Production process - for multilayer PCBs

There is no such thing as a standard printed circuit board. Each PCB has a unique function for a particular product. Therefore, producing a PCB is a complex process of many steps. This overview covers the most important steps when producing a multilayer PCB.
 
When you order PCBs from the NCAB Group, you are buying quality that pays for itself over time. This is guaranteed through a product specification and quality control that is far more stringent than other suppliers, and ensures that the product delivers what it promises. In the production flow below you can see where the NCAB process is unique or goes beyond the IPC standard.
  • NCAB Group PCB Specification is applied
  • NCAB Specific production routines
  • Board manufactured using NCAB approved equipment
  • NCAB employees and dedicated teams
  • Clean room
  • All our factories are ISO 9001 and ISO 14001 certified
1. PPE - Pre Production Engineering

Customer supplied data (gerber) is used to produce the manufacturing data for the specific PCB (artworks for imaging processes and drill data for drilling programs). Engineers compare demands/specifications against capabilities to ensure compliance and also determine the process steps and associated checks. No changes are allowed without NCAB Group permission.

NCAB ADDED VALUE
With 200+ evaluated and approved factory
pre-production engineers
handling your
data, NCAB Group builds in security from the
very start of the process.

2. Material issue

Material of various types are received from approved sources and held in controlled environments until required. Using FIFO systems, specific material is released into production for a specific purchase order with base materials cut to the required sizes. All materials used can be traced back to their manufacturing batch.

NCAB ADDED VALUE
We only use internationally known base
materials – we don´t allow ‘local’ or
unknown brands.

3. Inner layer

Stage 1 is to transfer the image using an artwork film to the board surface, using photosensitive dry-film and UV light, which will polymerise the dry film exposed by the artwork.
 
This step of the process is performed in a clean room.
 
 

4. Inner layer etch

Stage 2 is to remove the unwanted copper from the panel using etching. Once this copper has been removed, the remaining dry film is then removed leaving behind the copper circuitry that matches the design.
 
 
 
 

5. Inner layer AOI

Inspection of the circuitry against digital “images” to verify that the circuitry matches the design and that it is free from defects. Achieved through scanning of the board and then trained inspectors will verify any anomalies that the scanning process has highlighted. NCAB Group allows no repair of open circuits.

NCAB ADDED VALUE
All PCB’s are tested using NCAB approved
equipment
and no track welding or open
circuit repair is allowed. This provides
increased reliability
as there is no risk of
repair failure, nor will this impair signal
integrity.

6. Lamination

The inner layers have an oxide layer applied and then “stacked” together with pre-preg providing insulation between layers and copper foil is added to the top and bottom of the stack. The lamination process uses a combination of specific temperature, pressure for a specific time to allow the resin within the pre-preg to flow and bond the layers together to form a solid multilayer panel.

7. Drilling

We now have to drill the holes that will subsequently create electrical connections within the multilayer PCB. This is a mechanical drilling process that must be optimised so that we can achieve registration to all of the the inner layer connections. The panels can be stacked at this process. The drilling can also be done by a laser drill, which is the case in the attached production video.

NCAB ADDED VALUE
All PCB’s are drilled using NCAB approved
equipment which offer the best performance
such as positional accuracy.

8. PTH - Plated Through Hole

PTH provides a very thin deposit of copper that covers the hole wall and the complete panel. A complex chemical process that must be strictly controlled to allow a reliable deposit of copper to be plated even onto the non-metallic hole wall. Whilst not a sufficient amount of copper on its own, we now have electrical continuity between layers and through the holes.
 
 
 
 

9. Panel plating

Panel plating follows on from PTH to provide a thicker deposit of copper on top of the PTH deposit – typically 5 to 8 um. The combination is used to optimise the amount of copper that is to be plated and etched in order to achieve the track and gap demands.

NCAB ADDED VALUE
NCAB provides through hole
plating of 25um nominal, as
standard (equates to IPC class 3).
This is 25% more copper than
achieved with IPC class 2
and
provides greater reliability of the
via structure and improved z-axis
expansion performance.

10. Outer layer image

Similar to the inner layer process (image transfer using photosensitive dry film, exposure to UV light and etching), but with one main difference - we will remove the dry film where we want to keep the copper/define circuitry - so we can plate additional copper later in the process.
 
