How to use a miniature PCB coil as an inductive sensor component?
How to use a miniature PCB coil as an inductive sensor component?
When designing the PCB, we need to consider several issues: 1. Single-layer or double-layer board? 2. All through-hole or through-hole plus surface mount? 3. Does the factory support glue bonding?
In practical terms, these are the mainstream design and manufacturing solutions: Solution 1: All through-hole, single-sided board. Cost analysis: Manual insertion, one wave soldering pass. Early power supplies were designed this way, as wave soldering and reflow soldering were not yet widespread; they used the most traditional solder pots.
All through-hole + single-sided paper PCB is almost a hallmark of that era and is rarely used now. Solution 2: Surface mount + through-hole, surface mount and through-hole on the same side. Cost analysis: One reflow soldering pass, then one wave soldering pass. One reflow soldering machine + one wave soldering machine is actually standard equipment on many companies' production lines, so this type of power supply design is the easiest to manufacture.
Option 3: Surface Mount + Through-Hole Components (SMT + Through-Hole). SMT components are on the bottom, through-hole components on the top. Cost Analysis: First, reflow soldering is performed to solder the SMT components; then a fixture is made to shield the SMT components; finally, the through-hole components are placed and wave soldered. The cost of this option is: wave soldering + reflow soldering + fixture cost. The image shows the fixture, which uses a special baffle to block the SMT components, exposing only the through-hole components' leads for wave soldering.
However, this requires a sufficient distance between the SMT components and the through-hole components, and the fixture itself is not inexpensive. In reality, due to the compact size requirements of modern power supplies, it's impossible to provide sufficient space for fixture isolation between the SMT and through-hole component leads. A common practice is to use glue to first attach the SMT components to the back of the circuit board, then place the through-hole components, and finally wave solder them all together.
The cost of this option is: glue cost + wave soldering cost. The reason for this approach is its cost-effectiveness, provided your factory has a red glue machine. Option 3 is also the most commonly used production method in modern power supply manufacturing. Of course, if your company doesn't have a red glue machine, then you'll have to choose Option 2, which involves both reflow and wave soldering. Compared to Option 3, Option 2 takes up significantly more PCB area because both surface mount and through-hole components are on the same mounting surface, indirectly increasing the demands on the power supply engineer's PCB layout skills.
PS: Option 3 also has an even more cost-effective method: manufacturing a single-sided board, keeping everything else the same. The advantage is that it saves on the PCB unit price; the disadvantage is that routing becomes more difficult. As you may have noticed, this board requires flying leads. Flying leads are actually custom-made parts and are inconvenient to connect by machine, so it's recommended to use a double-sided board, as the cost of double-sided boards isn't very high now.
Option 4: Two-sided surface mount + through-hole Option 4 is definitely a high-end option; those who don't care about cost can consider this approach. Cost Analysis: The main cost of Option 4 is the additional reflow soldering step compared to Option 3 or Option 2. Option 5: Two-sided Surface Mount (SMT) Solution Cost Analysis: Two reflow soldering steps + the increased cost of SMT components. This option is rarely used, for a simple reason: as mentioned before, space is extremely limited in switching power supplies. SMT capacitors occupy a much larger area than through-hole capacitors and are harder to source.
Throughout the through-hole pins, the connection between upper and lower layers cannot be achieved, resulting in numerous additional vias. Of course, this solution also has its advantages, namely high product reliability, as full SMT production offers the potential to completely eliminate manual labor. These are the five most commonly used solutions in modern power supplies. Options 1, 2, and 3 are all very common design solutions nowadays. The specific decision depends on coordination between you and the factory. The base of SMT capacitors takes up a significant amount of space.
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