PCB Manufacturing Options Explained
Once you generate your manufacturing files- Gerber, nc drill, (pick and place if you are having them do assembly) you will need to choose a pcb manufacture. Here at Victory Electronics™, we highly suggest going with a USA manufacture for reasons specifically related to supporting our country, but you may choose as desired. One thing to note is that the manufactures in China and Taiwan will typically be a little cheaper since their labor rates are much lower than the USA’s. Quality and cost are not always synonymous, however such factors are usually more closely related when speaking of pcb manufacturing comparisons within the same country. For example you may come across some cheap manufactures in China that are mainly dealing in prototype quick turns, and a more expensive manufacture in China will likely be better quality. A way to check this is to see if they offer a free DFM check(design for manufacturability), and also check out their “capabilities section”. I have come across some manufactures who are cheap and don’t DFM check, and will manufacture a specified design which is not even within their “capabilities”. This is not good obviously, so if the manufacture doesn’t have a DFM check please be sure to take it upon yourself to check and make sure your design rules are within the manufactures capabilities/tolerances. As long as they are, and they have a good reputation, you should generally be okay.
So typical PCB options:
First your Pcb type, FR4, aluminum, copper etc.
FR4 is standard for 99% of designs and is made of woven fiberglass and epoxy. The FR4 rating- “FR” stands for “flame retardant” and these have different ratings which deal with how much heat the pcb can handle. Usually standard is perfectly fine for the vast majority of designs however you might want to go with a higher rating if you are doing something like automotive, aerospace, military. They should list the temperature specifications next to the rating.
This is already predefined in your gerbers and is the total copper layer count. Select what is in your design. Typically this will be in even numbers except for single Layer which is not very common. Most common is 2 layer for basic PCB’s, but if you are for instance designing a computer motherboard or something complex like that, you will need 6 or more layers and cost will go up proportionately with layer count. In most cases odd numbers aren’t even listed here and they may end up charging you even more for that if they can even do it.
Board size dimensions
These are already defined in your gerber files however they often ask this since it’s needed for their “instant quote” calculators.
Please pay attention to the Unit of measure section. Some are in inches and some mm, make sure to note correct one.
Simply select how many boards you want manufactured. If you are just getting a few boards made and you want your manufacture to also do the assembly you will end up paying an outrageous amount. Example: Say you want 5 boards with full turn key assembly. The cost of this may be only slightly less than say 50. The cost of the boards will go down significantly when the quantity goes up, but the assembly fee remains similar regardless of how many boards they are going to assemble. This is because they have to setup all the components on tape and reel , load the pick and place machines etc.. it’s the same amount of setup regardless.
So you can potentially save thousands if you don’t mind or are capable of doing assembly yourself on a prototype run. Although not necessary, if you are going this route you could ask them to add a laser cut steel stencil to your order. This is made according to your gerber files and the stencil will just line up with all your pads on the board. This can help assist you in applying solderpaste to only those areas and have it be uniform amounts throughout evenly and quickly. This is certainly not necessary though. For small prototypes I have at times just dabbed them solder paste on there in amounts that work, but that does require a certain amount of skill and often takes longer to apply as well.
This is how thick the finished board will be. Standard is 1.6mm but as your layer count goes up, eventually the thickness will have to as well. Each layer requires a certain amount of space within the board and so much tolerance is needed between said layers. You can even get down to .6mm thickness typically with a small layer count but I only suggest doing so if absolutely necessary since it will also make the boards more prone to flex. For example, in the pursuit of thin devices newer MacBooks and some other laptop boards have gone down to 0.6mm thickness and these boards are 6 layers or more. In this case they are really pushing the limits of what is possible and it can sacrifice reliability.
Side note: one thing to note if you are in Altium or your pcb design software, most have the ability to generate step file to assist you in creating an enclosure for the board. Be sure to specify that accurately to what you manufacture it at otherwise you will have an enclosure that matches your step file perfectly but not your manufactured board.
This is the color of the lacquer like solder resist that goes over top of the copper to protect it and coat your board. You can get different colors but a lot of manufactures will charge more for different colors so be sure to check that. Standard is usually green.
This is the color of the writing on your board. For instance if you have a logo, component designators, footprint outlines, etc.
