From the continuous update and development of computers, mobile phones and other electrical products, we can see the development of PCB manufacturing industry. HDI board making is the inevitable product of PCB development and a trend of PCB making. It is different from traditional PCB and has the following obvious characteristics:
1. Laser drilling is used to improve wiring density.
2. Lightness, thinness and shortness of PCB
1. LAY-UP structure
1. materials
1) RCC-Resin Coated Copper (Chinese called resin-coated copper foil or adhesive-backed copper foil)
A) Composition: Cu+Resin, the thickness of copper is 1/2 and 1/3 OZ, the thickness of resin layer is 55, 60, 65, every 5um, and the thickest is 100um.
B) Features: 100% resin content (easy for Laser drilling)
C) Dielectric constant: 3.2-3.8, generally calculated as 3.6.
D) Size: Generally speaking, RCC size is 1.2inch(MI larger than the previous cutting size of RCC material (no indication is required in MI).
2) Laser-specific P film: such as 106,1080. Its structure is different from ordinary P-sheet, and the glass cloth structure is loose to facilitate laser drilling.
Note: At present, ETON can only be made by RCC lamination, and P laser is still under test.
2. HDI board structure
1) traditional structure: such as 1+4+1(with IVH or without IVH)
2) Special structure: such as 2+4+2(with IVH or without IVH) (second-order blind hole design)
3) According to the structural requirements, the following overlapping holes and near holes should be specially checked.
(a) blind hole and buried hole (very important)
(b) Blind holes and through holes
(c) Buried holes and through holes
Among them, (a) is very important. The overlap of blind holes and buried holes may cause the functional influence of open circuit.
When the blind hole and the buried hole are in the same network, it is suggested to cancel the blind hole;
When blind holes and buried holes are in different networks, it is recommended to remove blind holes to avoid them (usually, the ideal value from hole edge to hole edge should be 8mil, and the minimum value should be 6mil).
As for the defects in (b) and (c), it is recommended that customers cancel their blind holes or buried holes, and just keep the through holes, which will affect the function of wireless circuits.
Second, the basic design
1. Panel Size design: no more than 16*18 inch,
Due to the small line width/gap design of HDI board, it is difficult to align, so it is not suitable to design large panel；; At the same time, considering that there are many targets or modules on the edge of HDI board, the edge of HDI board should not be less than 0.8inch as far as possible.
2. The Laser target is designed on the sub-outer layer to facilitate the alignment of the Laser blind hole with the blind hole circuit pad on the sub-outer layer.
3. The pipe holes in the buried hole drilling belt and the through hole drilling belt should be staggered.
3. Conformal Mask film: also known as blind hole pitting film. That is, all blind holes are designed as small gaps with a diameter of 4-5mil, the copper is etched away by the method of line etching, and then the resin layer is opened by a CO2 laser. The selection of D/F is the same as other dry film processes. (Please refer to the attachment for the Conformal Mask process)
4. In order to improve the integration of wiring, all networks are conducted by buried holes and blind holes, and there is no PTH in the whole board. However, PTH is needed for D/F alignment, and only four dry film alignment holes at the edge of the board are not enough. At this time, we need to drill some PTH at the edge of the board and the gong space of the up-panel for D/F alignment. It can be made with reference to S80506AH.
5. Diameter of Laser Blind Hole and its Annular Ring
1) The aperture is generally 4-6mil, and the controllable hole type is the best; Generally, blind holes play a conductive role, and customers have no strict requirements on the aperture.
(When the blind hole is larger than 8mil, mechanical drilling can be considered to reduce the material cost)
2) Tin ring A/R: when adopting new technology, ring 5mil min and pad 4.5mil min should be ensured.
(P.L machine alignment+exposure machine alignment+film deformation +Laser alignment)
When the old process is adopted, ring 4mil min and pad 3.0mil min are guaranteed.
(When blind hole ring can’t meet the above requirements, please communicate with R&D department on how to make it)
3) To ensure sufficient A/R of blind holes, the following methods can be considered:
A) appropriate line shifting; B) Suggest hole removal;
C) reducing the aperture; D) locally reducing the line width;
E) the gap between the wire and blind hole pad shall be 3mil.
