When developping an electronic product a substantial part of the cost comes from electronic parts. PCB usually weight a not very high proportion of the bill of material but still there are some good practices which can be implement to limit cost on manufacturing pcb. Below is a list of few points which directly come to my mind when considering PCB design cost consideration :
Reduce the number of layer on your PCB
Try to optimize PCB thickness and number of layer as much as possible as the more layer you will have in your PCB the more your cost will increase.
Ask yourself : Can I draw my PCB on 4 layers instead of 8 by spending a bit more time to optimize spacing.
Every PCB designer know the importance of placement before routing as it got heavy influence on the needed spacing to route parts on the pcb, hence influentiate spacing requirement.
Avoid blind and buried vias
As you much as you can, you should avoid blind vias and buried vias. Normal “trough hole” vias are manufactured using mechanical drill processing which is the “normal way” to generate via on printed circuit board. If your design include buried or blind via, drilling process can not be used to create those vias, instead laser cutting is used to do so. This process is usually more costly because it require special machines. So, the less buried and blind vias you get on your layout, the more you save on your manufacturing cost.
Avoid tight dimension and tolerances
In the domain of PCB manufacturing, everything which is small and tight requiring more accuracy and precision always involve processes which are more expensive because it require some more efficient machines. For examples, you should particuarly watchout to :
- The smallest via hole diameter dimension
- The smallest distance between two traces
PCB manufacturers usually got limitation with their machine on accuracy so if your dimensions are too smalls, they will need to use more accurate machine which are usually more expensive to use.
In short, you will always pay more and extra for accuracy and precision. So, if you can, try to avoid designing your layout with very high tolerance and very tiny dimensions.
Select PCB materials and finishing properly
PCB finishing have a high influence on pricing due to material use.
Optimize selected material for PCB manufacturing such as finishing or plating of the trace and vias.
Ask yourself: Do you really need a gold plating finishing on those normal pad or can you do without while not compromising quality of your product.
Select components properly
When you design a circuit, some components are highly critical and some are less. Sometimes, a circuit may require a component which the value (e.g resistor or capacitor) to be given with high accuracy and tight tolerances. On the other side, some other components may not be so critical.
On those components which are less critical and influence less your circuit performance, you may easily save a bit some costs if you choose an asian equivalent by swaping this components. Quite often, chip manufacturers will supply reference design with some western components which the cost are usually high. If you open a the BOM of certain reference design at Texas Instruments, you will find out that most of time capacitor and resistors are usually coming from big brands (Vishay, Murata, etc…). Those components are rather basic and since they are, asian manufacturers have no difficulties to produce some equivalent at ultra low cost.
In sort, you can choose asian components for non sensible components for your circuit.
Avoid double side components PCB
Try to get all your components on a single PCB if possible. I have seen in the past some client designing their system on several PCB then linking them together with some connectors or flex.
Unless, you have no choice due to spacing, compliance, radio frequency or thermal constraints, it is always better to avoid double sided component soldering PCBs designs because it involve to perform all the soldering process twice (one on each side of the pcb). One side of the pcb need to be cover with solder paste, then component have to be placed on this same side with a pick and place machine, then the pcb will need to be baked in a reflow oven, and finally components soldering will have to be inspected (normally both with an automatic optical inspection machine and then also manually).
If you have a pcb with components on both side, then you will need to perform this process a second time, have a second set of laser net for solder paste deposition etc..
It also add up complexity (hence risk of quality influencing manufacturing yield) on PCBA manufacturing process because when you have a double sided PCB, one more problem is occurring: gravity. Indeed: you solder SMD components one side and they are maintained by a solidified solder paste which liquefy on temperature rise. When you do the second pass on the other side of the PCB, you will bake again the PCB with side having components being placed in a inverted way upside down on the conveyor of the reflow oven. Hence, under the rise of the temperature, if the process is not perfectly controlled, then components being placed upside down may unsolder due to solder paste liquefaction and gravity.
If not only the process has to be done twice and inflate cost this way, it also indirectly increase unit cost due to PCB defective rejection related to yield.
Don’t place components too close to each other
Unless you are designing a HDI PCB with very high spacing constraint, you better avoid having your components too close to each other. There are several reason to it. First, you will have to respect pick and place tolerances. Second you will have to respect silk screen tolerances. Third, if you reduce the tolerance for placement, then you may need machines more accurate to perform your manufacturing process. If you need more accurate machine, then your process will cost you more. So, if you can avoid to place your component too close to each other, then do it.
Make testing process to be easy and quick
For those who are not used to PCB manufacturing, an essential part of this process is testing being done at the end of the manufacturing process. One of the most easy way to perform PCB testing is by using test point on the PCB by placing some pin (such as pogo pin) on those testing point to test the circuit. The test point directly connect to a certain node in the circuit allowing to connect directly to this node.
