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Top 10 Quality Issues and Solutions for PCB Products

Top 10 Quality Issues and Solutions for PCB Products - ELEPCB
Table of Contents

There are many control points throughout the entire production process. With the slightest carelessness, the board may be damaged. Quality issues with PCBs are inevitable and headache-inducing because even a single defective piece can render most components unusable. In addition to the aforementioned problems, there are some risks that are worth additional attention. We have collected and organized 10 common issues, with some experienced-based solutions shared below:

✅ Delamination

Delamination is a critical quality issue that can significantly impact the structural integrity and performance of PCB products. It refers to the separation or detachment of different layers within a PCB, resulting in reduced electrical conductivity, compromised signal integrity, and potential failure of the circuit board.

Delamination can occur due to various factors. The reasons for its occurrence may be roughly as follows:
(1) Improper material selection
(2) Inadequate lamination processes
(3) Exposure to excessive heat or moisture during manufacturing or operation
(4) Design selection and copper surface distribution is not good.
Moisture problems are more likely to occur, even if the choice of good packaging, factories also have constant temperature and humidity warehouse, but the transportation and temporary storage process cannot be controlled. I had the “honor” to visit a bonded warehouse, temperature and humidity management is not expected, the roof is still leaking, the box is directly in the water.

However, moisture can still be dealt with, vacuum conductive bags or aluminum foil bags can be good protection against water vapor intrusion, while the bag is required to put the humidity indicator card. If the humidity card is found to exceed the standard before use, baking before going online can usually solve the problem, baking conditions are usually 120℃, 4H.

In order to minimize the occurrence of such problems, special attention needs to be paid to the PCB supplier’s management of the corresponding processes and layering reliability tests. Take the thermal stress test in the reliability test as an example. A good factory’s passing standard requires that there be no delamination more than 5 times, and it will be confirmed at the sample stage and each cycle of mass production, while an ordinary factory’s passing standard may only be 2 times. The IR test of simulated placement can also prevent the leakage of defective products, which is a must for excellent PCB factories.

Of course PCB design can also bring the hidden danger of delamination. For example, the choice of plate Tg, sometimes there is no requirement, that PCB factory in order to save costs, certainly choose ordinary Tg materials, which pocesses poor temperature resistance. In an era when lead-free has become the mainstream, it is safer to choose products with high Tg above 145°C. In addition, large open copper surfaces and too dense buried via areas are also hidden dangers of PCB delamination and need to be avoided during pcb design.

✅ Poor Solderability

Poor solderability refers to a condition where the solder does not properly adhere to the intended areas on a PCB, resulting in weak or unreliable solder joints. Possible issues are:

– ENIG Black Pad
ENIG Black Pad, also known as Electroless Nickel Immersion Gold Black Pad, refers to a specific defect that can occur during the surface finishing process of printed circuit boards (PCBs). It is a condition where the gold-plated surface exhibits a black or dark discoloration, rendering it visually unappealing and potentially compromising the functionality and reliability of the PCB.

Black Pad is believed to be caused by a phenomenon known as nickel corrosion or nickel phosphorus depletion. It occurs when the nickel layer in the ENIG finish becomes brittle, porous, or non-adherent due to inadequate processing or the presence of impurities. As a result, the gold layer on top of the nickel may appear black or dark, indicating poor solderability and reduced reliability.

Quality Issue - ENIG Black Pad - ELEPCB

Preventing and mitigating Black Pad requires careful attention to the entire ENIG surface finishing process. Some measures that can be taken to minimize the occurrence of Black Pad include:
(1) Proper Process Control: Maintaining strict control over the ENIG process parameters, such as solution composition, temperature, and deposition time, can help ensure a consistent and reliable surface finish.
(2) Surface Preparation: Thoroughly cleaning and preparing the PCB surface before applying the ENIG finish is crucial. This includes effective removal of any contaminants, oxide layers, or surface irregularities that may compromise the adhesion and quality of the ENIG finish.
(3) High-Quality Materials: Using high-quality electroless nickel and immersion gold solutions, free from impurities or contaminants, can contribute to a more robust and reliable ENIG finish.
(4) Thorough Inspection and Testing: Regular inspection and testing of the ENIG finish, including visual examination, solderability testing, and reliability testing, can help identify any potential Black Pad issues early on and allow for corrective actions to be taken.

