Recently I posted in the group with the wrong format, apologies for that! Reddit was preventing me to post again with the same username, so posted with another one.
We are facing issues in our production related to some unknown invisible residue that comes on top of the PCB pad during SMT assembly. The pad has an ENIG coating currently and the pogo pin has following specs:
- Contact head C3604 brass alloy, electroplated with 50-80u nickel.
- The bushing is made of C3604 brass alloy, electroplated with 50-80 μm nickel.
- The spring is made of SUS304 stainless steel.
- The elastic force is 85gf ± 20% at 1.5 strokes.
The product we have consists of a battery pack that slides inside the housing and comes into contact with the PCB using a pogo pin that sits on this pad (see the images). Due to this residue (we suspect its no-clean flux) the connection between the pad and the battery pack sometimes
deteriorateand flickers.
The solution we found was to clean it with Isopropyl Alcohol (IPA), but we don`t want to include this extra step at the end, if we are already using no-clean flux in the assembly.
So we came up with following solutions of which all have some pros and cons. It would be great if someone can recommend how to get rid of this residue or counter it with either of the solutions:
- Hard gold: better connectivity, should protect against Oxide but not flux residue
- Solder tinning:
- cost effective
- better contact
- oxidation issue
- can wear out over time
- inconsistency/repeatablility issue.
- Replacing pad with Spring contact:
- Independence from the residues
- Better pressure and contact handling
- PCB and BOM needs to be adjusted
- spring contact compatibility with the pogo pin
- Changing Pogo design pin to crowned Pin
- Less change required, fairly easy
- Not sure if new one can penetrate the oxide/flux layer, trial and error required
- May be have an increase spring force than 85kgf
We are more biased towards the change of pogo pin to crowned pin as its much easier and should penetrate better. But its still risky as the surface has this unknown residue and we are shooting in the blind.
Thanks in Advance
