Wearable product implementation issues 1

In wearable products, not only the board but all the parts are small, and the soldered terminal part (land part) is small and narrow to the limit of visual inspection.
It can be mounted without any problem at a mere experimental level, but in an actual mass production line, management technology such as warpage of surrounding parts and sheet boards is required.
At the mass production site of FPC, it can be seen that it is discarded because there is no room for individual correction and analysis due to the production volume and delivery date.
 
Mounter makers can handle up to 0201 chip size.
For solder supply, the dispenser can handle all sizes, but considering productivity, we want to print all at once.
 
The mask maker proposes printing with a mask with a thickness of 40 to 60 µ in the 0201 chip size class, but it depends on the design whether it can handle the parts leads around it that are mounted at the same time.
It seems to be difficult with a metal mask with a thickness of at least 40µ.
 
Solder makers offer particle size type 6, but type 6 is so fine that it has a lot of oxides on the surface and even if it can be printed, there is still a problem with wettability.
Especially in the normal temperature profile, the flux deteriorates and the bonding is performed in a state where it is poorly melted or adheres to the melted solder.
In addition, there is a problem of voids, and the quality of the products to be carried is very unstable.
 
In the old overseas mobile phones, after mounting CSP on the FPC, it was hardened with underfill, but there were many defects in the market and it was a problem.
Since the production volume is an order of magnitude higher, it was in a state of being discarded.
 
If it is a mass-produced product, it can be handled even if the initial investment is a little large, but it is difficult to invest at the stage where the lot is small, and if possible, mass production with the current equipment is required.
In January, the Kyoto Mounting Technology Study Group received a 0201 chip from the manufacturer and conducted all manual experiments.
 
The metal mask was 60µ and the solder was printed using type 6 and type 4.
The solder maker wanted to support nitrogen reflow, but is experimenting with atmospheric reflow.
Wetability varies depending on the flux of the solder used, but it is especially important to create a temperature profile.
Since the flux deteriorates immediately with fine solder particles and amount, the solder will not melt unless a temperature profile (upper and lower heater and fan rotation speed) that melts the solder without deteriorating the flux is devised.
Even if it melts, fine solder balls are generated and insufficient wetting occurs.
 
Mass production of wearable products has various problems, including handling and product management, due to the miniaturization of parts.
 
Parts mounting
The mounting of parts has almost been completed by the mounter manufacturers.
 
Solder supply
Although it is possible to provide type 6 fine particles for solder, the problem is the selection of the flux used.
When the solder particles become finer, the oxide on the surface of the particles increases, and the effect of the flux is reduced by that amount, which reduces the ability (wetting property) to remove the oxide on the surface of the parts and substrate land. Become.
Since the flux occupies about half of the supplied solder amount, if the amount of solder is small, the amount of flux is further small and deterioration at the preheat stage progresses, causing melting inhibition of the solder particles.
 

 
In A, the entire solder is covered with flux, so there is no problem with reflowing as it is.
B needs to verify the temperature profile.
C needs to change the flux.
 
Solder supply method
A dispenser can be used to supply solder in a sufficiently stable manner.
However, with the sheet board, the problem of productivity (tact) remains.
 
At present, it is proposed that the thickness of the metal mask of the land part of the fine parts is about 40μ or 60μ for batch application with a printing machine, so it is possible to do it by simple experiment, but solder supply to the subcutaneous parts to be mounted at the same time. The problem remains in quantity.
 
Assuming from the product size, if the mask thickness is about 80µ to 100µ, it seems that it is possible to apply all parts at once.