Third, the production process
1. Forming method of laser blind hole
1) Direct molding of UV drill (copper and resin are directly penetrated to the sub outer layer by UV radiation)
2) UV drill + CO2 (UV through copper, CO2 laser through resin layer)
3) Uniform mask + CO2 (the copper is etched by etching method, and then the resin layer is opened with CO2)
Among them, (1) and (2) are traditional processes, which have the advantages of accurate alignment, but slow speed and small production capacity,
But (3) is a new process, because of the D / F alignment problem, it is easy to cause hole deviation and hole collapse, but the speed is fast, the production efficiency is high, this process is suitable for mass production
2. Process flow:
Old technological process: the first pressing plate — Gong material — drilling and burying hole — removing glue residue — sinking copper — whole plate electroplating (directly reaching the copper thickness in PTH hole) — burying hole and plug hole — brushing and grinding — L2 / L5 D / F — circuit electroplating (tin plating, no copper plating) — etching — tin stripping — intermediate inspection — browning — second pressing plate (RCC pressing) – Gong material — laser drilling — removing glue residue — Board Electricity — outer layer D / F
The latest technological process:… — first pressing plate — Gong material — drilling and burying hole — removing glue residue — copper deposition — whole plate electroplating — L2 / L5 D / F — circuit electroplating — Corrosion plate — tin stripping — intermediate inspection — browning — buried hole plug hole — (later for outer process) browning — second pressing plate (RCC pressing) – Gong material — blind hole D / F (refer to the attachment) — Corrosion plate — AOI inspection — mechanical drillingAfter drilling, chemical pretreatment is needed to clean the board surface, otherwise the laser alignment and blind hole quality will be affected
1) Buried plug hole
A. Front plug, f / D
a) Ink: hbi-200db96
b) Depth: 100-105%
C) Defect: When the depth of the buried hole plug is insufficient, poor tin plating in the hole is easy to occur due to poor fluidity of the tin bath solution in pattern plating; During etching, etching solution attacks the copper plating in the hole, resulting in no copper in the hole; In addition, when plugging holes, there will be residual ink on the board, so it is necessary to increase the brushing and grinding process to avoid affecting the subsequent electroplating and circuit making. However, in actual production, the quality of brushing and grinding process is difficult to control.
B. Rear plug hole of line
A) ink: shanrong UC-3000-150
B) Depth: 70-100% (it must be strictly controlled, not too shallow or too deep, and the shallowest is not less than 50%)
When the depth is less than 50%, the RCC on the surface will sag, which will easily lead to the outer layer short circuit.
If the depth is greater than 100%, the surface will be raised and uneven, and the inner layer may be deformed after pressing the plate.
C) Hole plugging process: browning and baking at 120℃ for 10 minutes-plugging holes with UC-3000 ink (the depth is controlled at 70-100%)-pre-cure at 60℃ for 30 min (horizontally placed)-one pass of tin spraying UV machine (the speed is 1.5-1.8m/min)-post-cure
Note: I) Browning before hole plugging: As some ink resin will cover the copper surface of the board after hole plugging, the copper surface covered by the ink will not be browned during the subsequent browning before pressing plate, so it must be browned before hole plugging to avoid the laminated explosion of the board after pressing plate without browned copper surface and resin;
Ii) Browning after pressing plate: During the plug hole production operation, the surface of the previous browned layer is easily scratched (the browned layer is extremely thin), and the browned layer may also be damaged after baking. If the browned layer is not done again before pressing plate, the surface adhesion and adhesion during pressing plate will be poor, which may even cause partial delamination.
2) Mechanical drilling first, then laser drilling.
A) firstly, the laser is used to drill the hole and grind the burr mechanically, which may easily lead to the powder falling into the blind hole, and then the process can not completely remove the powder in the blind hole, which may lead to poor electroplating in the blind hole.
B) Some blind holes are too close to the through hole. After laser drilling, the blind holes may be squeezed when drilling through holes, resulting in deformation of blind holes and poor electroplating.
3. Process development trend: Take direct electroplating process, that is, plating hole copper and surface copper to customer requirements at one time, simplifying electroplating process and improving production efficiency; Production of external D/F negative film.
IV. Other inspection items of HDI board making
1. specially check the Ring of VIA hole, and fully consider the selection of its drill nozzle.
2. Check whether there are several blind holes with different diameters in the same board. It is recommended that they be of uniform diameter to facilitate production.
3. Check the blind hole for pad leakage, and analyze whether the blind hole ring is enough.
4. Check the distance from the hole to the periphery, and ask if you can move the hole to avoid hole collapse and copper exposure on the periphery.
5. Check whether the minimum SMD and BGA pad are super powers.
6. Whether there are special requirements for RCC layer thickness, consider the selection of RCC.
