Flax residue with high heat resistance
Please note that if you reduce the rotation speed of the fan, it may lead to a failure unless you check with the manufacturer in advance.
To reduce the fan speed and suppress the deterioration of flux, increase the conveyor speed or turn off the extra heater at the top to make a compact temperature profile.
Even in actual market troubles, insufficient wetting, voids, and immo soldering conditions occur in the shadows of parts and on boards on which large and small parts are mounted at high density.
However, these may be overlooked in the inspection due to the fine solder fillets.
Fine land soldering
The flux is about half the volume of the printed solder.
If the preheat is lengthened (the amount of heat is increased), the flux deteriorates and its effect is lost, and the joining quality such as insufficient wetting and voids deteriorates.
Parts are attached to the melted solder.
Due to deterioration of the flux, there is no fluidity of the solder, and the spread is insufficient.
The thick solder under the parts may be due to the deterioration of wettability, and the parts may be attached to the melted solder.
It is necessary to make an observation judgment by matching the temperature profile and fillet condition.
Wetness of the above chip parts is good, but this is simply due to the large amount of solder.
The lack of fillet luster indicates that the cooling rate is delayed due to excessive heat.
Despite the large amount of solder, the tip of the fillet is unmelted and the entire fillet is undermelted.
When the flux deteriorates, the solder particles oxidize and become incompletely melted, creating voids that cannot be confirmed from the outside.
Even in this state, the tensile strength is considerable, so it does not break down immediately.
However, when electricity flows and heat is generated, it causes deterioration of strength and leads to failure.
The surface of the fillet is completely melted, but the inside of the fillet has many voids due to lack of fluidity.
With a long temperature profile (large amount of heat), even if the solder is melted, if the flux deteriorates, a sufficient alloy layer will not be formed, causing poor bonding.
Since connectors etc. have a large number of pins, the tensile strength is moderate.
Since it is difficult to evaluate, please check the peeling strength one by one.
Examples of improvement in wettability
By suppressing the flux deterioration due to preheating, the wetness of the solder is improved, the parts are adsorbed on the land side, and the voids are also improved.
If good wettability can be obtained, the component leads will be attracted to the land side, the solder under the component will be thin, and the bonding strength will be strong.
Improved temperature profile
Wetability is improved by melting the solder without deteriorating the flux.
It is often judged that the unmelted solder is due to lack of heat due to the large size of the parts, but it is due to the heat dissipation phenomenon from the pattern of the board, and it is completely suppressed by raising the lower heater to suppress the heat transfer. It’s melting.
Wetness cannot be obtained by simply melting the solder.
An example of cutting the preheat
If the flux is degraded by preheating, the solder will not melt even if the top temperature is raised.
With proper preheating, the solder will melt sufficiently even if the top temperature is around 230 degrees.
Effect of hot air
Even on the same board, the effect of hot air differs between the slits and the edges and center of the board.
Inspection points may also need to be considered depending on the placement of parts.
There is no lack of heat.
Land solder with a large amount of solder is completely melted, but land solder with a small component lead is unmelted. The cause is overheating of the preheat.
Even fine parts such as the 0402 chip can be self-aligned if the solder can be melted before the flux deteriorates.
The technical information posted here was written by Mr. Kazuo Kawai, an implementation advisor, at the request of our company.
If you have any questions regarding the articles listed, please contact Kawai Advisor via our company if you contact us from our website.
Please note that it may take some time to respond depending on the content of your inquiry.