This step of the process is performed in a clean room.

11. Pattern plate

Second electrolytic plating stage, where the additional plating is deposited in areas without dry film (circuitry). Increases the plating thickness to meet demands including NCAB Group demands with and average of 25um / min 20um through the hole. Once the copper has been plated, tin is applied to protect the plated copper.

NCAB ADDED VALUE
NCAB provides through hole plating
of 25um nominal, as standard (equates
to IPC class 3). This is 25% more copper
than achieved with IPC class and provides
greater reliability of the via structure and
improved z-axis expansion performance.

12. Outer layer etch

This is normally a three step process. The first step is to remove the blue dry film. The second step is to etch away the exposed/unwanted copper whilst the tin deposit acts an etch resist protecting the copper we need. The third and final step is to chemically remove the tin deposit leaving the circuitry.
 
 

13. Outer layer AOI - Automated Optical Inspection

Just like with inner layer AOI the imaged and etched panel is scanned to make sure that the circuitry meets design and that it is free from defects. Again no repair of open circuits are allowed under NCAB Group demands.

NCAB ADDED VALUE
All PCB’s are tested using NCAB approved
equipment and no track welding or open
circuit repair is allowed.
This provides
increased reliability as there is no risk of
repair failure, nor will this impair signal
integrity.

14. Via hole plugging

Using soldermask ink or epoxy resin and a prepared stencil, with holes in the stencil that align with the via holes we wish to plug, we use a screen printing process to push ink or resin into holes. Unlike soldermask we are trying to push ink through the holes in the PCB and judge quality based upon the NCAB Group demands of ≥ 70% fill.
 
This step of the process is performed in a clean room.

NCAB ADDED VALUE
With ≥ 70% soldermask fill on type
VI via holes, NCAB provides less
risk of via holes causing rejection
during assembly.

15. Soldermask

Soldermask ink is applied over the whole PCB surface. Using artworks and UV light we expose certain areas to the UV and those areas not exposed are removed during the chemical development process – typically the areas which are to be used as solderable surfaces. The remaining soldermask is then fully cured making it a resilient finish.
 
This step of the process is performed in a clean room.

NCAB ADDED VALUE
NCAB defines soldermask thickness, IPC
does not.
With ≥ 5um on the knee of the track
and between 10-30um on the surface NCAB
PCB’s offer improved electrical insulation and an
improved resilience to chemistry or mechanical
force that could cause loss of soldermask.

16. Surface finish

Various finishes are then applied to the exposed copper areas. This is to enable protection of the surface and good solderability. The various finishes can include Electroless Nickel Immersion Gold, HASL, Immersion Silver etc. Thicknesses and solderability tests are always carried out.
 
 

17. Profile

This is the process of cutting the manufacturing panels into specific sizes and shapes based upon the customer design as defined within the gerber data. There are 3 main options available when providing the array or selling panel – scoring, routing or punching. All dimensions are measured against the customer supplied drawing to ensure the panel is dimensionally correct.

NCAB ADDED VALUE
All PCB’s are profiled using NCAB
approved equipment which offers the
best performance such as positional
accuracy.
Default tolerances are applied
to all designs if none are defined on the
procurement documentation.

18. ET - Electrical Test

Used for checking the integrity of the tracks and the through hole interconnections – checking to ensure there are no open circuits or no short circuits on the finished board. There are two test methods, flying probe for smaller volumes and fixture based for volumes.

NCAB ADDED VALUE
NCAB do not allow no track
welding or open circuit repair.

19. Final inspection

Visual checking the PCB against acceptance criteria and using NCAB “approved” inspectors. Using manual visual inspection and AVI - compares PCB to gerber and has a faster checking speed that human eyes, but still requires human verification. All orders are also subjected to a full inspection including dimensional, solderability, etc.

NCAB ADDED VALUE
Each PCB is inspected against the 100+
points
as defined in the NCAB product
specification and every batch is subject to
a full evaluation prior to shipment to ensure
the PCB’s are produced to the highest
standard. Our onsite NCAB QC teams
oversee the verification processes.

20. Packaging

Boards are wrapped using materials that comply with the NCAB Packaging demands (ESD etcetera) and then boxed prior to be being shipped using the requested mode of transport.