Finished copper weight
Most boards are standard 1oz copper which is 35 microns (uM) however you may want a heavier copper weight in cases where you want to minimize the resistance and inductance. For example say you have a high current amplifier- it would benefit from a heavier copper. Just like using a thicker wire also lowers the wires resistance it’s the same as a heavier copper weight. To learn more about reducing inductance in pcb design read here- https://givemebass.com/advanced-decoupling-and-bypass-techniques-for-high-quality-audio-performance/
One thing to keep in mind is that it’s more difficult to manufacture within tight tolerances when using a heavier copper layer. This means things which have very small spacing between them may have difficulty being made into a higher copper board so it’s always best to check with the manufacture to make sure their capabilities can handle those tolerances.
Surface finish -This is how they coat the exposed copper pads on the board when it’s manufactured.
“HASL” or hot air solder leveling is typically available with leaded solder but for ROHS compliance you can get lead free which will just have tin, nickel, silver or whatever else they put in the solder to replace the lead. “HASL” consists of cleaning the board and putting it into a solder bath which puts small amount of solder coating on the pads, then they will blow off the excess solder. Sometimes the ultra thin coating that goes on there can be a little uneven. Since it can’t have a perfectly flat planar finish if you are doing a BGA(ball grid array) for instance you may want to go with a different surface finish that can have a more level surface.
“ENIG” or electroless nickel immersion gold consists of cleaning the board and then putting a small thin layer of nickel over the exposed copper pads and then with a gold plating over top of that. Some manufactures will try to sell you on this especially if you have a lot of plated through hole components and that’s generally because “HASL” can be a bit more difficult to apply for these but HASL can still work just fine. ENIG does create a flat planar surface but if you intend to do a lot of rework it can wear out pretty fast. ENIG also sometimes develops “black pad” which is where the nickel reacts with gold and causes corrosion on the pad. It can cause cracked joints and poor solderability. It’s pretty rare if applied properly though and there’s a big debate on what causes this but basically a lot can have to do with contaminants that are present when they apply the nickel and the gold .
Immersion Silver – same thing as ENIG but with a silver coating over the exposed copper. One bad thing is that it can tarnish when exposed to air so if you wanted to have these boards made a long time before assembly it may not be a good option for you, if you do get it done I recommend you communicate with your manufacture , sometimes they can put an anti tarnish coating on the boards or they can vacuum seal them in a package if you don’t want the assembly immediately
“ENIPEG” or electroless nickel electroless palladium emmersion gold is where they clean the board and then put a layer of nickel, then palladium, then gold. This can help prevent the “black pad” syndrome which sometimes happens with ENIG. This also provides a very flat surface, is best for BGA and allows for more rework to be done. Also ROHS compliant.
“OSP” or organic solderability preservatives is another ROHS compliant option. Some countries may require eliminating a lot of hazardous substances so this is a more eco friendly option. Can’t think of any reason to use it other than if you you’re legally
On outside of pcb they can put like a through hole ring. This will be defined in your gerbers and may be part of a component footprint.
If you have BGA devices in your design then you may want an X-ray check. This can check to see if the solder balls are properly soldered and not touching. However X-ray checks can also be a form of quality control for the PCB
tolerances in general.
If you are getting assembly do you need one or both sides done?
This will only be necessary if you are also getting an assembly service done since a conformal coat spray is a last step finish that can be applied over top of the assembled components and pcb. This step is optional and not needed. However if you want an additional layer of protection on your boards to protect them from the elements you can get conformal coat. There are a few different types with acrylic being most common. It has a high dielectric strength, is fast to apply, and offers a basic level of protection. This is usually what I’d recommend for most general and non extreme cases and is what we apply to the amplifier we designed for “the only” https://givemebass.com/product/the-only/ It also is something that can be applied later on since it’s in convenient spray bottles, or can be brushed on. It’s easy to remove with isopropyl alcohol and so makes rework easy to do.
The next type is parylene which is a permanent type of conformal coat that has high dielectric strength, offers maximum protection, is very expensive, and makes rework nearly impossible. It’s one the best option though for boards that will be exposed to very harsh conditions.
There are various other types of conformal
Coat such as epoxy or silicone resins but these vary on formulation a lot and are not too common.
Gold fingers- these are the fingers on boards that will be plugging into something. For example, pci express WiFi cards, ssd, mxm graphic cards, etc.
The main options here are “tented” or “non tented”. Tented just means covered with soldermask and non tented would be without the soldermask. If you have a lot of vias in close proximity to other vias or pads you can sometimes get solder bridge between pad and via if not tented which is why I prefer to get them tented. However if things are not in close proximity like that you can get them non tented if you want to. A lot of times they will just manufacture according to what your gerbers say but sometimes they will ask you and if you select differently they may edit your gerbers to match your selection so be careful here.