HDI blind hole design, did you notice this detail?

yvonneGan

HDI blind hole design, did you notice this detail? [Copy link]

Author: Wang Huidong, member of Mr. Expressway of Yibo Technology

Rao Xiaoxiao said: I love three things: the sun, the moon, and the circuit board.
A Mao said: I'll just take a look.
A Mao, who had just arrived at the workshop, saw from afar the beautiful face of PMC's beauty Rao Xiaoxiao. Her beautiful eyebrows were slightly frowned, and her delicate face was reflected with a slight worry. There was a more pitiful heartbeat, and more of the kind of focused and calm beauty.
People sighed at this moment: the world is noisy and flashy, and a lifetime is gone in a flash. Beauty is like a dream, and a lifetime of beauty is dim.
A Mao quietly walked behind Xiao Xiao and saw that she was staring at the PCB in front of the monitor, the enlarged PCB board.
A Mao felt that this PCB was a little familiar, and took another look. Oh! Isn't this the HDI board that he reinvested and processed outside? Yes, it is the board that will be online soon.
I saw a picture displayed on the screen, and the surface of the pad was bumpy.
A Mao asked Xiao Xiao softly, why did this batch of pads become like this.

Xiaoxiao said: Amao, you should ask your PCB processing factory, the dimple on this batch of blind holes is obviously beyond the standard, compared with the last time, one is sky and the other is underground.

(, downloads: 0)

Archive of pictures from the previous batch

(, downloads: 0)

What is HDI

HDI (High Density Interconnection) is the abbreviation of high-density interconnect PCB. It is an abbreviation of multi-layer buried/blind hole PCB produced on the basis of traditional multi-layer circuit board manufacturing technology, through high-density fine wiring and tiny via technology, supplemented by laser drilling, horizontal/vertical PTH wet process and other processes.

According to the definition in IPC-2226:
blind or buried via diameter ≤ 0.15mm [0.00591 in], pad diameter ≤ 0.35mm [0.0138 in], through laser or mechanical drilling, dry/wet etching, pattern transfer, and electroplating to form a conductive coating.
Note: For hole diameters > 0.15mm [0.00591 in], refer to the vias in this standard.

Common drilling size range for HDI:
3-5mil, generally the middle value of 4mil is taken for design and production.

Commonly used IPC standards for HDI
1) IPC/JPCA-2315-Guidelines for high-density interconnection structure and microvia design
2) IPC-2226-Part of the high-density interconnection (HDI) printed circuit board design guidelines
3) IPC/JPCA-4104-Dielectric material verification and performance specification for high-density interconnection (HDI) structure
4) IPC-6016, Verification and performance specification for high-density interconnection (HDI) structure
(, downloads: 0)

The processing principle of HDI blind holes:
non-mechanical drilling, blind holes with a hole diameter of less than 0.15mm (6mil), and blind hole bottom pads of less than 0.25mm (10mil) are specifically called Microvia micro-vias or microvias.
Microvias are usually processed by laser, and the light types mainly include infrared light and ultraviolet light.
(, downloads: 0)

There are usually two common LASER excitation methods:
one is UV light, and the other is sealed CO2 gas

Utilizing the thermal energy of infrared rays, when the temperature rises or the energy increases to a certain level, such as the melting point, ignition point or boiling point of organic matter, the interaction force or binding force of the organic molecules will be greatly reduced to the point where the organic molecules will separate from each other and become free or dissociated. Due to the continuous energy provided by the laser, the organic molecules will escape or burn with the oxygen in the air to become carbon dioxide or water gas and disperse. Since the laser is processed with an infrared beam of a certain diameter, tiny holes are formed.

(, downloads: 0)

Solid-state Nd: YAG ultraviolet laser emits a high-energy ultraviolet light beam, which uses its optical energy (high-energy photons) to destroy the molecular bonds of organic matter (such as covalent bonds), metal crystals (such as metallic bonds), etc., forming suspended particles or atomic clusters, molecular clusters or atoms, molecules that escape and finally form blind holes.

(, downloads: 0)

Laser hole filling method:

(, downloads: 0)

Advantages of electroplating via filling:
1. It is conducive to the design of stacked vias and via on pads
2. It improves electrical performance and helps high-frequency design
3. It helps to dissipate heat and increase current
4. Via filling and electrical interconnection are completed in one step
5. The blind hole is filled with electroplated copper, which has higher reliability

Since the aperture of the laser hole is relatively small, at 0.075-0.2mm, electroplating is used to increase the copper thickness in the hole, thereby achieving the purpose of plugging the hole.

(, downloads: 0)

The maximum thickness-to-diameter ratio of the plate for via-filling electroplating is 1:1, usually 0.8:1, that is, with a 4-mil laser hole, the maximum depth of the via-filling is 4 mil, and the normal depth is about 3.2 mil. The following figure is a typical HDI board stackup diagram, and it can be seen that the dielectric thickness of all blind via layers does not exceed the 1:1 thickness-to-diameter ratio.

(, downloads: 0)

The influence of blind hole depression on welding:
Due to the blind hole diameter or through hole thickness-diameter ratio electroplating filling (hole structure), as well as the basic principle limitation of electroplating additives, the Dimple value is inevitable. Since blind holes involve subsequent welding processes, there are usually different specifications for the Dimple value, generally requiring Dimple ≤ 15um.

The first batch of dimple meets the production requirements.

(, downloads: 0)

The second batch of dimple clearly exceeded the standard.

(, downloads: 0)

If the dimlpe on the blind via pad exceeds the standard, as shown in the figure below, a void will be generated when the BGA solder ball is soldered.

(, downloads: 0)

The figure below shows that the depression on the pad of the hole in the plate and the blind hole is relatively large, which is easy to produce voids and bubbles during welding.

(, downloads: 0)

If the pad is not in the middle of the solder joint, it will cause cracks on one side of the solder joint, and the defect will occur, especially after aging and vibration testing, this defect will be more prominent.

(, downloads: 0)

After listening to Xiao Xiao's analysis, A Mao opened his mouth in shock. This, this, this... Beauty is not scary, what is scary is that beautiful women are educated, and they are very professional.
A Mao was stunned for a long time, and then asked: "Xiao Xiao, what do you think I should do with this concavity when I make HDI boards in the future?"
Xiao Xiao said domineeringly:
1. When designing, the thickness-to-diameter ratio of the blind hole should not exceed the standard, and it should be controlled at about 0.8:1.
2. The laser blind hole is treated with special VCP hole-filling electroplating, and the concavity is controlled below 15um.
3. We will find a way to solve this batch, because you are our God.

In the end, the PCBA factory took it all.

The question is,
when designing laser blind holes, have you considered the problem of the blind hole thickness-to-diameter ratio? Have you paid attention to the abnormality of the concavity exceeding the standard during hole-filling electroplating? Have the PCBA factory put forward suggestions for improvement? Come on, once Wusu opens, the more you talk, the more excited you are...

qwqwqw2088

I asked JLC to make blind and buried vias a few years ago. The drawings were sent to me, but they were returned. They couldn't make it.

I don't know how they are now.

HDI blind hole design, did you notice this detail? [Copy link]

Latest reply