Designing for Selective Robotic Conformal Coating Processing: Rule 13 “Sticking coatings to non stick silicones is a pain”
Applying silicone RTVs to circuit boards to provide support to components for long term reliability is fine. Just don’t do it before you apply a conformal coating to the surface unless the conformal coating itself is a silicone. Acrylic and urethane coatings do not stick to silicone. So, don’t try unless you want defects appearing.
Rule 13
If you call out silicone staking materials for ruggedisation purposes, use a silicone conformal coating. If you don’t want to use a silicone conformal coating, then use a urethane or epoxy staking compound.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 12 “Coating 3D components is hard work. Why do it?”
When a circuit board surface looks like a scene from a cityscape and is highly 3D in nature, choosing to coat the sides of components is a really difficult process. You will need at least 5 axes of rotation, the process will slow down, quality really goes down and it looks awful cosmetically. If you don’t need it, don’t do it.
Rule 12
Make coating component packages optional. Coating the sides of a 3D device is difficult, especially since the coating is subject to gravity, as well as de-wetting due to mould release agents used in the component fabrication. The plastic or metal package mouldings are almost certainly more resistant to humidity or other forms of water than any conformal coating.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 11 “Why do you want to coat the edge of a circuit board”
Conformal coating works by protecting the components and stopping conduction through leakage between leads and devices. Most of the time the edge of the circuit board does not need to be coated. So, why specify that it should be?
Rule 11
Make coating the edge of a PCB optional – it is tricky and messy, especially if there is no frame or breakout around the board, and is of questionable efficacy in improving coating or reliability performance.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 10 “Treat connectors with respect!”
Conformal coating and connectors are the ultimate problem for processing with a spray valve or gun. Any coating close to a connector could wick (suck up into) a connector very easily and ruin the component. Therefore, a strategy for handling coating around connectors is required.
Rule 10
Use conformal coating gel around connectors if you want to get close to the connector with the material. Conformal coating materials will flow freely into unsealed connectors and wick up connector leads.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 9 “A flat board is a happy conformal coating process”
Many printed circuit boards can become warped in the manufacturing process. Or, they can bend in the conformal coating process if not adequately supported. This means that the surface is not even for the valves to travel across. For processes where the valves are running very close to the surface of the board this can be critical and lead to defects.
Rule 9
The board should be flat and sufficiently rigid to prevent sagging during dispensing or curing, otherwise coatings may flow and pool in unexpected fashions. In particular, heavy boards may need to be palletized to provide sufficient rigidity.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 8 “Biscuit layout can be critical. Get it right”
When laying out multiple PCB biscuit designs , this can be a real source of problems and make the process very inefficient.
Rule 8
When coating multiple PCBs in a biscuit configuration, ensure you seek input from production engineers regarding orientation to optimise robot path and valve operation. Having to stop and start often and/or change dispense height reduces your throughput massively and the coating can be deposited poorly.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
Designing for Selective Robotic Conformal Coating Processing: Rule 7 “Add tooling holes for the PCB if the board is not a standard shape to be supported on the fixture or conveyor”
Many PCBs can be irregular in shape or have components very close to the edge. This can make it very difficult to support the circuit board on a fixture or even worse on a moving conveyor. So, this may mean it is difficult to get the position to be repeatable. If the position is unrepeatable then the coating will go where it is not wanted.
Rule 7
Add tooling holes for the PCB if the board is not a standard shape to be supported on the fixture or conveyor.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
What is a needle dispense valve on a conformal coating selective robotic system?
This style of valve can be used to dispense more or less any material, from a no-flow gel to a water-thin consistency and the length of the needle used can help to ensure access between very tall components for example.
Dispensing from a conformal coating selective robot
To find out more about this and other valves for conformal coating application click Choosing the Right Valve for a Selective Robotic Conformal Coating Application Process
Designing for Selective Robotic Conformal Coating Processing: Rule 5 “Do not use a conformal coating as an underfill”
Under fills are used to fill the gap under components like flip chip components. The materials are specifically designed to match the coefficient of thermal expansion (CTE) of the device on the board so that any CTE change does not mean the component pops off the board or gets damaged. Conformal coatings are not designed for this process and CTE mismatch can lead to severe damage of devices such as BGAs.
Rule 5
Do not specify the use of conformal coating as an under fill EVER. If a device needs to be under filled, specify a formulated under fill. Or, be prepared to find the component lifting off the PCB in the long term.
The Rules
The Rules for Selective Conformal Coating are straightforward. Follow them and you can save money and time in your application process. However, if the Rules are not followed, the resultant circuit board design can challenge even the most sophisticated conformal coating system and its operator to achieve the finish desired.
Click Designing Circuit Boards for Selective Robotic Conformal Coating for further Rules.
What is a contactless dipensing valve and how does it work with my selective robotic conformal coating system?
As the name implies, these valves typically operate between 2-10mm from the surface onto which they are dispensing and can apply very small dots or well defined lines and can be used to coat critical areas or discrete components. These types of valves generally work best with materials with some degree of thixotropy and medium apparent viscosities. These valves do rely on unhindered access to the coating area and are most suitable for SMT technology.
Contactless dispensing from a conformal coating robot
To find out more about this and other valves for conformal coating application click Choosing the Right Valve for a Selective Robotic Conformal Coating Application Process
Conformal Coating 