Application Example Four Layer Immersion Gold Control Board
An industrial control board carrying a fine pitch processor, an array of board-to-board connector footprints and a BGA site, built on four layers with an immersion nickel gold finish.
What Had To Be Solved
Boards of this shape have two competing requirements. The fine pitch footprints need a perfectly flat pad surface or parts will not self-align during reflow. The board also has to pass emissions testing in an electrically noisy cabinet, which means the return path for every fast signal has to be short and continuous.
Customer name, order volume and project dates are confidential and are not published.
Four Things That Had To Stop Happening
- Fine pitch parts tipping on a crowned HASL surface
- Radiated emissions failures traced to long return paths
- Escape routing that will not fit without growing the outline
- Boards stored between fabrication and assembly, with pads oxidising in between
How The Board Answers Them
Four layer construction puts a continuous ground plane directly beneath the routing layers and gives the supply rails their own copper. Immersion gold keeps every pad flat and oxide-free. Minimum trace width and space of 0.075 mm let the escape routing from the fine pitch footprints finish inside the original outline.
How The Board Is Produced
Each stage below runs inside our own plant in Fuyong, Shenzhen.
Stage 1
Inner layers imaged and etched, then checked before lamination
Stage 2
Stack-up pressed on the MLB laminator
Stage 3
Drilled on CNC drillers, then plated through to a 0.025 mm wall
Stage 4
Outer layers imaged, etched and solder mask applied
Stage 5
Immersion nickel gold applied across the board
Stage 6
Routed to outline at ±0.10 mm, then open and short tested at 50 to 300 V
Where Coordination Happens
The bare board and the assembly are handled by the same plant, so the surface finish, the panel format and the reflow route are decided together rather than negotiated between two suppliers. There is no shipping leg between fabrication and assembly, and no handover where damage or delay can enter.
Components are either bought here on a turnkey basis or consigned by you, with the split marked line by line on the bill of materials.
What Is Verified
- Inner layer inspection before lamination, because buried defects cannot be repaired
- Open and short testing at 50 to 300 V on every board
- Hole resistance verified below 300 Ω at normal condition
- Isolation resistance verified above 1012 Ω at normal condition
- Warpage held at ≤0.75% across the panel
Where This Board Stands Today
The board is produced as a standard catalogue item. Layer count, surface finish and the process tolerances above are the published figures for our rigid line.
Boards In The Same Family
Other catalogue items built on the same line to the same published tolerances.
Double Sided FR4 Board With Lead Free HASL
Four Layer Immersion Gold Board For Dense SMD Routing
Six Layer Board With Lead Free HASL For Larger Controllers
Eight Layer Board With Electroplated Gold For Contact Surfaces
Questions About This Example
Can you tell me who this board was built for?
No. Customer names, order volumes and project dates are confidential and are not published. What is published is the board, its family and the process tolerances behind it.
Can you build the same board for me?
The board shown is a rigid pcb catalogue item. Send your own files and we will quote against the same process and the same published tolerances.
What if my requirement is close but not identical?
That is the normal case. The capability tables define the envelope, and anything inside it can be built. Anything outside it we will tell you about before tooling.
Which industries does this apply to?
This example sits in industrial control, but the same board family is used across the other sectors in the catalogue as well.
Bring Us A Board With The Same Problem
Send the files and describe what has to stop happening. We will tell you which family and which tolerances solve it before quoting.