Fabricating circuit boards is a complex process that requires you to factor in several variables to get the formula right. One of the defects that might arise is PCB delamination. This issue usually occurs due to manufacturing errors, but there are ways to prevent it. We will look closely at this defect to explain its causes, prevention measures, and repair steps. Read on to learn more!
What is PCB Delamination?
Delamination defines the physical separation of circuit board layers and can occur in inner or surface layers. The splitting can cause malfunctions in the internal layers that are difficult to pinpoint without thorough examination.
PCB inner layers
If viewed on an assembled printed circuit board or a bare one, delaminations might appear as broad discolored or bubbling regions.
Blistering vs. Measling
Delamination has two related forms. Blistering is the partial separation that causes bubbles or gaps that look like blisters. The damage usually occurs in the production process.
On the other hand, measling refers to white spots on the PCB weave interior that indicate element destruction on the board. Small measling is tolerable, provided:
- It is not very frequent
- Does not bridge conductors and soldering eyes
Common causes of measling include errors in production and mechanical stress.
Causes of PCB Delamination
The two primary factors that lead to delamination include the following.
Repeated thermal stress before and after the assembly process can cause delamination, especially if the heat exceeds the glass transition temperature.
Manufacturers can prevent delamination by examining the wave soldering and reflow profile parameters to ensure the PCB base materials will not encounter excessive stress.
Circuit boards in an assembly line before wave soldering
Thermal-stress delamination might start in the interior layers without creating blisters or causing cracks on the surface layer. The manufacturer should use high-Tg board base materials if the board undergoes multiple soldering cycles, large thermal excursions later, or both.
Moisture buildup in the PCB base layers is one of the most typical causes of delaminations. This moisture can contribute to CAF (Conductive Anodic Filamentation), where the water gets into electrochemical reactions that create tiny filaments. These filaments can bridge conductors, causing short circuits.
And this moisture will turn into steam when temperatures elevate during the processing steps later. The reflow soldering process, for instance, occurs at temperatures above 200°C. Such heat levels are well above the boiling temperature of the water and will convert the moisture into steam.
A PCB in a reflow oven machine to heat up the solder paste
The pressure from this steam will interfere with curing and board pressing, ripping some sections apart. These separated parts or blisters might show immediately or later during subsequent thermal processing steps or large thermal excursions when the printed circuit board is in use.
How To Prevent PCB Delamination
It is possible to prevent measling and delamination in the PCB manufacturing process by pre-baking the PCB base layers before fabrication and assembly. This step should evaporate all the moisture content.
Also, ensuring resin controls and running the reflow soldering process at the right temperature can prevent delamination.
Circuit board laminates tend to absorb moisture under improper humid storage conditions because the base materials are hygroscopic. So you can prevent delamination by storing the board in dry places. Additionally, you need to ensure the quality of the oxide layer in the board's inner layers is top-notch.
A water-damaged PCB
There's not much you can do as a designer to prevent this issue. Most of the responsibility falls in the hands of the manufacturer and assembler. So you need to employ the services of a high-quality PCB manufacturer. OurPCB has the required technical expertise & experience and high-quality machines to deliver delamination-free PCBs for your project.
Delamination Measurement Tests
Manufacturers usually use the time to delamination test for testing the base material performance. This time test measures how long the copper and resin or resin and reinforcement takes to separate/delaminate.
The test uses TMA (Thermomechanical Analyzer) equipment to elevate the temperature of a sample PCB to a specified level, then measure how long it takes for failure to occur.
Typical temperatures used for these tests are 260°C and 280°C, with the former considered more accurate and relevant in lead-free assemblies. The glass transition temperature plays a vital role in this test. Most low-Tg FR-4 materials exhibit higher times to delaminate than high-Tg FR-4 materials.
An FR-4 material PCB
Delamination Repair Steps
You can implement these repair steps to rectify a delamination problem. But first, you need the following items.
- Abrasives, ball mills, cutting tools
- Circuit bond epoxy
- Micro drill system
- Mixing picks
- Clean the blister surface using wipes
- Drill at least two holes into the delamination blister using the ball mill and micro drill. The holes should be opposite each other and around the blister's perimeter. Also, they should be clear of any components or circuitry. Brush off the loose material after drilling.
An electric micro drill for drilling PCBs
- Caution: Don't drill too deep to expose the inner planes or circuits. And keep in mind abrasive operations can generate static charges.
- Bake the circuit board in the oven to eliminate any moisture content. Don't let it cool before injecting the epoxy because moisture might condense and get trapped inside again.
- Caution: Some electronic components are sensitive to high temperatures. Don't take the heat too high.
- Pour the epoxy into the cartridge, then inject it into one of the drilled holes. The heat in the PCB should help distribute the epoxy, drawing it into the void area to fill the space.
Blue epoxy resin bottles
- Apply light pressure on the board if the blister does not get filled. Begin at the fill hole and proceed to the vent hole slowly. Alternatively, you can apply a vacuum to the vent hole to pull the epoxy and fill the void.
- Cure the epoxy at room temperature for 24 hours or at 74°C (165°F) for one hour.
- Scrape off any excess epoxy using a scraper or knife. Apply a thin coat if required to seal the scrapped areas.
After drying, do a visual examination to check the color and texture. Also, do electrical tests on conductors around the repaired area to see if everything works.
In summary, poor manufacturing processes are the leading causes of PCB delamination. Although there is a way to repair the issue, it is better to prevent it before it occurs. So look for high-quality fabricators like OurPCB to build you the boards for your project. Contact us with your layout files, and we'll give you a free quote before getting to work.