Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Not something like datasheets, but I have some ideas. Very few manufacturers offers data about humidity in the datasheets. Basically, humidity does not affect the plastic and non-conductive areas, only the metalic ones. In time, and in high humidity environments, oxidation occurs (the structure of the pin is also important - composition, coatings, etc.) , and becasuse of this, most probably you won't be able to solder the smd's in automatic line processes. The humidity affect the thermal soldering profile of the device. Simply, the soldering metal will adhere to some pins and to others, not. This will happen mostly for high pin count smd. However, if you plan to solder smds manually, this will not be a problem. Few seconds more with the soldering iron on the pins will resolve this problem.
Don't you think the worst problem caused by humidity in
BGA's and alike are delamination of the "pcb" that make
up the package?
When exposed to humidity, some water slowly diffuses inside
the package. Later on, you decide to solder your apparently
intact and shiny chip but the quick temperature rise
of reflow boils this water to very high vapour pressure since
it cannot escape quickly enough of the package.
In the worst case, this pressure is higher than what the
package can cope with and it creates a hole (delaminates)
to escape to free air.
If this happens and you are sure about gradient and thermal profile of the oven, the only cause can be the oxidation of the pins for the SMD devices.
Take care at this:
- If the components not soldered are randomically distributed the reason could be oxidation ofthe pins;
- If are not soldered some specific areas the reason could be the thermic profile of the oven ( also some times due to the PCB )
In the old days military products which had high reliability requirements were required to have metal, glass, or ceramic packages. Plastic packages did not seal well on the leads and allowed moisture to enter and corrode the connecting wiring inside the transistor or IC packages.
kot_b, humidity may be one reason, but other reasons can conduct to results like this, for example, in the proximity of the areas where the chip can't be soldered exists some devices with big volumes, which absorb heat much slower, thus conducting in a degradation of the temperature variation profile in the surrounding area.
The effect in oven reflow is called popcorning and can be expirienced with any device in the reflow oven.Specialy sensitive devices are devices which are tin and have many pins QFP etc. The problem is treated by IPC and it is not trivial.
Greetings
Dragan
If you are worried about humidity affecting your components, then take some steps to prevent it. Use decent controlled storage etc, dont just leave them out on open shelves.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
