Mar13
What is CTE (Coefficient of Thermal Expansion)? What is α2-CTE? How Does CTE Affect PCB Quality?

CTE for Train Tracks

CTE (Coefficient of Thermal Expansion) refers to how a material’s geometric properties change as its temperature rises or falls due to thermal expansion and contraction. In practical applications, CTE is divided into two main categories:

  • Coefficient of Linear Thermal Expansion – Applies to solids
  • Coefficient of Volume Thermal Expansion – Applies to gases

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Mar06
What is the Popcorn Effect in PCBs and Electronic Components?

The Popcorn Effect in PCB and electronic components refers to the delamination (board cracking) or formation of bubbles when exposed to high temperatures during soldering. This phenomenon is similar to how popcorn pops—it happens because of trapped moisture inside. When heated, the internal moisture turns into steam, and as the temperature increases, the pressure from the steam rises. If this pressure exceeds the bonding strength of the component, PCB, or IC package, it causes a sudden expansion—just like a kernel turning into fluffy popcorn.

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Feb27
What Is Solder Mask (S/M)? What Is Its Purpose on a PCB? Why Is It Usually Green?

What Is Solder Mask (S/M)? What Is Its Purpose on a PCB? Why Is It Usually Green?

In discussions about printed circuit boards (PCBs), you’ll often hear the term Solder Mask (S/M). But what exactly is a solder mask, and what role does it play in a PCB? Some also refer to it as solder resist.

What Is a Solder Mask?

As the name suggests, a solder mask is used to prevent solder from accidentally adhering to areas that shouldn’t be soldered during assembly. The color you see on a PCB is actually the printed solder mask layer, not the natural color of the PCB material.

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Feb20
PCB Popcorn Effect: Why it Happens and How to Stop It

The Relationship Diagram Between Temperature and Vapor Pressure

The main reasons for PCB delamination or “popcorning” are primarily (1) moisture absorption and (2) excessive α2/Z-axis CTE (Coefficient of Thermal Expansion). Among these, moisture absorption is responsible for about 70% of delamination issues. Other factors, such as uneven thermal expansion, inconsistent cooling and heating, mechanical damage during processing, or poor oxidation treatment, can also contribute—but their impact is generally much lower.

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Feb06
Causes of Solder Empty and Tombstoning in Small Chip of Resistors and Capacitors

small chip tombstoneRecently, some people have asked about issues with solder empty in small chip SMD components like resistors and capacitors. Even after thoroughly checking the reflow oven profile settings and confirming everything is correct, solder empty still frequently occur with these components, often in fixed positions. Observations of the solder also don’t show any signs of non-wetting or de-wetting, leaving many puzzled.

In reality, the cause of solder empty in these components isn’t that hard to understand! It’s essentially the same reason tombstoning occurs. To put it simply, it all comes down to this: “The solder paste on the two terminal ends of the component melts at different times, resulting in uneven forces and causing one side to lift.”

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