Electronics > Altium Designer

"IT'S TOO BIG!" says everyone, including my PCB assembler...

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Alti:

--- Quote from: frogblender on October 08, 2021, 07:41:31 pm ---it won't fit in the smt machine, won't fit into x-ray, won't fit into the reflow oven, and just plain won't fit.
--- End quote ---
What is the maximum panel size standard accepted in PCB assembly houses? Obviously this varies but there must be some kind of standard that is commonly accepted. Of course bare PCB manufacturing is one thing and then P&P process max panel size is another. I am asking for the latter.


--- Quote from: free_electron on January 20, 2022, 06:05:18 pm ---one part of the board will be in reflow while the other is still burning off the flux. this is going to give tremendous stress on the board.
--- End quote ---
I cannot see what could be different in the process if you feed ten boards of 0.1m length one by one or just a single 1m board. I assume there are no 1m long single piece components that stretch whole length.

mikeselectricstuff:

--- Quote from: Alti on January 21, 2022, 11:55:21 am ---
--- Quote from: frogblender on October 08, 2021, 07:41:31 pm ---it won't fit in the smt machine, won't fit into x-ray, won't fit into the reflow oven, and just plain won't fit.
--- End quote ---
What is the maximum panel size standard accepted in PCB assembly houses? Obviously this varies but there must be some kind of standard that is commonly accepted. Of course bare PCB manufacturing is one thing and then P&P process max panel size is another. I am asking for the latter.

--- End quote ---
This varies for every subcontractor, depending on their equipment, and also by the type of assembly ( e.g. single/double sided, PCB thickness, stencil requirements etc.). Each part of the process will have different limits, e.g. a place I use can do up to 1.6m, but their auto stenciling system only does about 1.2m, so longer boards need to be hand-stencilled, with reduced accuracy, so it's fine for dumb LED strips, not so much with SSOP drivers on the back.
Somewhere around 350x450mm is a fairly common maximum.

Alti:

--- Quote from: mikeselectricstuff on January 21, 2022, 12:18:19 pm ---(..)Somewhere around 350x450mm is a fairly common maximum.
--- End quote ---
I guess the machinery is made to match imperial panel sizes.
I did some investigation, some sources like this one suggests 12" x 18" (304.8mm x 457.2mm ) which is close. Also here and here. Then PCBWay have it 530mm x 330mm (close to 13" x 21").

Some sources give 18" x 24" as standard PCB assembly panel but I guess this requires really specialized gear.

Might it be that 18" x 24" size is popular for mainstream PCB production and then this is chopped in half and 12" x 18" panels slide through PCB assembly?

free_electron:

--- Quote from: Alti on January 21, 2022, 11:55:21 am ---
--- Quote from: free_electron on January 20, 2022, 06:05:18 pm ---one part of the board will be in reflow while the other is still burning off the flux. this is going to give tremendous stress on the board.
--- End quote ---
I cannot see what could be different in the process if you feed ten boards of 0.1m length one by one or just a single 1m board. I assume there are no 1m long single piece components that stretch whole length.

--- End quote ---

your 0.1m board will be hot all at the same time. that super long board will be half hot , half cold. this causes a ripple effect. i've seen boards used in MRI machines. they need special long zone ovens , or have an oven with dynamic conveyer speed.
the problem is that the total dwell time in the various zones need to be quasi constant. the flux activation time is much longer than the reflow time. so you get into issues timing the conveyor. they traditionally solve this by having a constant conveyor speed , a long flux zone and a short reflow zone. the longer you make the reflow zone the longer the flux zone needs to get. the travel speed determines the time in a zone. so if you need a hot zone of 1 meter ( which is good for a 3/5 to 3/4 meter board ) your flux zone is much longer ( 4 to 5 times that ) or you need a conveyor that can speed up ( but not too much as you don't want thermal shock ). Getting the speed and zone size right is going to be a problem. you want the board to go in fast enough , but not too fast to avoid thermal shock , sit in the flux zone for a minute or two then go through reflow for 15 to 20 seconds , then cool down.

The ovens do not ramp temperatures. this is not a converted pizza oven you use at home ! the oven is a long tunnel with various areas at different temperatures. these ovens have a large thermal mass so the zones dont influence each other and the board does not alter the inside temperature. it takes 24 to 48 hours to switch such a thing on .... altering the temperatures to accommodate 'crazy' boards will take a lot of time to reach setpoint.

your other problem will be thermal uniformity.

https://hellerindustries.com/reflow-oven/

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