it ?

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#58364

SMT assembly | 17 March, 2009

No. It took you 5 sentences to tell me absolutly nothing. Let me guess, you're a consultant to managers or worse yet, a manager?

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#58365

SMT assembly | 17 March, 2009

Thanx, I never thought I was that good. - Cheers !!!

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