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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


PCB Support

Stephen

#8384

PCB Support | 30 November, 1999

Hello All,

We assemble boards which are small in size. We use nests for support when screen printing the boards. The nest gives support along the edges of the board. However we are bringing in a new product which has components very close to one edge of the board thus preventing us from supporting this edge when printing the 2nd side. There is also no space for pin support. We are worried that without the extra support it will lead to solder bridges etc.

Does anyone have any ideas for alternative support? Is it safe to support the board from underneath the components (TSOPs)?

Thanks, Steve

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#8385

Re: PCB Support | 30 November, 1999

Hi Steve, is it possible for you to get more than one PCB in a panel and separate them after assembly. Some kind of framepiece for support at the affected edge later to be separated should do it as well.

My first ideas

Wolfgang

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Mike Moninger

#8386

Re: PCB Support | 30 November, 1999

A really nifty nest can be made by making an RTV mold of the first side of your assembly. Assuming all are identical within some small tolerance, the resulting mold holds the board very securely and distributes the loading. Cover the components with a layer or two of saran wrap to minimize the mess and give a little extra clearance. I believe that someone advertises this scheme in SMT magazine. It's probably not a good idea to try to support the board by the components. There could be some very high instantaneous loading as the squeegee passes. Mike

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#8387

Re: PCB Support | 30 November, 1999

Continuing, many soldering pallet manufacturers make pallets with pockets to support bottom-side components during second side processing.

Good luck

Dave F

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Stephen

#8388

Re: PCB Support | 1 December, 1999

Wolfgang,

For most of our products, we use a 3-up panel. However for each PCB in this panel we will have a support problem beacuse of the components close to the edge.

The framepiece you mentioned - is this something that would come from the PCB supplier or is it something we would do ourselves?

Thanks, Steve

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#8389

Re: PCB Support | 1 December, 1999

Hi Steve, the "framepiece" I mentioned may be misunderstanding but sometimes I don�t know the common english expression. What I meant is if the PCBs do not come in panels (now you mentioned 3-up panel)the PCB supplier could add additional material to that specific edge with Breakaways or V-grooves for later separation. We had this feature for PC-boards to protect the connector area during assembly and support for the beltsystems. Picture of this for example can be seen in IPC-SM-782A chapter 3.6.4.6

Hope this is clear enough

Wolfgang

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Chris McDonald

#8390

Re: PCB Support | 4 December, 1999

We had a simular problem We used EMC GLobal Technologies. Basically had carriers mad for small cards. It worked well and we could reflow and wahs the pallets too.

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sin

#8391

Re: PCB Support | 7 December, 1999

Like Wolfgang said, the breakaway tab is just another bar added to the edge of the pcb. This breakaway tab can be added by the FAB house in addition of extra cost...You can write DFM for your customer to see if they will pay for the cost or not...if not then you need to order pallets fixture for machine such as printer, pick and place. This pallets can order from the stencil house in amount of say 5-10 for pick and place, and one for printer. Please correct me if i am mistaken

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