Community Spotlight: Rudolf Riegel, an EE at WMT

At WMT GmbH in Stuttgart, Germany, turning ideas into tangible products is what drives the team. Specializing in electronics, software, and prototype assembly, WMT is all about innovation and efficiency.

Today, we’re speaking with Rudolf Riegel, an electronics engineer who joined the company through a chance encounter and has since become a key part of their operations. 

The LumenPnP is helping them cut their production times in half, while producing small batches of boards quickly and cost-competitively. They plan to purchase the new LumenPnP V4 in the future as production grows.

Tell us a bit about yourself and what you make.

My Name is Rudolf Riegel, and I'm an electronics engineer at WMT GmbH. WMT - Wir machen Technik (we make technology) is a young engineering company in Stuttgart, Germany. We bring ideas to products. We develop and build the electronics, write the embedded software, design the casing and other mechanical parts, and assemble prototypes and small series.




I've been into engineering since a young age and studied mechatronics automation and power electronics. I came to WMT by coincidence, going to a visit to the "Innoport" (an open Workshop and Startup accelerator located in Reutlingen) with friends - and Max Kessler, Co-Founder of WMT. The company was looking for a helping hand for electronics assembly, and the journey began.

What are you building with your LumenPnP? 

We do all kinds of boards for development and small batches, up to a few dozen to hundreds. Some boards contain only a few parts, some several hundred. The Lumen mainly places 0603 passives and some ICs, but we are starting to use 0402 parts.

Did you build or buy a LumenPnP? 

We bought the machine.

I adjusted the bottom vision to the same height plane as the PCB is sitting on quite early.

The cable to the nozzle motor broke a few times; lots of hot glue and not guiding the cable through the zip tie on the head solved the problem (the head was redesigned later, so this problem no longer exists on new machines).

We do not use the vacuum sensor. The machine aligns all parts with the bottom vision, so unpicked parts will be detected anyway.

The service of Opulo is also very good; we got a replacement power supply (after putting more than 30 feeders on the machine, the original was not up to the task). One of the vacuum pumps died - a replacement arrived very fast.

 

What is your favorite feature of the LumenPnP?

The feeders.

How many boards a month do you produce with your machines?

It fluctuates a lot. In one month, for example, we produced about 100 boards with the machine (I think about five thousand components total). There were also months with no production of boards at all.

How were you building these boards before the LumenPnP?

When I joined the company, we placed everything by hand. Using a syringe hooked up to a vacuum pump instead of tweezers helped a lot (we're still using this method).

Next, we bought a "LitePlacer" P'n'P machine. It improved the production immensely. I built some custom strip feeders out of cardboard, holding nearly half a meter of tape. Later, I added the "Blinds Feeder". But I never managed to get the bottom vision working well for passives, so they all were placed directly from tape to board. This led to various alignment issues, and I had to nudge nearly every part (still better than placing by hand - you can't mix up the components).

Later, we started developing our own automatic feeders. Right then, we also discovered the LumenPnP, and we bought one quite early on. Due to other projects getting higher priority, the development of our own feeders slowed down. And, just as Opulo started selling feeders, we got a set. Now, we have forty 8mm and ten 12mm feeders and 47 slots filled on the machine.
 

What has the LumenPnP enabled you to do that you previously couldn't?

Being able to produce small batches of boards quickly and cost-competitively. It cut the production time per board at least by half (in comparison to the older PnP), and looking forward to the V4, it will only get better.

What is the single most important piece of advice for people who are trying to get into PCBA production?

Try using a vacuum syringe instead of tweezers to place components manually - it makes a huge difference! You can pick parts directly from tape, from 0402 up to SOICs, and place them quite easily!

And do not use too much solder paste, especially on components with hidden pads, like QFN, and small-pitched parts. It's pretty hard to remove shorts you can't see.

If using solder paste - use two jars. One is for the virgin paste, and one is for the excess/leftover paste. So you will always have good paste for complicated stuff and very little half-dried-up stuff (that can always be refreshed by adding a little bit of new paste).
  

What's your solder paste of choice? What do you use for a reflow oven?

We use Chip Quik TS391SNL T4 solder paste.

Soldering is done in an "Imdes Solutions" Vapor Phase oven. It solders everything we throw in, from flex PCBs (but a lot of Galden residue is left on them due to the low thermal mass -> better solder Flex Boards with a hot air gun, or, if you have, with a hot plate), to power electronics with a lot of copper and TO92 components next to 0603 passives. The Boards can undergo several solder processes with minimal harm to them (e.g. for double side load).