Catching up the development of printed circuit boards at home i often faced with the problem of “the bulbous” vias. Usually homemade double-layer boards soldering from both sides with the thin wire, the result usually satisfied but if you need to make VIA under the chip TQFP48, SOIC16 and that’s is a real problem, if contact is very bulbous it will be simply impossible cleanly solder chip as its legs will hang in the air.
I suggest you create your own version of flat vias.
Creating quality board begins with the development of high-quality template for illumination Resist. I created the PCB in program EAGLE it is very comfortable and in internet is enough libraries elements and examples of use.
1.I cut out board with a offset of 15 mm on each side bigger than the resulting board.
2.Before application of Resist carefully grind with a sandpaper (especially the edges of burrs) wash with powder detergent such as “Gala” and sponge
The surface of the board is usually dirty and oily so wash and rinse until the powder sponge stops become dirty color.
3. Thoroughly dry thethe bord if you need to do it quickly, you can use soldering station Blower fan for soldering SMD.
4.Resist Pozitiv 20 must be applied at once on the whole surface of the board.
5. Give resist dry during 1 hour placing it in a horizontal position in a dark place.
6. It is time for the stencil. I test various methods DIY stencils, I stopped in the film version of industrial stencil.
I order it at the company that makes business cards and printing service called “Foto on film.” PCB printed Eagle through Bullzip pdf printer and import CorelDraw and a file i had sent to the printing the company. Stencil comes out perfect I do with it tracks 0.2 mm wide. I usually order film A4 it fits a lot boards of my and my friends.
7. Stencil impose a board on Resist and lighted by UV lamp for 3 minutes.
8. After exposure we must give a Resist to polymerized as leaving it in a dark place for 40 minutes.
9. Wash the board in a solution of NAOH (you can also use the tool for cleaning pipes “Krot” is the same NAOH available at hardware stores) in proportions indicated on the tank with Resist.
10. Give the board time to dry.
11. The lower part of board cover by duct tape.
12. Etch board in ferric chloride.
13. Once board etch for precise positioning of lower layer you must drill 2-3 via holes through them we will set a bottom stencil by those holes. It is important to drill the holes perpendicular to the surface of the board. For this I made a simple drill with a motor from an inkjet printer and carriage from the CD drive as the return spring is now used cash rubbers))))).
14. For lower layer Repeat steps 2 -12
You will get such a piece.
this is the board with tracks 0.2mm. Note the padding on the sides of board we will need them soon
15. Drill the remaining holes.
16. Cover with tin charge.
17. Proceed withVIA contacts.
1.17 cut off copper wire 0.2mm diameter.
17.2 covers the tin it.
17.3 Flatten out it at a distance equal to the radius VIA.
17.4 Flatten tip bends at 90 degrees.
17.5 Insert into the hole and solder with the front side.
17.6 Solder it from the back side.
17.7 Repeat with all the holes.
18 .Final chord. Sand the bulbous of VIA on both sides, with such a device
made of aluminum corner with a glued on it pice of sandpaper (glued with a double sided duct tape)
Sand it to desired height Via.
That’s where needed a offset on the board they take a stab at themselves and protect final board size.
Voila shiny boards without mistakes and broken legs!