The term ‘rework’ refers to any work completed after the primary printed circuit board (PCBs) assembly operations are completed. While designing PCBs however, many do not consider how their design choices may impact the future rework of products, even though it is evident that during prototyping, reworks are almost always necessary. Moreover, it is immensely important to remember that you can greatly reduce the amount of potential rework by simply adopting specific design practices.
Today we are looking at 8 different ways to design for rework to inevitably make your life a whole lot easier. Let’s dive into how we can design to ensure reworking your circuit board is not just possible, but simple indeed. Here are 8 steps you can take during the design process…
1) Make Your PCB Size Larger
The prototype rarely needs to be as small as the actual final design, so make it bigger than it needs to be. This will not only allow you to release the design faster by avoiding tricky and intrinsic work, but it’s much easier to rework a larger PCB. Larger PCB allows you to accommodate more PCB test points, if design permits.
A PCB test point is a small wire loop used for test probes to monitor different attributes of your designs through an oscilloscope or multimeter. Test point has the advantage of including time and cost saving by providing easier error detection. On top of that it offers a lower profile like SMT components. When PCB test points are not applicable, think about other test techniques (J-TAG, built in self test, sw auto-diagnostic ..).
2) Use Bigger Components
While it may seem much better to use micro BGA (Ball Grid Array) or QFN (Quad-Flat No-leads) components, you don’t need them, especially not on your prototype. It’s also worth noting that it’s a grueling job to rework parts smaller than a grain of sugar. Moreover, ICs with exposed leads should be preferred over BGA or QFN packages whenever possible for the similar cause.
3) Allow Extra Clearance for Components
Many times, reworking becomes a more complex process than it needs to be whenever components are placed in proximity to each other or in some cases hidden by other components. Rework is much easier when there’s more clearance between components. Think about how an operator can reach the part to substitute based on the space available.
Allowing more space between your components will make localised rework much simpler; especially for BGA, QFN or other packages that exclude exposed leads. If any individual is using reflow heating for rework, additional clearance is always beneficial considering the application of heat that could damage components that are too close. Heat from soldering iron can also distort the nearby components that are in very close proximity.
It goes without saying that such collateral damage starts the chain of new tasks for rework. Despite all this clearance measure, there are some design constraints that are more crucial. For example, sometimes it is necessary to place the components tightly together for the sake of signal integrity. In the following scenarios compromise needs to be made between these factors.
4) Allow Extra Clearance for Tools
Even though all components are placed with sufficient clearance, it is vital to have the clearance for tools, such as soldering irons, to reach all components conveniently. For example, if you need to replace a small passive component of footprint 0603 (and there is a tall tantalum capacitor placed next to it that is coming in the way of your soldering iron, it could disrupt your rework.
It’s not only components that need clearance either. For things such as high-density connectors or even press-fit connectors, clearance is necessary for tools that leverage against the PCB. You may even need larger clearance for tools such as pliers. Do not forget to consider this during your design work.
5) Layout Strapping Resistor and Jumper Options
By designing in strapping resistors, you can pull all your setting pins higher or lower during rework rather simply. You can also accommodate various options in your prototype, for example accumulating extra filter circuits around your power regulators to give yourself multiple options for input power. You could even design a secondary circuit which could be implemented using a simple jumper from one header to another.
6) Use Programmable Parts
By using programmable parts, you allow yourself a little more rework flexibility for the simple fact that inexpensive programmable parts let you rework your designs without putting risk on your hardware. Many times, programmable parts let you make some key changes merely by just adjusting firmware which is far simpler than going through cutting traces or desoldering.
7) Install All Programming Headers
Many PCB designers regret opting out of this one. However, by not doing this has come back to bite a lot of designers on the backside. It is advisable to spend a little extra money and install all programming headers, you will thank us later for that.
8) Replacing Parts
Having to carry out rework is unfortunate but having the spare parts there should you need them makes the process a whole lot easier, so prepare with a spare; it will save you crucial time.