Tools of the Trade – Through Hole Assembly

In our last installment of Tools of the Trade, we had just finished doing the inspection of the surface mount part of the PCB. Next in the process is the through hole components. Depending on the PCB, the order may change slightly, but generally it makes more sense to get all the SMT work done before moving to the through hole work.

Through hole used to be the standard, but as the need for size reduction and automation increased, SMT gained favor. However, there are still a lot of reasons to use through hole components, so they aren’t going away entirely (at least not any time soon). One of the biggest advantages of THT is mechanical strength, which makes it better suited for connectors than SMT. If you’ve ever popped a microusb connector off a PCB by breathing on it heavily, you’ll understand. So, how do we most efficiently get through hole components on a PCB, and how do the big boys do it?

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PinJig Soldering Clamp has Pins Seized by Airport Security

There’s an old adage that when performing a live demo, previously working hacks will mysteriously go awry. In this case, the hardware demo was doomed before it ever arrived at the conference.

PinJig is an interesting take on though-hole soldering. As its name indicates, it’s a jig which holds through-hole components in place as the board is flipped on its side (or even upside down). This is accomplished by 2000 steel pins which are locked in place after being nestled around all of the board’s components. Unfortunately, carrying this prototype onto an international flight didn’t work out. [Niall Barrett] told us that on his way from Ireland to Bay Area Maker Faire he was required to ditch the 3-inch steel pins that make up the jig, or not get on the plane.

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Via press crushes copper to make a mechanical connection

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[Jay] was looking for a way to make his own vias on homemade double-sided PCBs when he stumbled across this post from about five years ago. The technique shown here makes mechanical vias and was developed by [Retromaster]. There’s no soldering involved, instead he uses some solid core copper wire and a press to crush it tightly against the board.

The press is made from aluminum stock, with a couple of plates of stainless steel which come in contact with the board. The aluminum stock is easy to work with, but it’s relatively soft which is the reason for the addition of steel. He uses copper wire which already fits tightly in the hole through the substrate. After clipping off the excess as near to the board as possible a trip through the press leaves each side flat as shown in the inset image.

We looked through some of the other projects we’ve seen from [Retromaster] like the Atari 2600 in an FPGA and this emulated Amiga floppy drive. But we didn’t see any diy boards where he used this crushing technique.

Through hole plating and milling at home

Here’s a PCB fabrication process that makes us envious. It’s pretty darn close to fab-house quality at home. [Cpirius] is using a CNC mill and through hole plating technique to produce his double-sided circuit boards.

The video embedded after the break shows one board from start to finish. It begins with the mill drilling holes through some double-sided copper clad stock. Once the millings have been cleaned off the holes are coated with a mixture of waterproof ink and carbon. This prepares them for plating by making the holes themselves conductive. The board is then run through an electroplating process based on this guide.

Possibly the most interesting part of the process starts 52 seconds into the clip. The mill uses a conductive probe to generate a height map of the entire board. This allows it to vary the routing depth for perfectly cut isolation traces. That final routing process is pictured above.

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PCB drill from R/C car parts

[Sid] makes a few PCBs a month and the hardest part of his fabrication process is always drilling the through-holes. He has a PCB hand drill that usually results in a sore index finger. After a few unsuccessful attempts of using a full-size electric drill and not wanting to invest in a commercial solution, [Sid] made a PCB drill from a broken R/C car.

The toy car was donated by [Sid]’s 4-year-old after a terrible crash. [Sid] took the gearbox from the car and added a small circuit to control the direction of the drill. After attaching the drill chuck to the former R/C car axle and adding the power leads to a 5 Volt adapter, a PCB drill press was born.

Most of the parts for this build were salvaged from the toy car’s radio control circuit. Except for the chuck from [Sid]’s hand drill and a few switches, everything on this build was pulled from a broken remote control car. While the build is a lot simpler than this semi-automatic PCB drill, [Sid]’s drill seems to work well. Check out the demo video after the break.

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Semi-automatic PCB drill press

Kiss the days of breaking bits while drilling through-hole PCBs goodbye thanks to this semi-automatic drill press (translated). Now it’s not going to line up the bit with the exact location of the hole (that would make it a fully automatic drill press). This works by lining up the board manually, then stepping on a pedal to activate the plunging motion of the drill.

A linear motor is responsible for the smooth, accurate motion along the Z-axis. Many hobby setups use a Dremel drill press, or even rely on prayer-based systems such as doing it free-hand with a rotary tool or by using a piece of acrylic as a guide hole. The hobby drill press tends to have some play in it and free-handing with tiny bits that are as fragile as glass both result in far too many broken drill bits. In the video after the break you can see that the linear motion is perfectly plumb with the table of the device, preventing the movements that cause breakage. The addition of the pedal makes it easy to position the boards because you can use both hands.

Having a tool like this takes all of the frustration out of using through-hole parts.

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Through-hole Bus Pirate kit from Fundamental Logic

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Fundamental Logic is selling a Bus Pirate kit and bare PCB based on our universal serial interface tool. They started with our serial port-based v1a hardware, and modified it to use all through-hole parts.  8pin DIP LP2951ACN/-3.3 switchable voltage regulators replace the surface mount TPS79650/33 that we used. The PIC is pre-programmed with our latest firmware, version 0f, which includes a bootloader for easy firmware updates through the serial port. Documentation includes illustrated assembly instructions.

Speaking of Bus Pirate goodness, we’re busy working on hardware V2. As astute readers may have already noticed, the final version of the Bus Pirate incorporates an FTDI USB->serial chip, and draws its power from the USB port. We also tackled the software-controlled pull-up resistor feature, and reduced the overall part count and cost. Best of all, we’re working to make assembled PCBs available with world-wide shipping. The how-to should be ready in a few weeks.