Solder mask scum
Solder mask scum, also known as solder mask residue or solder mask contamination, refers to the presence of unwanted material or residue on the solder mask surface of a printed circuit board (PCB). It appears as a thin layer or spots of foreign substances, such as dust, oils, or other contaminants, which can negatively impact the functionality, reliability, and aesthetics of the PCB.

Solutions:
(1) Thorough Cleaning: Implementing effective cleaning processes after critical manufacturing steps, such as soldering or surface finishing, to remove flux residues or other contaminants from the PCB surface. This can be achieved through techniques like ultrasonic cleaning, solvent cleaning, or automated cleaning systems.
(2) Controlled Curing Process: Ensuring the proper curing and hardening of the solder mask material according to the manufacturer’s recommendations and process specifications can help prevent incomplete curing and the formation of scum.

✅ PCB Warping

PCB board warping refers to the condition where a printed circuit board (PCB) exhibits a non-flat or deformed shape. Instead of being flat and rigid, the PCB may have a noticeable bend, twist, or curvature. This warping can occur during the manufacturing process or as a result of environmental factors or stress applied to the PCB.

PCB board warping can occur due to a range of contributing factors.
(1) Inconsistencies in the manufacturing process, such as improper material selection, inadequate temperature control during lamination or soldering, and uneven distribution of copper layers, can lead to differential expansion or contraction and result in PCB warping.
(2) Thermal stress experienced during soldering processes, such as reflow soldering or wave soldering, can induce thermal gradients across the PCB, causing uneven expansion or contraction and contributing to warping.
(3) Moisture absorption, often due to improper storage or sealing, can cause the PCB material to expand unevenly and lead to warping.
(4) Mechanical stress from mishandling during assembly, improper mounting or installation, or excessive bending or flexing can introduce stress and deform the PCB.

quality issue - pcb warping - elepcb

The consequences of PCB board warping can include:
Component Misalignment: Warping can result in misalignment of components, making it difficult to mount or solder components accurately. This can lead to poor solder joints, intermittent connections, or even component damage.
Electrical Shorts or Opens: Warping can cause unintended contact or separation between conductive traces, leading to electrical shorts or opens. This can result in circuit malfunctions, loss of signal integrity, or complete circuit failure.
Mechanical Fit Issues: Warped PCBs may not fit properly within their intended enclosures or mechanical assemblies, impacting the overall functionality and reliability of the final product.

✅ Exposed Copper

Exposed copper that is unintended or outside of the designated areas can result in several problems. It can lead to unintended electrical connections, short circuits, or inadequate isolation between different circuit elements. Exposed copper areas that lack proper solder mask coverage are susceptible to oxidation, which can affect the solderability and long-term reliability of the PCB.

To clarify, the deliberate design of exposed copper is essential for the operation of the PCB, but defects related to exposed copper arise when there are deviations from the intended design or unintended exposure occur in areas where it should be properly covered or controlled.

Exposed copper issues are the issues that most test the PCB factory’s management system and execution capabilities. This problem is not serious, but it does cause quality concerns. Any PCB factory that seriously promotes the project has significantly improved the DPPM delivered.

✅ Poor Impedance

Poor impedance refers to a condition in which the impedance of a transmission line or an electrical circuit deviates from the desired or specified value. Impedance is a measure of the opposition to the flow of electrical current in a circuit and is typically characterized by resistance, inductance, and capacitance. This can lead to various issues and consequences, including:
(1) Signal Integrity Problems: Impedance mismatch can cause signal reflections and distortions, leading to signal degradation, loss of signal integrity, and reduced overall performance of the circuit. It can result in data errors, increased signal attenuation, and decreased signal quality.
(2) Power Delivery Issues: Inadequate impedance matching can affect the transmission of power in the circuit. It can lead to power losses, inefficient power transfer, and voltage drops, impacting the functionality of the circuit or system.
(3) Electromagnetic Interference (EMI): Poor impedance can contribute to increased electromagnetic interference effects. It can result in signal crosstalk between traces, susceptibility to noise, and radiation of electromagnetic waves, leading to EMI-related problems and reduced reliability.
(4) Timing and Synchronization Errors: Impedance mismatch can affect the timing and synchronization of signals in the circuit. It can lead to signal skew, propagation delays, and timing errors, which are particularly critical in high-speed digital circuits or communication systems.

