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The selection and evaluation of magnetic separators for wireless charging receivers usually revolve around magnetic permeability, saturation magnetization, and losses. These three sets of data answer the question of 'what materials can do in an ideal state'. But a piece of 0.08 mm thick broken magnetic nanocrystal magnetic isolation sheet, after being removed from the reel, visually aligned, pressed onto the back of the coil, and then peeled off the release film, undergoes several mechanical stresses throughout the entire process. The specification sheet will not tell the engineer how easily this material is "damaged" on the production line.
The issue of assembly yield rarely occurs in the form of "material failure". It usually manifests as: the efficiency of some units is several percentage points lower than the sample, the FOD false triggering rate increases in specific batches, and the temperature rise is higher in local areas. These phenomena are difficult to attribute in the overall testing, as the appearance of the magnetic separator is intact and the magnetic properties of the incoming materials are also qualified - the changes occur at the fragment level and are not included in the testing items of the specification sheet.
The 'second fragility' of fragmented magnetic structures: fragments are fixed by adhesive layers, not by metallurgical bonding
The flexibility and low eddy current losses of nanocrystalline magnetic separators come from magnetic fragmentation: the continuous nanocrystalline strip is divided into small, mutually insulating fragments, and the gaps between the fragments cut off the eddy current path. But this structure also means that the continuity of the magnetic circuit of the magnetic separator does not depend on the metallurgical bonding between the fragments, but on the adhesive backing and cover film holding the fragments in relative positions.
This fixing method is effective under flat, static, and stress free conditions. However, during the installation process, three types of stresses will simultaneously act on the fragment layer:
Peel stress
When the release film is peeled off from the backing adhesive, the peeling force will be transmitted to the fragment layer through the adhesive layer. If the peeling force of the release film is too high or the peeling angle is inconsistent, the fragments may be "lifted up" locally, causing slight displacement with adjacent fragments. Displacement does not change the appearance, but changes the width of the fragment gap, and the equivalent magnetic resistance changes accordingly.
Compression stress
When the magnetic separator is pressed onto the back of the coil, uneven pressure distribution can cause the fragment layer to experience local shear. The magnetic separator after magnetic fragmentation is a stack of "glue fragment glue" in the thickness direction, and shear stress is concentrated at the edge of the fragments, which may cause local debonding.
Grasping and alignment stress
When using suction nozzles or clamps to pick up and place magnetic separators in automated equipment, thin sheets may bend during vacuum suction and release processes. The bending stiffness of the 0.08 mm magnetic separator is very low, and the local negative pressure of the suction nozzle may cause uncontrollable deformation of the sheet during picking and placing.
When these three types of stress appear separately, they may not necessarily be fatal, but when they are superimposed on the same production line, the probability of fragment misalignment and local debonding increases with thickness reduction. The thinner the thickness, the weaker the mechanical constraint of the fragment layer, and the more significant the impact of mounting stress on the magnetic circuit.
Feeding form: Differences in adaptability between roll and sheet production lines
The feeding form of the magnetic separator is a pre variable of the mounting yield.
Roll material supply
Suitable for automated continuous mounting, the magnetic separators are arranged at fixed intervals on the release film, and the equipment completes material retrieval through a peeling knife and a suction nozzle. The advantage is fast pace and stable alignment benchmark, but the yield is highly dependent on the consistency of the release film peeling force. If the peeling force fluctuates in the direction of the roll length, some fragments in certain sections may be disturbed during peeling. The coil also requires the magnetic separator to withstand a certain degree of bending in the wound state. For ultra-thin sheets of 0.05-0.08 mm, the winding radius and tension need to match the bending stiffness of the material, otherwise the fragmented layer will already be subjected to prestress inside the coil.
Sheet feeding
Suitable for small batch or irregular mounting, the magnetic separator is placed in a single piece form on a tray or carrier tape. The sheet avoids pre stress during winding, but increases the difficulty of single piece grasping: the flatness of thin sheets in the tray, the reliability of adsorption and release, and the consistency of manual or semi-automatic picking and placing operations all affect the integrity of the fragment layer. The installation yield of sheet feeding depends more on operational standards rather than equipment accuracy.
