Special Ordering Guide for FPC Gold Finger Stiffeners

After designing the gold fingers on your flexible printed circuit (FPC) to the connector specifications and determining the required thickness, you may find the following options on the JLCPCB order form confusing: “Gold Fingers,” “Gold Fingers Thickness,” “Stiffener,” and “Polyimide Thickness.” Aren’t gold finger stiffeners simply polyimide stiffeners? Why do I also need to specify whether the FPC has gold fingers and enter their thickness? How should I select the correct order parameters?

This guide explains why these options are provided and how to place an order for this type of FPC.

FPC gold finger stiffeners are typically used to meet the strict thickness requirements of the connector into which the fingers are inserted. The critical parameter for proper connector operation is therefore the total thickness of the stiffened gold finger region, measured from the plated contact surface to the outer surface of the stiffener beneath it.

For this reason, we have added the “Gold Fingers” and “Gold Fingers Thickness” options. After selecting “Yes” under “Gold Fingers,” enter the required total thickness in the “Gold Fingers Thickness” field.

You can also use “the PI Calculator” to calculate the required polyimide (PI) stiffener thickness for the gold fingers yourself. Enter the dielectric thickness, number of layers, FPC thickness (excluding stiffeners), whether copper is present on the circuit layer on the stiffener side of the gold finger region, and the coverlay color for your order. The calculator will recommend a PI stiffener thickness for the gold fingers. Select this value under “Polyimide Thickness” when placing your order. If your design also includes PI stiffeners outside the gold finger region, remember to select their thicknesses as well.

To further ensure proper connector fit, we give the total thickness you specify the highest priority when selecting the stiffener thickness beneath the gold fingers. Even if you have not calculated the correct stiffener thickness, we can use the key parameter you provide—the required total thickness of the gold finger region—to select a suitable stiffener and ensure reliable insertion into the connector.

You must also select the types and thicknesses of any stiffeners outside the gold finger region. These stiffeners will be manufactured according to the thickness values you select.

Gold Finger Stiffener Calculator
https://jlcpcb.com/gold-fingers-pi-thickness-calculator?stencilLayer=2&stencilPly=0.11&fpcColor=Yellow&type&goldfingerThickness=null

For guidance on selecting stiffeners and recommended layer naming conventions, see our article below.
https://jlcpcb.com/help/article/fpc-stiffener-emi-guide

Additional Questions and Answers

Q1

My FPC has both gold finger stiffeners and PI stiffeners beneath components. The required thicknesses are 0.3 mm for the total thickness of the stiffened gold finger region and 0.225 mm for the PI stiffeners in the component region. How should I place the order?

A1

1. Select “Yes” under “Gold Fingers” and enter the required total gold finger thickness.
2. Select “Polyimide” under “Stiffener,” then select both 0.225 mm and 0.2 mm (the value calculated using “the PI Calculator”) under “Polyimide Thickness.” Specify the stiffener thickness for the component region in your design files or in the order remarks. Ideally, follow the naming conventions in our article at https://jlcpcb.com/help/article/fpc-stiffener-emi-guide and explicitly draw the outline of each corresponding stiffener region.

You can annotate the Gerber files as shown below.

Q2

If my FPC has both gold finger stiffeners and PI stiffeners beneath components, and both thickness requirements are 0.25 mm, how should I place the order?

A2

1. Select “Yes” under “Gold Fingers” and enter the required total gold finger thickness.
2. Select “Polyimide” under “Stiffener,” and select only 0.25 mm under “Polyimide Thickness.” Specify in your design files or order remarks that the PI stiffener thickness beneath the components is 0.25 mm. Ideally, follow the naming conventions in our article and explicitly draw the outline of each corresponding stiffener region.

Q3

My FPC has both gold finger stiffeners and PI stiffeners beneath components, with thickness requirements of 0.25 mm for the gold finger region and 0.15 mm for the component region. It also includes steel stiffeners with thicknesses of 0.1 mm and 0.2 mm. How should I place the order?

A3

Follow the approach in Q1. The “Stiffener” field allows you to select multiple stiffener types at the same time. Clearly specify the region and thickness for each stiffener in your design files or order remarks.

Q4

My FPC has four layers and a board thickness of 0.3 mm. I still need to precisely match the thickness at the gold finger region. How should I place the order?

A4

Our gold finger stiffener calculator does not currently support multilayer FPC calculations. However, the same principle applies: select “Yes” under “Gold Fingers” and enter the required total thickness of the gold finger region after stiffening. Clearly specify the stiffener regions and thicknesses in your design files or order remarks, then select a thin stiffener option (such as 0.1 mm) when placing the order. We will select a suitable gold finger stiffener to meet your thickness requirement.