Most of time a fixture / jig is created for pin placement so the pins place themselves almost perfectly and automatically on the testing point, after what series of test is performed to verify the functionalities of the PCB. To avoid any problem related to testing, try as much as possible to place those testing point in easily accessible area and if possible grouped together so that your jig pin area is also reduce.
To accelerate the testing process and reduce cost, a testing software should be prepared in advance to perform the necessary tests once the testing pin are connected to the testing points. This software should be simple to use and quick. The more complicated and complex the test, the longer it takes, the more costly it is.
Respect IPC standard
For those who don’t know about it, IPC standard allow components manufacturers, engineers/designers and pcb manufacturers to align on best practice for design, engineering and manufacturing of PCB boards. Those standards have been established by a pool of professionals who have decades of experience in the chip and pcb design and manufacturing. Those people mostly know all the tricks and constantly helps the IPC organization to give guidelines about how to design components, and PCB in the best optimized way.
IPC is for PCB(A) design and manufacturing what is ISO for organization management system. There are plenty of standards which state how PCB should be design and manufacture. So, if during your PCB design phase you align on those guidelines and standard, and if your PCB manufacturer also align on this standard, then the failure and quality issue occurrences will be lower, hence the yield higher, hence your price lower.
If you are employing a designer or engineering company to design your PCB, I invite you to ask them which kind of standard do they use to design their PCB. You should do the same for PCB manufacturers. If they don’t give you quickly an “IPC related” answer, you should better avoid working with them because it will increase the chances to get trouble on design or manufacturing phase due to non standardization.
Get your components being delivered in tray or roll
Components can be supplied by components manufacturers in several different ways. Take the example of SMD switch. You can buy them in bulk bag or you can buy them in tray.
If you want to reduce cost and lead time, you will need to use a pick and place machine to place components on your PCB in an automatic way. Those machines use roll (for small components) and tray (for bigger flat components) as feeders. Typically for roll, the machine will unroll the roll to pick the component directly from the roll, for tray packaging a sucking device will move on X and Y axis to pick the component
If you buy components in bags packaging, it will not fit the pick and place machine requirement so you will not be able to use a pick and place machine to place components. Hence, it will need to be done manually, which means: slow process, non accurate, random and non repeatable placement with risk on quality. It will increase processing time, will reduce yield and adequately will influence your cost in the wrong direction.
So, you should always buy your components in roll or tray and never in bulk unless you have a very specific reason to do so.
Make sure components are cleaned and not rusted
Sometimes, you may send your components to your PCB Assembler so they can process your PCB assembling using the parts your purchased. I usually do so, so that I am sure the parts which are used on my PCBA are the one I have decided for and not some decided by the manufacturer.
Yet, when between the time when they receive those components and the time when they assembly them on PCB, sometimes several days, weeks or even months may occur. In China, the air is highly humid and temperature is usually warm. Components are usually sealed in their roll but some of them are stored in tray where sealing may not be optimized or sometimes after a first batch being done, some inventory remain, are stored for the next production batch. In this case, considering that components got connectors in metal it may happen that those connectors start to get rusted, hence making pad to component legs contact on soldering unefficient. In this case your components will become useless and you will have wasted a lot of money.
Hence, when choosing your PCB manufacturer, perform a quick supplier audit to verify how do they store your components. I have seen in the past, some PCB assemblers fully aware of constraints related to humidity and temperature, in this case they may store some particular components in some chamber where they control temperature and humidity
Make sure solder paste quality
Solder paste is as an essential element of PCBA manufacturing. For those not aware of what it is, the solder paste is a material which is deposited on the PCB pads using a net. When this paste is heated up, the paste transform into liquid which is used to solder component “legs” on PCB pads.
There are different type of grade of solder paste. Some of them contain lead and you better avoid them for compliance constraints. Some of them contain mix of tin and lead in different proportion. The more tin you have the better the connection between the component and the PCB. To optimize your PCB cost you can play a bit on the selection of this solder paste (but not too much!).
Avoid through hole components
If you choose component which are trough hole types, then placement of those components on the PCB will have to be done by hand.
Indeed, today there are no machine doing placement of trough hole components in an automated way. If placement is done by hand, it will increase the cost of your PCB assembling and will also increase the risk of defects. In order to keep low cost, never use trough hole components unless you have a serious reason to do so (usually for easy maintenance reasons).
Avoid exotic components
If you plan to use some “exotic” component which are difficult to procure in China then you might need to import them first. If you need to import them, then probably you will have to pay some extra taxes on them and it will inflate your bill of material.
On the top of it, if you use some exotic components you may need to plan much well in advance your procurement strategy to avoid lack of supply.
Did I forgot anything ?
Leave a Reply