what is tie bar and how it is applied on pcb edge connector
I believe you use tie bars to electrically connect the edge connectors for plating. My colleagues from our manufacturing floor will step in and confirm.
A tie bar is basically a sacrificial connection used for selective plating and to supply current when using electrolytic gold plating. After gold plating, the tie bar gets cut away, leaving just the desired gold-plated features. You typically wouldn’t have to request your manufacturer do apply tie bars, we do it automatically when we have a specific soft or hard gold requirement for instance.
Tie bars are used to electrically connect the edge connector features for Electroplating Nickel / Hard Gold on them. The tie bars are typically 0.01" wide and extend past the board profile. We will add these tie bars and will be removed after the Gold plating process.
When tie bars are used to plate Gold on the edge connectors, the rest of the board can have a different surface finish like HASL, LF-HASL, ENIG, OSP etc.,
With Electroplating process typically the nickel thickness would be 118u" to 250u"and Gold thickness would be 30 - 40 u". Hard gold is plated onto the PCBs after the solder mask process and before applying the surface finish to the rest of the board.
Electroplated gold is thicker and harder which makes it ideal for edge-connector contacts for PCBs as they would be repeatedly plugged in and removed.
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Thanks for the insights! I understand that tie bars are used for plating purposes and are later removed. Could you clarify if there are any design considerations or potential drawbacks related to the use of tie bars, particularly in high-density designs or when working with very fine-pitch edge connectors? Are there cases where alternative techniques are preferred for edge connector plating?
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There are no layout concerns that I know of regarding Tiebars. To be honest, having designed at least the occasional board since 1980 I only learned about “Tiebars” a few years ago, and didn’t learn the name “Tiebar” until about six months ago. The process is done by manufacturing during the creation of the board. There may be geometries or issues that cause problems, but I’ve never heard of any so I assume the process is straightforward enough not to be concerned. If you think you might have an issue you can check IPC or you could call our manufacturing experts.
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