When selecting, it is not enough to just ask "whether there is a roll", but to confirm the matching relationship between the peeling force range of the roll, the winding radius and the material thickness, as well as the flatness of the sheet and the type of release film. The combination of feeding form, production line rhythm, mounting accuracy, and material thickness determines the starting point of mounting yield.
Back adhesive modulus: The low modulus adhesive layer absorbs stress, but may also "release" fragments
Adhesive plays a dual role in the structure of magnetic separators: it fixes fragments and also transmits mounting stress. These two roles have different requirements for the modulus of the adhesive layer.
The high modulus adhesive layer provides a more secure fixation for fragments, making them less prone to displacement during peeling and pressing. But high modulus means that the adhesive layer is not easily deformed under stress, and shear stress will be transmitted more to the edge of the fragments, increasing the risk of local debonding. The low modulus adhesive layer can absorb some of the mounting stress and reduce the stress concentration at the edge of the fragments. However, after long-term high temperature or repeated bending, the low modulus adhesive layer may undergo creep, and the relative position between the fragments gradually drifts.
For ultra-thin magnetic separators, a common compromise in engineering is to choose a glue layer with a glass transition temperature higher than the production line operating temperature but moderate modulus: to maintain sufficient fixing force at the mounting temperature and not concentrate stress on the edge of the fragments during peeling and pressing. When selecting, it is necessary to confirm the modulus or Tg data of the backing adhesive with the supplier, as well as the peeling force range of the adhesive layer at the target mounting temperature, rather than just confirming the "backing adhesive type".
Selection judgment based on "production line adaptability"
Firstly, consider the assembly yield as an independent verification item, rather than an accessory of incoming inspection
The incoming inspection measures the magnetic properties and appearance in a flat state, while the assembly yield measures the magnetic circuit integrity of the material under production line stress. When selecting, the grabbing, alignment, pressing, and release film peeling should be completed according to the actual production line conditions during the sample stage, and then the equivalent magnetic permeability or overall efficiency of the magnetic isolation sheet should be retested, rather than assuming that "if the incoming material is qualified, it will be the same as sticking it on".
Secondly, confirm the matching relationship between the feeding form and material thickness
For ultra-thin magnetic separators with a thickness of 0.05-0.08 mm, it is necessary to confirm the consistency of the winding radius, tension, and peeling force when feeding the coil material; Sheet feeding requires confirmation of flatness and reliability of adsorption and release. The feeding form is not a logistics issue, it directly affects the initial state of the fragment layer before installation.
Thirdly, inquire with the supplier about the peel strength and adhesive modulus of the release film, rather than just confirming the presence of adhesive
High peeling force or batch fluctuations can disturb the fragment layer during the peeling process; The mismatch of adhesive modulus will concentrate the mounting stress on the edge of the fragments. These two parameters usually do not appear in conventional specifications, but they have a significant impact on the installation yield of ultra-thin magnetic separators.
Fourthly, in ultra-thin decision-making, put "production line yield" and "magnetic properties" on the same table
The 0.08 mm magnetic separator has better magnetic performance and thickness than 0.11 mm, but if the production line yield decreases due to fragment misalignment, the efficiency loss and FOD consistency risk at the whole machine level may offset the benefits brought by thickness. The ultra-thin boundary is not only determined by saturation margin and temperature rise, but also by whether the production line can stably adhere the fragment layer "completely" to the target position.
Advanced Institute (Shenzhen) Technology Co., LtdThe wireless charging receiver magnetic isolation sheet product line covers ferrite composite sheets and nanocrystalline composite sheets, with a thickness of 0.03-0.3mm for the nanocrystalline series. It can provide two feeding forms, roll and sheet, release film peeling force range, and adhesive modulus data, and supports magnetic performance retesting after installation according to customer production line conditions during the sample stage.
The product is suitable for mobile phones and wearable receiver scenarios that require high assembly yield. For more technical information, please visithttps://www.avanzado.cn/products/gold-plated-conductive-cloth.html.