quality issue - poor impedance - elepcb

The impedance of PCB is an important indicator related to the radio frequency performance of mobile phone boards. A common problem is that the impedance difference between PCB batches is relatively large. Since impedance test strips are usually made on the edge of the large PCB board and are not shipped with the board, the supplier can be asked to pay the batch of impedance strips and test reports for reference each time it is shipped, and it is also required to provide Comparative data of board edge wire diameter and board internal wire diameter.

✅ BGA Solder Voids

BGA solder voids refer to the presence of empty spaces or gaps within the solder joints of a ball grid array (BGA) component. A BGA is a type of surface-mount integrated circuit package that uses an array of solder balls on the underside of the package to establish electrical connections with the PCB.

quality issue - bga solder void - elepcb
BGA gas voids 1

This type of failure may occur due to residual liquid or impurities in the PCB holes that vaporize after high temperature, or poor laser hole pattern on the BGA pad. The voids appear as trapped air or gas pockets within the solder material. These voids can vary in size, shape, and distribution, ranging from small isolated voids to large interconnected voids.
BGA solder voids may cause malfunction of the main chip and may not be discovered during testing, so the hidden risk is high. Therefore, many patch factories now conduct X-RAY inspection after mounting the parts. Therefore, many HDI boards now require electroplating to fill holes or semi-fill holes to avoid this problem.

✅ Solder Mask Blistering

Solder mask blistering or falling off refers to a condition where the protective solder mask layer on a printed circuit board (PCB) exhibits abnormalities such as bubbles, blisters, or peeling, and in severe cases, the solder mask layer detaches from the PCB surface.

The solder mask is a thin layer of polymer material applied to the PCB to protect the underlying copper traces and prevent solder bridging during the soldering process. It also provides insulation and helps protect the PCB from environmental factors such as moisture, dust, and chemical contaminants.

Such problems are usually caused by abnormalities in the control of the PCB soldering mask process, or the selection of unsuitable solder mask ink (cheap, non-gold ink, not suitable for mounting flux), or the temperature of the patch is too high. To prevent batch problems from occurring, PCB suppliers need to formulate corresponding reliability testing requirements and control them at different stages.

✅ Via Fill Material Defects

Via fill material, also known as a via filling compound or via fill resin, is a non-conductive material used to fill vias on a printed circuit board (PCB). Via fill material defects refer to abnormalities or issues associated with the material used to fill vias on a printed circuit board (PCB). Via filling is a process where non-conductive material, such as epoxy or resin-based compounds, is injected or applied to fill the vias, isolating them from other conductive layers.

This is mainly caused by the PCB factory’s lack of technical capabilities or simplified processes. They are manifested as incomplete via filling and exposed or false copper exposure in the annular rings. It may cause problems such as insufficient solder volume, short circuit with the patch or assembly device, and residual impurities in the vias. This problem can be discovered during appearance inspection, so it can be controlled during incoming material inspection, requiring the PCB factory to improve it.

Via fill material defects can have various implications on the performance, reliability, and functionality of the PCB. They can affect signal integrity, power delivery, mechanical stability, or resistance to environmental factors such as moisture, temperature, or vibration.

✅ Poor Dimensions

PCB dimensional issues refer to problems or deviations in the physical dimensions and measurements of a printed circuit board. These issues involve variations or discrepancies in the size, shape, or positioning of the PCB and its components, which can impact the functionality, assembly, and reliability of the board.

