how to solve the solder joints not shiny?

Question

I have met a problem, need your help. I had used Sn62Pb32Ag2 (liquid temperature is 179℃)solder paste to solder components for many years,solder joints always are shiny. but recently,when I used it to solder AgPa alloy finished resistores,
after reflow soldering ,the solderjoints were not shiny as they were supposed to be. I have tried many reflow profiles, the peak temperature(TP) of the solder joints from 222℃to 210℃,time of temperature higher than 179℃ are range form 60s~100s,some time ,the time of temperature higher than 215℃ reach 20s,higher than 220℃ time reached 6s. but all solder joints are not shiny as normally.

Answer 1

It is a myth that solder joints should be shiny, and the surface appearance does not tell you anything about the quality of the electrical connection.

There are many things that can effect the shinyness of the joint, including but not limited to: type of metal used, type of flux used, age of the flux, soldering iron temp, how long it was at an elevated temp, how quickly it cooled down, how evenly it cooled down, etc.

When evaluating the appearance of a solder joint I look for these things:

1. Did the solder properly wick or wet the mating surfaces?
2. Does the solder look even or consistent in how it flowed over the joint?

That's it! If I want to be extra sure I will sometimes push sideways on a pin of a TSOP or similar inverted gull-wing style chip with a very fine dental pick. If the pin moves then it wasn't soldered correctly.

Answer 2

There are known issues in soldering Palladium alloy solder "tinned" parts.
Reported experiences are significant enough that you probably need to ask for specific advice or carry out tests to see if joint nature will suit you long term.

Parts usually have a "use before date" typically one year, and user reports suggests that results do vary with age.

Whether results are "bad" or just "different" seems to vary with source, and even formally conducted tests can achieve results which the testers certify are what they saw but which they also say differ from other reports.

Comprehensive TI Palladium alloy soldering report.
Evaluation of Nickel/Palladium-Finished ICs With Lead-Free Solder Alloy.
This is lead-free focused but Pb based also mentioned and it seems closely related to your issues.
Useful photos and tests. Thy are more concerned with pull off strength and observable wetting performance. Liable to be useful.

Reflow issues related user discussion but probably overlaps your area usefully.
Ag/Pd termination reflow soldering issues
and here.

NOT of direct relevance to appearance but reason for use of Pa discussed.here

Jewelery soldering applications such as here suggest surface discolorisation which can be wholly removed by buffing. It would be interesting to know if your joints improved when brushed with a stiff brush.

Another jewellery soldering application same need for cleanup.

IEEE abstract. Some posible use.