How Are You Making PCBs? A Quick Overview of PCB Production
I have a specialty breakfast that I make for our friends when we are all camping together. A word about this particular dish has been passed around so much that no one else wants to make it; they all wait for me to pull out the camp stove and griddle in order to start cooking. The problem is that during the long winter between summer camping trips, I will often forget just exactly what I need to do in order to create my signature meal. It has been embarrassing to me on more than one occasion when I have had to admit that I don’t remember what goes into it when asked for the recipe.
Forgetting how to create a simple breakfast around the campfire is actually a little funny, but forgetting some of the basics about how are you making PCBs can really be embarrassing. Sure, you could go and research the whole thing, but let’s take a moment to hit some of the highlights here. Maybe that will be enough refresh some of those thoughts that are on the tip of your tongue that you just can’t quite put into words.
How Are You Making PCBs? The Best Design Tools are the Place to Start
When you want to design a printed circuit board, you’ve got to start right; with the best PCB design tools that you can find. Sure there are lots of free or less expensive tools out there that will get you through a layout. The problem though is that as the complexity of your designs continues to increase, eventually those simple tools will let you down. Do yourself a favor then and make sure that the tools you use can handle all of the needs that you are going to throw at them, both now and in the future.
You’ll want to take steady and consistent notes of your design process and necessities.
Printed Circuit Board Fabrication and More
Circuit boards are made from a core material which is usually a woven glass epoxy base called FR4. This core material will have copper on one or both sides and the copper will be covered with a light-sensitive material known as a photoresist. A reverse image of the copper circuitry that you provided will be used to cover the areas of the photoresist that are not desired to be exposed.
The board is now exposed to an intense ultraviolet light and the areas of photoresist left uncovered by the reverse image of circuitry will become hardened by the light. Once the remaining soft photoresist is washed off, the board now has the areas of copper circuitry covered with photoresist. At this point, the board is processed through chemicals to remove the areas of copper not covered by photo resist leaving only the copper circuitry that was depicted in your design files.
From here the different board layers are composited together. The core and copper layers are compressed together with layers of pre-impregnated bonding sheets known as “PrePreg” to glue the layers together as well as provide insulation between the layers of copper. At this point holes for thru-hole parts and vias will be drilled, solder mask will be applied, and board information and reference designators will be silk-screened onto the exterior layers.
This is a simple description of the standard process of fabricating a PCB where the copper metal is subtracted from the board. There are also other fabrication methods for hybrid designs or “printed electronics” where metal substances are printed onto the core substrate instead of etched off.
Testing your circuit is invaluable to ensure proper fabrication and assembly
Finish the Job; PCB Assembly and Test
After the bare boards are fabricated, they now need to be assembled. Automated pick and place machines will place the parts on the board using data provided by your design files. The thru-hole parts will be soldered in place when the board is run through the wave soldering process while the surface mount parts with solder paste on their pads will go through solder reflow. When the assembly is complete, the board will be ready to be tested through either in-circuit testing (ICT) or other test processes.
The key to the assembly process is in the quality of documentation that you are able to provide from your PCB design tools. The PCB assembly shop needs to know exactly what parts to work with for both ordering and assembling your board. By ensuring that they have the most up-to-date information in output documentation, you will be able to guarantee that the assembly process will go through without any problems.
If you’re looking for the proper PCB design software that can make your designs come true with the least amount of trouble, then Cadence’s suite of layout and analysis tools will assuredly make your job the easiest. OrCAD PCB Designer has everything you need to get your boards checked, routed, and verified.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.