Via Requirements
In order to promote the development of PCB, higher requirements are also put forward for the printed board manufacturing process and surface mount technology. The Via hole plugging process came into being.
There is only enough copper in the via hole, and the solder mask can be plugged or not;
There must be tin-lead in the via hole, and there is a certain thickness requirement (4 microns), and there must be no solder resist ink entering the hole, causing tin beads to be hidden in the hole.
The via holes must have solder resist ink plug holes, are opaque, and must not have tin rings, tin beads, and flatness.
With the development of electronic products in the direction of small size, circuit boards are also developing in high density and high difficulty.
Plugging holes when mounting components has the following functions:
Prevent short circuit caused by tin penetrating through the component surface from the via hole when the PCB is over wave soldering.
Prevent flux from remaining in vias.
Prevent the solder paste on the surface from flowing into the hole to cause false soldering and affect the placement.
Prevent tin balls from popping out during wave soldering, causing short circuits.
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Realization of Conductive Hole Plug Technology
For surface mount boards, especially for BGA and IC mounting, the via hole plug hole must be flat, with a bump of plus or minus 1mil.
In order to do better, there are many kinds of via hole plugging processes, the process flow is very long, and the process control is difficult.
There are often problems such as oil loss during hot air leveling and green oil solder resistance tests, and oil explosion after curing.
According to the actual production conditions, answer the circuit board plugging process.
The working principle of hot air leveling is to use hot air to remove excess solder on the surface of the printed circuit board and in the holes.
The remaining solder evenly covers the pads, non-resisting solder lines and surface packaging points, which is one of the surface treatment methods of printed circuit boards.
Plug Hole Process after Hot Air Leveling
Board solder mask → HAL → plug hole → curing
The non-plug hole process is used for production, and the aluminum sheet screen or ink blocking screen is used to complete the plug holes of all the fortresses after hot air leveling.
The plugging ink can be photosensitive ink or thermosetting ink. In the case of ensuring the same color of the wet film, it is better to use the same ink as the board surface for the plugging ink.
This process can ensure that the via hole does not drop oil after hot air leveling, but it is easy to cause plugging ink to contaminate the board surface and make it uneven. Customers are prone to cause virtual soldering (BGA) during placement. Our company does not recommend this method.
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Hot Air Leveling Front Plug Hole Process
Graphic Transfer with Aluminum Sheet
Pre-processing → Plug hole → Grinding plate → Pattern transfer → Etching → Solder mask on board surface
The process uses a CNC drilling machine to drill out the aluminum sheet that needs to be plugged, and makes a screen to make a plug hole to ensure that the plug hole of the via hole is full. The plug hole ink can also be thermosetting ink, which must be hard and resin The shrinkage change is small, and the bonding force with the hole wall is good.
This method can ensure that the plug hole of the via hole is flat, and the hot air leveling will not cause quality problems such as oil explosion and oil drop at the edge of the hole.
However, this process requires one-time thickening of copper to make the copper thickness of the hole wall meet the customer’s standard. Therefore, the requirements for copper plating on the entire board are very high, and the performance of the grinding machine is also very high. Ensure that the resin on the copper surface After it is completely removed, the copper surface is clean and not polluted.
Many PCB factories do not have a one-time copper thickening process, and the performance of the equipment does not meet the requirements, resulting in that this process is not used much in PCB factories. Wonderful PCB can meet your needs, we have a brand new factory.
Solder Resistance on the Screen Printing Board Surface after Plugging the Aluminum Sheet
Pre-treatment – plug hole – silk screen – pre-baking – exposure-development – curing
In this process, a CNC drilling machine is used to drill out the aluminum sheet that needs to be plugged to make a screen, which is installed on the screen printing machine for plugging. After the plugging is completed, it should not be parked for more than 30 minutes, and the 36T screen is used to directly screen the solder on the surface of the board.
It can ensure that the oil on the via hole cover is good, the plug hole is flat, and the color of the wet film is consistent. After hot air leveling, it can ensure that the via hole is not tinned and there is no tin ball hidden in the hole, but it is easy to cause the ink in the hole to be on the pad after curing.
After the hot air is leveled, the edge of the via hole will foam and lose oil. It is difficult to control the production by using this process method. Process engineers must use special processes and parameters to ensure the quality of the plug hole.
Aluminum Sheet for Board Surface Solder Mask
Pretreatment – plug hole – pre-baking – development – pre-curing – board surface solder mask
Use a CNC drilling machine to drill out the aluminum sheet that requires the plug hole to make a screen, install it on the shift screen printing machine to plug the hole, the plug hole must be full, and it is better to protrude on both sides, and then after curing, the plate is ground for surface treatment.
Since this process adopts plug hole curing, it can ensure that the via holes after HAL will not drop oil or burst oil, but after HAL, it is difficult to completely solve the hidden tin beads in the via holes and the tin on the via holes. So this method is not recommended.
Solder Masking and Plugging of the Board Are Completed at the Same Time
Pretreatment — Silkscreen — Prebaking — Exposure — Development — Curing
This method uses a 36T (43T) screen, installed on the screen printing machine, using a backing board or a bed of nails, and plugging all the via holes while completing the board.
This process takes a short time, and the utilization rate of the equipment is high, which can ensure that the via holes will not drop oil and the via holes will not be tinned after hot air leveling.
However, due to the use of silk screen printing to plug holes, there is a large amount of air in the via holes. When curing, the air expands and breaks through the solder mask, resulting in voids and unevenness.
Wonderful PCB has gone through a lot of experiments, choosing different types of inks and viscosities, adjusting the pressure of silk screen, etc., basically solving the holes and unevenness of vias, and has adopted this process for mass production.
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About Wonderful
Shenzhen Wonderful Technology Co., Ltd. is China’s top model and small batch circuit board manufacturer.
The company targets precision circuit board samples and small batches as the main target market. Since its establishment, it has adhered to the development concept of good quality and important reputation.
Invest huge sums of money to introduce advanced equipment, strictly regulate the operating standards and QC standards for incoming and outgoing materials, to ensure that the shipped products reach Seiko quality.
The self-developed ERP management system can realize the whole process of paperless operations such as online ordering, online payment, online production progress query, online logistics tracking, and online statistical report production, which greatly improves work efficiency.
It ensures that each order can be shipped quickly. After more than ten years of development, the company’s products and services have been well received by the market.
As well as the opening of an electronic component mall, integrated circuits, semiconductors, resistors, capacitors and other products are sold.
The company’s scale is developing rapidly, and the sample and small batch shipment capacity reaches 500 models/day.
The products are widely used in communications, medical equipment, industrial control products, aviation, military products, testing instruments,Automotive, computers and other peripheral products.
We will continue to pay attention to customers, with efficient delivery speed and perfect after-sales service, to become the most trusted brand supplier in the PCB industry.
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