Dear Members of the forum, my name is Lorenzo and I am a new member of the Forum. Nice to meet you!
I have made a small, dual layer and circular PCB designed in order to be placed beneath a stack of 3 LR44 coin cell batteries. Its size is slightly bigger than the LR44 dimension.
On the upper side and in the center of the PCB, there is just a pad in order to guarantee the electrical connection with the coin cell. On the lower side of the PCB there is an MCU and few passive components.

According to your experience, do you think that its close position to the coin cells and/or the high density of the components underneath would be a roadblock for the PCB market/production? Would this kind of design pass the required certifications?

Thanks for any suggestion.

 

Dear Members of the forum, my name is Lorenzo and I am a new member of the Forum. Nice to meet you!
I have made a small, dual layer and circular PCB designed in order to be placed beneath a stack of 3 LR44 coin cell batteries. Its size is slightly bigger than the LR44 dimension.
On the upper side and in the center of the PCB, there is just a pad in order to guarantee the electrical connection with the coin cell. On the lower side of the PCB there is an MCU and few passive components.

According to your experience, do you think that its close position to the coin cells and/or the high density of the components underneath would be a roadblock for the PCB market/production? Would this kind of design pass the required certifications?

Thanks for any suggestion.

Your description of what you have done is not very clear, what is preventing the cells from becoming displaced – potentially causing short circuits once they are randomly placed on the PCB?

In terms of regulatory compliance, your circuit design should be such that under normal operation and single fault condition, the charge and discharge battery specification is not exceeded.
Bear in mind that such non-rechargeable batteries normally have a maximum abnormal charge limit.

Circuit analysis can be used to demonstrate compliance, with the battery replaced by a low impedance ammeter when assessing maximum fault charging current and a voltage supply (with a low internal resistance) when assessing maximum fault discharging current.

Single fault conditions to be applied include the short circuit/open circuit of any component (applied one at a time).
Any PCB tracks spaced less than 0.4mm apart can be short circuited as part of the above faults.

 

Your description of what you have done is not very clear, what is preventing the cells from becoming displaced – potentially causing short circuits once they are randomly placed on the PCB?

Basically, there's a cylindrical battery holder that keeps in place a stack of 3xLR44 batteries. The pcb acts as a sort of base for this battery holder. The diameter of the PCB is similar to the LR44 diameter. As you can imagine the pcb is small but I was able to place and connect all the components needed. Hope now it is clear, if not I can attach a draft image.

In terms of regulatory compliance, your circuit design should be such that under normal operation and single fault condition, the charge and discharge battery specification is not exceeded.
Bear in mind that such non-rechargeable batteries normally have a maximum abnormal charge limit.
Circuit analysis can be used to demonstrate compliance, with the battery replaced by a low impedance ammeter when assessing maximum fault charging current and a voltage supply (with a low internal resistance) when assessing maximum fault discharging current.
Single fault conditions to be applied include the short circuit/open circuit of any component (applied one at a time).
Any PCB tracks spaced less than 0.4mm apart can be short circuited as part of the above faults.

Thanks for you information, do you have any related link or document I could refer to?

 

Basically, there's a cylindrical battery holder that keeps in place a stack of 3xLR44 batteries. The pcb acts as a sort of base for this battery holder. The diameter of the PCB is similar to the LR44 diameter. As you can imagine the pcb is small but I was able to place and connect all the components needed. Hope now it is clear, if not I can attach a draft image.


Thanks for you information, do you have any related link or document I could refer to?

The requirements I have applied are typical of product safety standards, but specifically I have used IEC/EN 60950-1.

To assist your understanding I have attached a typical BIOS battery protection circuit.

V1 is the coin cell providing the back-up voltage Vbat (3V) to the BIOS chip via D1 and R1.

With the coin cell having a specified maximum abnormal charge of 10mA, we require this limit to be met under single fault conditions.

With the battery fully discharged (and replaced by an ammeter), if the resistor R1 fails short circuit, diode D1 will prevent any current charging the battery.

If diode D1 fails short circuit, then the abnormal charge current will be Vbat (3V) / R1; therefore in this example the minimum value for R1 is 300 ohm.

The above example shows how circuit analysis can be used to demonstrate compliance.