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July/August 2018

PCBs With PTHs

Is there a hobbyist method for making circuit boards with plated through holes at home? Also curious by what is meant by multilayer boards. I'm just getting started, so forgive if this is an obvious newbie question.

#7185
Leonelo Márquez
Maplewood, MN



Answers

I gave up making boards years ago. Hazardous chemicals, lots of fiddly fine work. Double side boards require precise alignment, and multilayer boards are impossible at home.

A multilayer board is a board that has conductive layers sandwiched inside the board, usually one for power and one for a ground plane — for a total of four layers (top, ground, power and bottom). More layers are also possible, of course.

Jay R Jaeger
Madison

Etch or mill your circuit boards with space for larger holes where you need them to be plated thru. Insert small grommets made for that purpose into the holes and peen them over. In most cases this will be unnecessary because you can just solder parts like resisters on both sides of the board.

The use of sockets will make working with IC’s, DIP switches, and resister arrays much easier.

Multilayer boards are made up of several thin circuit boards glued together. Four to eight layers are common. The plated thru holes often do not reach the surface of the finished board. You can achieve much of the same effect by adding a daughter board (a shield in Arduino terms), to your design.

Dale Freye
via internet

I don’t know of any easy way to make plated-through holes using home brew PCB etching materials. However, if you use double-sided copper-clad boards, you could make front and back etching screens. Just make sure you securely attach the front etching screen to the blank and re-drill your holes from the front side.

Then, using the drilled holes as a guide, securely attach the back screen to the blank, ensuring you accurately line it up the drilled holes. Then, with both screens still attached, expose both sides of the blank (assuming photo-resist is used), remove the screens, then develop and etch the board.

When you install the components on the front side, ensure you solder both sides of the board where a lead makes a front to back connection.

As for multilayer boards, they’re exactly what the description is. They’re a sandwich of thin boards, each layer typically 1 millimeter thick, with etched circuitry (single or double-sided) or an un-etched power or ground plane, glued together in exact (i.e., 1/10000” or better) alignment so all the through-holes will match-up when components are installed.

When completed, these boards can be as thick as 5 millimeters or so, with 8 or more layers! Most multi-layer boards use through-hole plating, especially on power and ground planes, to ensure positive through-hole connections (again, depending on how well each layer is aligned when the sandwich is made).

They’re soldered using wave-soldering equipment because hand-soldering risks damaging the board via local overheating, especially when soldering to an internal power/ground plane or even bad solder joints (the solder doesn’t make the connection on internal layers), which is why they’re very expensive to design and manufacture.

Ken Simmons
Auburn, WA

Answers to “newbie” questions always help others. You can create plated through holes in your workshop, but it involves many steps with chemical solutions.

Instead of messy and toxic chemicals, why not solder a jumper through the board to connect conductors on both sides? As an alternate, use component leads to make a side-to-side connection and solder the leads on both sides of your board.

If you truly want plated-through holes, contact a PCB fabricator that will make a run of three or four boards for you with plated-through holes. I have used ExpressPCB and a friend has used OSH Park, both with good results.

A multilayer board has etched copper layers sandwiched between insulating layers and connected with tiny plated-through holes. Search Google for multilayer PCB and you’ll find many helpful cut-away diagrams.

Jon Titus
Herriman, UT