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  • Some knowledge of via hole
    Date :2017-3-3


    With the electronic products to the "light, thin, short, small" direction, PCB to high density, difficult development, so a large number of SMT, BGA PCB, and customers in the placement of components required holes, A role:
    1. To prevent PCB over-wave soldering tin from the through-hole through the element surface caused by short-circuit; In particular, we put the vias on the BGA pad, you must first do plug hole, and then gold-plated, easy BGA welding.
    2. Avoid flux remaining in the vias;
    3. Electronic factory surface mount and component assembly after the completion of the PCB in the test machine to take the vacuum to form a negative pressure to complete:
    4. To prevent surface solder paste into the hole caused by Weld, affecting the placement;
    5. To prevent wave soldering when the tin beads pop, resulting in short circuit.


    Realization of Conducting via hole
    For the surface mount plate, especially the BGA and IC placement on the through hole plug requirements must be flat, convex and concave positive and negative 1mil, no holes on the edge of the red on the red; conductive hole tin beads, in order to achieve the customer's Requirements, through the hole plug hole process can be described as varied, especially the process is very long, difficult to control the process, often in the hot air leveling and green oil resistance to solder test oil; curing after the explosion and other problems occur. Is based on the actual conditions of production, a variety of plug-in PCB process summarized in the process and the advantages and disadvantages of some comparison and elaboration:
    Note: The principle of hot air leveling is the use of hot air will be printed on the circuit board and the hole to remove excess solder, the remaining solder evenly covered in the pad and unblocked solder lines and surface packaging point, is printed circuit board surface treatment one.


    The via hole process after HAL
    The process flow is: plate resistance welding → HAL → plug hole → curing. The use of non-Cypriot process for the production, hot air leveling with aluminum plate or block ink ink network to complete the requirements of all the requirements of the hole through the hole hole. Plug hole ink can be used photosensitive ink or thermosetting ink, in ensuring the same wet film color, plug hole ink is best to use the same ink with the board. This process can ensure that the hot air after leveling through the hole can not afford to lose oil, but easy to cause plug hole ink pollution board, not flat. Customers in the placement of easy to cause Weld (especially BGA). Many of the customers do not accept this method.

    The via hole process before HAL
    1. With aluminum plug hole, curing, grinding plate after the graphics transfer
    The process of drilling with CNC drilling, drilling holes to be made of aluminum, manufacturing screen, the plug hole, to ensure that the hole through the hole full hole, plug hole ink plug hole ink can also be used thermosetting ink, its characteristics must be large hardness , Resin shrinkage change is small, and hole wall adhesion is good. Process: pre-treatment → plug hole → grinding plate → graphics transfer → etching → plate resistance welding
    With this method can ensure that the hole through the hole straight, hot air leveling will not have oil, but the process requires a one-time thickening of copper, so that the hole wall copper to meet customer standards, so the whole board copper requirements High, and the performance of the grinding machine also has a high demand to ensure that copper panels, such as resin completely removed, copper surface clean, not contaminated. Many PCB plants do not have a one-time thickening of copper technology, as well as the performance of the equipment does not require, resulting in this process in the PCB factory use much.
    2. With aluminum sheet plug hole after the direct silk screen plate resistance welding
    This process with CNC drilling, made of screen, installed in the screen printing machine on the hole, after the completion of the hole after the parked no more than 30 minutes, with 36T wire mesh direct printing plate surface welding, the process: pre-treatment - plug Hole - silk screen - pre-bake - exposure to a development - curing
    With this process to ensure that the through-hole cover oil is good, plug hole formation, wet film color consistent, hot air leveling to ensure that the vias are not on the tin, the hole is not hidden tin beads, but easy to cause the hole after curing ink Solder, the shape of poor solderability; hot air leveling the edge of the hole after the bubble out of oil, the use of this method of production control more difficult to be technical engineers to use special processes and parameters to ensure that the plug hole quality.
    3. Aluminum sheet hole, development, pre-curing, grinding plate after the plate resistance welding
    With CNC drilling machine, drill out of the requirements of the hole of the aluminum, made of screen, installed in the transfer screen printing machine on the hole, plug hole must be full, both sides of the better, and then through the curing, grinding plate plate processing process For: pre-treatment - plug a pre-bake - development - pre-curing - plate resistance welding
    As this process using plug hole curing can ensure that the HAL after the hole can not get off the oil, oil, but after the HAL hole through the tin beads and on the hole on the tin is difficult to completely solve, so many customers do not receive.


    Board resistance welding and hole at the same time to complete
    This method uses 36T (43T) wire mesh, installed in the screen printing machine, the use of pad or nail bed, in the completion of the board at the same time, all the vias plug, the process is: pre-treatment - silk screen - Preblowing - exposure - developing - curing
    The process flow time is short, the utilization of the protection is high, can ensure that the hot air after leveling the hole can not afford the oil, the hole is not on the tin, but because of the use of silk screen plug hole, in the hole with a lot of air, When the air expansion, erosion resistance solder film, resulting in empty, uneven, hot air leveling there will be a small amount of conduction hole tin. At present, my company after a lot of experiments, choose different models of ink and viscosity, adjust the pressure of silk screen, etc., basically solved the hole and not flat, has been used in this batch production process.



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