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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


REFLOWING 2 SIDED SMT BOARDS

JERRY JOHNSON

#11012

REFLOWING 2 SIDED SMT BOARDS | 16 June, 1999

WOULD LIKE TO DO RELOW OF 2 SIDED SMT BOARDS. USUALLY THE BOTTOM SIDE HAS RESISTORS AND CAPS ONLY. WHEN THE BOTTOM OF THE BOARD HEATS UP, THE PARTS ARE FREE TO MOVE AND ONLY SURFACE TENSION WILL KEEP THE COMPONENT FROM FALLING OFF. CAN BOARDS BE RUN LIKE THIS OF SHOULD THEY BE GLUED AND WAVE SOLDERED ONLY?

DOES ANYONE ELSE REFLOW BOTH SIDES?

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#11013

Re: REFLOWING 2 SIDED SMT BOARDS | 16 June, 1999

| WOULD LIKE TO DO RELOW OF 2 SIDED SMT BOARDS. USUALLY THE BOTTOM SIDE HAS RESISTORS AND CAPS ONLY. WHEN THE BOTTOM OF THE BOARD HEATS UP, THE PARTS ARE FREE TO MOVE AND ONLY SURFACE TENSION WILL KEEP THE COMPONENT FROM FALLING OFF. | CAN BOARDS BE RUN LIKE THIS OF SHOULD THEY BE GLUED AND WAVE SOLDERED ONLY? | | DOES ANYONE ELSE REFLOW BOTH SIDES? | Jerry,

The molten surface tension of the solder is more than adequate in keeping the parts from falling off during the 2nd reflow cycle(chip caps and resistors). If reflowing larger components, you might have to add an adhesive prior to placement.

Gary

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Dean

#11014

Re: REFLOWING 2 SIDED SMT BOARDS | 16 June, 1999

| WOULD LIKE TO DO RELOW OF 2 SIDED SMT BOARDS. USUALLY THE BOTTOM SIDE HAS RESISTORS AND CAPS ONLY. WHEN THE BOTTOM OF THE BOARD HEATS UP, THE PARTS ARE FREE TO MOVE AND ONLY SURFACE TENSION WILL KEEP THE COMPONENT FROM FALLING OFF. | CAN BOARDS BE RUN LIKE THIS OF SHOULD THEY BE GLUED AND WAVE SOLDERED ONLY? | | DOES ANYONE ELSE REFLOW BOTH SIDES? | "can boards be run like this or should they be glued and wave soldered only?" The determining factor generallly is governed by your product requirements and process capability. Example: If you don't have a glue machine then how can you epoxy. Or you could print the glue. If you did not have Thru-hole components(on the board) why wave solder? Why over complicate the process? Or if you did have TH components can you use selective soldering?

Or what if you don't have a wave solde machine? Or if you have TH parts and did not glue you could still selective solder. I perfer a paste-paste process for double sided assemblies. It inherently has a lower defect rate (the process) than its counterpart (wave solder) AND reduces the required manufacturing steps to achieve a completed product. 90 % of the products I produce are two sided. My two cents... Dean

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Brian Wycoff

#11015

Re: REFLOWING 2 SIDED SMT BOARDS | 17 June, 1999

| | WOULD LIKE TO DO RELOW OF 2 SIDED SMT BOARDS. USUALLY THE BOTTOM SIDE HAS RESISTORS AND CAPS ONLY. WHEN THE BOTTOM OF THE BOARD HEATS UP, THE PARTS ARE FREE TO MOVE AND ONLY SURFACE TENSION WILL KEEP THE COMPONENT FROM FALLING OFF. | | CAN BOARDS BE RUN LIKE THIS OF SHOULD THEY BE GLUED AND WAVE SOLDERED ONLY? | | | | DOES ANYONE ELSE REFLOW BOTH SIDES? | | | Jerry, | | The molten surface tension of the solder is more than adequate in keeping the parts from falling off during the 2nd reflow cycle(chip caps and resistors). If reflowing larger components, you might have to add an adhesive prior to placement. | | Gary |

We do quite a few double sided boards, and have no difficulty in the parts falling off without gluing them. in previous incaarnations, I have double side reflowed boards with ICs on both sides. Most of the convection ovens I am familiar with have the capability to reduce the temperasture setting for the bottom side of the board if necessary. Double sided reflow, including use of intrusive reflow techniques, have provided better quality, more robust processes, and better cycle times. As mentioned, your process should be defined by your product complexity, design, and manufacturing capabilities. Define your process parameters and experiment with them to find the best combination for your product.

Brian

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Dick Casagrande

#11016

Re: REFLOWING 2 SIDED SMT BOARDS | 13 July, 1999

| WOULD LIKE TO DO RELOW OF 2 SIDED SMT BOARDS. USUALLY THE BOTTOM SIDE HAS RESISTORS AND CAPS ONLY. WHEN THE BOTTOM OF THE BOARD HEATS UP, THE PARTS ARE FREE TO MOVE AND ONLY SURFACE TENSION WILL KEEP THE COMPONENT FROM FALLING OFF. | CAN BOARDS BE RUN LIKE THIS OF SHOULD THEY BE GLUED AND WAVE SOLDERED ONLY? | | DOES ANYONE ELSE REFLOW BOTH SIDES? | Look at archives here.4/2/99 Subject "qfp's on backside"

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