Microwave Tech - HDI Technology High Density Circuit Board: What is the process of making plug holes?

High density circuit board HDI expects to increase the density of the link, because this is considered appropriate and uses the small blind hole structure preset, specially designated products will use RCC material or hole-on-hole structure to make build-up lines as deemed appropriate.

If the thin film does not have enough glue to fill the hole, you must use other filling glue to fill the hole. This procedure is the plugging process.

Many technical problems will be encountered in the plugging process, which will continue to affect the quality of production. Then, how do you try to mitigate these problems? Which process technology should I choose?

Let's talk about it in detail below. The filling process must be smooth and solid, otherwise it is easy to cause the subsequent quality to be affected due to excessive sparseness or unfairness. After filling the through holes with glue, be sure to perform procedures such as brushing, de-smearing, chemical copper, electroplating, and circuit manufacturing to complete the inner circuit, and then the outer structure is manufactured.

In order to increase the density of the links, some carrier boards will use the hole-on-hole structure as deemed appropriate. Because of the ordinary filling procedures, there may be residual bubbles, because the residual quantity of the bubbles will directly affect the quality of the link. There is no clear standard for the number of bubbles allowed to remain. As long as the trust is not a problem, most of them will not become fatal.

But if the bubbles just fall in the orifice area, the chances of revealing the problem will increase relatively. If there are bubbles left in the orifice, the life force bubbles will sink down after brushing, and deep holes will be left after electroplating. It is easy to produce uncleanness during laser processing, because of this problem of poor conduction.

Therefore, the glue filling technology is a very important technology for the high density structure loading plate, especially the hole-up hole structure. The discussion on solving the hole filling technology can simplify the topic into two main directions.

One is the congenital existence of air bubbles that has not been eliminated. This is a problem arising from printing. The second is the problem that the bubbles inside have been discharged, and the subsequent volatilization regenerates.

For the former, the better disposal method is to take defoaming treatment after filling the glue and before baking, and try to remove the air bubbles inside to prevent leaving behind. The ink can be defoamed first after the ink is mixed, and then it is considered appropriate in the filling and supplemented by a method that is less likely to produce foam.

Some manufacturers have introduced so-called closed squeegee presets, and there are also specially designated manufacturers that preset extrusion facilities or vacuum printers. These can be tried.

For the latter, it should be avoided to sprout the vitality bubble after deaeration, this part involves the use of supplementary materials. In order to manipulate the special properties and final physical and chemical properties of the ink, different dosages of supplements and thinners are used to adjust the special properties of the ink. But this approach will be tested in the hole-filled ink meeting.

Most thinners are volatile. When filling holes and baking volatiles, the liquid turns into gas, and more bubbles will sprout in a short period of time. But ordinary ink drying standard styles dry from the outside first, and then harden layer by layer inward, because this air bubble will be left in the inside and cannot be discharged and become empty.

This kind of problem can be dealt with by the ultraviolet curing method, filling the holes with photosensitive ink and curing by low-temperature photosensitive first, and then using thermal curing to complete the follow-up response. Because volatile matter has no way to make bubbles grow in the hardened natural resin, it is not easy to cause the appearance of bubbles.

Another method of most manufacturers is to try their best to use volatile-free inks, and at the same time reduce the baking start temperature to remove the volatiles, and then when the hardness reaches a certain level, then start the full-hardening baking. .

These two methods have their own advantages and disadvantages, but in terms of the amount of residual bubbles, whether the former or the latter should try to use low-volatile ink is more helpful.

What is the plugging process? After the ink is hardened, it can be brushed in all aspects. In order to fill the holes, the ink will be slightly higher than the surface of the hole and then be brushed and smoothed. In order to reduce the difficulty of brushing after full hardening, some manufacturers think it is appropriate to use two-stage bake. After the ink is hardened one-half of the hardening, the second stage bake is applied and then the second stage bake is applied. These are all suitable. Technical information about plug holes.

Extended reading: HDI

For the electrical requirements of high-speed signals, the circuit board must provide impedance control with the special properties of alternating current, experience in high-frequency transmission, and reduce indispensable radiation (EMI). If the structure of Stripline and Microstrip is used as deemed appropriate, multi-layering becomes an indispensable preset.

In order to reduce the quality of signal transmission, insulating materials with low dielectric coefficient and low attenuation will be considered appropriate. In order to reduce the size and array of suitable electronic components, the density of circuit boards is also increasing. In response to needs.

BGA (Ball Grid Array), CSP (Chip Scale Package), DCA (Direct Chip Attachment) and other component assembly forms are exposed, which has promoted the advancement of printed circuit boards to an unprecedented level of high density.

Any hole with a diameter of less than 150um is called a microvia in the industry. The circuit made by the geometric structure technology of this microvia can increase the benefits of assembly, space utilization, etc., and at the same time contribute to the miniaturization of electronic products. It also has its indispensability.

For circuit board products of this type of structure, there have been many different names in the industry before to call such a circuit board.

For example, European and American companies used the sequential structure because the manufacturing procedures were deemed appropriate, because this type of product is called SBU (Sequence Build Up Process), which is generally translated as "Sequence Build Up Process".

As for the Toyo company, the hole structure produced by this type of product is much smaller than that of the previous hole, because the manufacturing technology of this type of product is called MVP (Micro Via Process), which is generally translated as "Micro Via Process".

Some people are also called MLB (Multilayer Board) because of the traditional multi-layer board, because this person calls this type of circuit board BUM (Build Up Multilayer Board), which is generally translated as "build-up multi-layer board".

The IPC Circuit Board Association of the United States proposed to call this type of product the generic name of HDI (High Density Intrerconnection Technology) in order to prevent confusion. If it is directly translated, it becomes a high density connection technology.

However, there is no way to reflect the characteristics of the circuit board, because most of the circuit board manufacturers call this type of product HDI board or the full Chinese name "High Density Interconnection Technology".

However, due to the problem of the smoothness of spoken language, some people directly call this type of product "high density circuit board" or HDI board.