There are many possible reasons for poor dimensions. The PCB production process is prone to expansion and contraction. The supplier has adjusted the drilling program/graphic ratio/forming CNC program, which may cause problems such as easy placement deviation and poor coordination of structural parts. Since such problems are difficult to detect and can only rely on the supplier’s good process control, special attention needs to be paid when selecting suppliers.

To address PCB dimensional issues, the following measures can be taken:
(1) Design Verification: Thoroughly reviewing the PCB design and conducting design rule checks (DRC) and design for manufacturing (DFM) analysis to ensure proper dimensions, tolerances, and component footprints.
(2) Manufacturing Process Control: Implementing strict process controls during PCB fabrication, such as accurate temperature and pressure control during lamination, precise etching and drilling processes, and careful handling, can help minimize dimensional variations.
(3) Inspection and Testing: Conducting visual inspections, dimensional measurements, and verification checks throughout the manufacturing process to identify and rectify any dimensional issues before further assembly or testing.

✅ Galvanic Corrosion

Gold (Au) is a noble metal with excellent corrosion resistance, while copper (Cu) is a more active metal that can undergo galvanic corrosion when in contact with gold. Let’s assume that gold is the cathode, and copper is the anode.

Anode (Copper):
Copper (Cu) acts as the anode in the galvanic cell. It undergoes oxidation, losing electrons and forming copper ions (Cu2+). This oxidation reaction can be represented as follows:
Cu → Cu2+ + 2e-

Cathode (Gold):
Gold (Au) acts as the cathode in the galvanic cell. It undergoes reduction, gaining electrons from the anode and the external circuit. However, gold is a noble metal and does not readily undergo reduction reactions or form corrosion products.

Valency Changes:
In galvanic corrosion, the valency of the anode metal increases as it loses electrons and forms ions. In this case, copper (Cu) loses two electrons to form copper ions (Cu2+). The valency of copper changes from 0 to +2.

quality issue - galvanic corrosion - elepcb

Galvanic corrosion appears in the OSP process of selective gold plates. Due to the potential difference between gold and copper, the copper pad connected to the large gold surface during the OSP processing process will continue to lose electrons and dissolve into divalent copper ions, causing the pad to become smaller and affecting subsequent component placement and reliability.

Although this problem does not occur often, once it occurs, it is a mass problem. PCB Board manufacturers experienced in mobile phone PCB production will use computer software to screen out this part of the pads, pre-compensate during design, and set special rework conditions and limit the number of reworks in the OSP process to avoid problems. Therefore, this issue can be confirmed in advance when auditing the board factory.

✅ An Introduction to ELEPCB Factory

ELE PCB factory focuses on high-precision and difficult HDMI and multi-layer PCB board production, with a monthly production capacity of up to 25,000 square meters.

With 7 high-speed SMT lines and 2 THT lines, equipped with advanced equipment such as 3DSPI, X-RAY, and multi-temperature zone reflow soldering, we are able to ensure the production of high-precision products.

elepcb factory and smt machine
Production Line 003

The factory production lines have anti-static measures, and more than 95% of our production lines are skilled workers, who have extensive experience in assembling electrical components. The production equipment includes electric pneumatic tools, short circuit equipment, multimeters, ammeters, torque testing equipment, electric bridges, etc., all to ensure the smooth progress of production.

Our production line meets 5S requirements and can complete one-stop services of PCB design, PCB Fabrication, PCB assembly and box build assembly. We can arrange special line production and have a strict quality management system. Each production line has experienced employees and dedicated line follow-up personnel to ensure error-free production.

ELEPCB factory - smt and tht production line - pcb assembly machine

The factory will confirm the EQ with the customer before production, and only start production after confirmation. Our corporate culture emphasizes quality first, and we have almost never had major problems with quality.

These are the basis for us to ensure high-efficiency production and timely delivery. We have strength and we provide commitment and guarantee to our customers.

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About the Author
Jeffrey Lee
I'm Jeffrey, an experienced electronics engineer. As a seasoned content creator, I bring a deep passion for PCB-related topics, allowing me to communicate complex concepts with clarity and precision, making them accessible to a wide audience.
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