4. Electronics production¶

This week i make an in-circuit programmer by milling and stuffing the PCB, and test it.

the material¶

the milling machine¶

we use the Roland SRM 20. the machine can mill Modeling Wax, Chemical Wood, Foam, Acrylic, Poly acetate, ABS, PC board (PCB)

srm20

0,4 or 1 mm endmill is small and, even with the lowest position, the spindle cannot reach the PCB blank on the table. You need some extra spacers. We do that with several MDF joined layers, which become the sacrificial board when the milling is too deep.

hauteur-mouvement

cutting-area

You have to be carefull when you install the endmill because it’s very fragile. Don’t let it fall

fraise

The machine it self has a “hardware” zero position (x,y and z) but your job a one as well. you will have to set the 0 level of the Z axis of your job, depending on the attachment of the endmill . The x,y depends on where the PCB blank is installed and also depends on your design

this machine accept 2 Languages : RML-1 (roland standard) .rml , NC code (general language) .nccode

principle

The soldering station and small equipment¶

solder station2

Our soldering station is the weller PU 81

and we use it at 400°c

all our boxes, tools and tweezers are ESD, to avoid from static electricity problems.

tweezers

box for component box

we use Brass Tip Cleaner, magnifying lamp on stand, desoldering braid or pump to vaccum a missed weld

The solder wire without lead¶

solder

Characterisation of the milling machine¶

with linetest_trace and linetest_interior

we drawed

characterisation

we can see the engine succeed to mill all the line but the thinnest (0.1 inch) was to fragile and we removed some copper with the fingers. and for the space, the thinnest we mill 1.9 inch

the different steps.¶

Preparing the milling¶

Mods¶

first, you have to choose the in-circuit programmer. For me, it’s CMSIS-DAP.10.D11C.

you need 2 .png files :

for the trace (to remove the thin layer of copper)
for the cut of the exterior (to detach the work from the entire board)

hello.CMSIS-DAP.10.D11C.traces

hello.CMSIS-DAP.10.D11C.interior

because it’s .png files, with a large zoom we see the limit of the fineness of the drawing up to the pixel limit.

mod2

2 files because you need to mill 2 times with different endmill and different deep and speed

to prepare the files, we use mods. Mods does not work with Edge. So we use Chrome.

mods1

those first choices will open a more detailed screen

mods2

mods5

mods4

the different criteria to monitor¶

mods7

A : size of the endmill
B : deep to cut on each pass (never more than half size of the endmill)
C : total of the deep to cut
D : number of offset to enlarge the cut
E : movement speed
F : other elements. keep at 0

	trace	interior
Endmill	0,4 mm	1 mm
total to cut	0,1 mm	1,7 mm
deep to cut each pass	0,1 mm	0,3 mm
number of offset	4	1
speed	2	4

configuration for the trace file¶

mods8

detail of the movement of the endmill

mods25

configuration for the interior file (cut of the piece from the board)¶

mods9

If no file is generated, there is a configuration problem

VPanel for SRM-20¶

on the computer linked to the milling machine, i use VPanel for SRM-20 for 2 main actions :

adjusting the position of the endmill (x, y, z)
outputing the files to the milling machine

The PCB Blanck¶

I used double side tape to fix the PCB blank to the sacrificial board. The tape must be laid precisely without bubbles. The PCB blank must be glued as strongly as possible and as horizontal as possible.

Technical data of our PCB FR-1 (FR = Flame retardant) : Bare copper card, Simple face, 150 x 100 x 1.6mm, 35μm, reference constructor

X Y of the milling machine.¶

mods10

Z of the milling machine.¶

. mods11

you can loose the set screw, and adjust the cutting tool so that its tip contacts the surface of the material, but you have to support lightly by hand not to drop a the endmill