Author Topic: Home PCB prototypes and assembly.  (Read 1590 times)

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Offline jmelson

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Re: Home PCB prototypes and assembly.
« Reply #25 on: February 16, 2018, 10:31:23 am »
[
What's the finest size you've done?  QFN and/or LGA?
I regularly do 0.5mm 144-lead FPGAs, but have done 0.4mm stencils, and they came out OK.  That is really pushing the limits, my photoplotter is 1000 DPI, so those apertures were only about 7 pixels wide.  I generally hand-solder those chips as they are custom ASICs and my P&P is not accurate enough to align them well.  The thinner stencil helps keep the amount of solder paste from being too much, and it also etches quicker with less sideways etching under the resist.  I only do leaded parts.  I did do one board with 65 leadless chip-scale comparators on it, but had LOTS of solder shorts under the chips.  Drove me MAD fixing all that!

My laser photoplotter is quite accurate, it aligns well to the PC board even with a board 10+ inches wide.  You probably will never get that good overall alignment with a laser printer.

Jon
 

Offline Mark

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Re: Home PCB prototypes and assembly.
« Reply #26 on: February 16, 2018, 09:48:02 pm »
Are all those vias riveted?

How much time from setup to soldering did the PCB take?

All vias riveted using the Favorit press and 0.6mm internal rivets. 
https://www.megauk.com/through_hole_rivets.php
The bottom part of the tool set has a spring loaded pin and the top part has a fixed pin.  I've broken it twice but found that it still works well even without the fixed pin.  To eliminate the risk of the rivet making a bad contact to the via copper, I now place an octagonal SMT pad top + bottom so that the rivet gets pasted with solder. 

The steps are:

1.   When creating the print preview in Altium, mirror the TOP layer so that the toner is next to the PCB. 
2.   Print onto LaserStar transparencies using the HP LaserJet Pro M201dw. 
3.   Warm up the LV204 UV exposure box for 1000 seconds. 
4.   Expose for 120 seconds. 
5.   Develop the image on the PCB. 
6.   Pre-warm the bubble etch tank and etch at XX?C for approximately 15 minutes. 
7.   Clean with methylated spirits or acetone, then used deionised water and wire wool to get a really clean and shiny surface. 
8.   Ensure the board is perfectly clean and dry, then immerse in tin plating solution for 10-15 minutes or in “Liquid Tin” for 3-5 minutes. 
9.   Wash and dry the board. 
10.   Pre-warm the laminator. 
11.   Cut a hole in a piece of cardboard the same size as the PCB.  The cardboard will become a carrier for the PCB as it travels through the laminator. 
12.   Remove the matte side from the dry-film soldermask and apply to one side of the PCB as it goes into the laminator. 
13.   Apply the dry film soldermask to the other side of the PCB. 
14.   Pass through the laminator several times. 
15.   Expose to UV for 60 seconds. 
16.   IMMEDIATELY after exposure, the top piece of gloss polyester liner should be removed and the panel allowed to stand for 15-20 minutes. 
17.   Develop the soldermask with agitation and use a soft brush over the surface. 
18.   Cure the soldermask for 30 minutes in the UV unit, then at 100°C in a fan oven for 1 hour.  (Alternatively, expose for 1 hour in the UV unit). 
19.   Drill with 0.8mm bits for the through-holes and install the 0.6mm (internal diameter) Bungard rivets. 
20.   Create stencil files and send to Silhouette portrait (A4) craft cutter.  Stencil cutting is much faster when there are fewer angles, so avoid round holes where possible, use octagons instead. 
21. Apply the solder paste and place the components. 
22.   Pop it in the oven. 






 

Online rx8pilot

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Re: Home PCB prototypes and assembly.
« Reply #27 on: February 17, 2018, 05:11:07 am »
Any estimate of the total end-to-end time for the PCB portion (excluding the paste, placements, and re-flow)

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Offline Mark

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Re: Home PCB prototypes and assembly.
« Reply #28 on: February 19, 2018, 03:18:04 am »
Any estimate of the total end-to-end time for the PCB portion (excluding the paste, placements, and re-flow)



Probably 2 or 2.5hrs in total to include drilling, riveting and cutting/trimming edges. 
 
 

Online rx8pilot

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Re: Home PCB prototypes and assembly.
« Reply #29 on: February 19, 2018, 05:53:09 am »
Wow, that is actually quite impressive. I did not expect such a short turnaround.



Short and misplld from my mobile......

Factory400 - the worlds smallest factory. http://www.youtube.com/c/Factory400
 

Offline noras

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Re: Home PCB prototypes and assembly.
« Reply #30 on: March 05, 2018, 06:57:32 pm »
I personally think that the prototype assembly can be done at home, otherwise, you have to buy the components and then sent to the factory assembly, and then sent back by courier, the whole process is too cumbersome, the cost is high.

An electronic assembly at home goes through six steps:

Paste Stenciling
Placement
Reflow
Manual Assembly
Inspection and Testing
Washing


Doing solder reflow work can be expensive and difficult, but thankfully there exists a simple and elegant solution: Toaster Ovens.
« Last Edit: March 05, 2018, 07:09:31 pm by noras »
 


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