Joining Flashcards
What are the diffences between welding, soldering brazing and adhesive ?
- Welding, melting the materials
- Soldering and brazing, diffusioncauses intermetallic zone (only the solder in the mittle is melted)
- Adhesive, Adhesive in melted state come slose anoth for intermolecular forces to act.
what is solddering and brazing?
- joining of metallic parts through addition of a filler material, the solder
- The solder is melted and has a different compasition than the base material
- The melting temp of the solder is lower than the base materials
- The base material is not melted
Soldering
- Melting point below 450°C, often 200°C
- Can withstand some machanical load
- Used mostly for electrical and therman connections
- Laso plumbing (copper, brass)
Brazing
- Melting point of solder (filler material) over 450°C, often 500-600°C
- Typically for much higher machanical loads yield strength 100Mpa
- Typically slearence 0,025-0,25 mm
How is the general process for soldering and brazing?
- Heating of the soldering position or the whole parts to above the melting point
- Fluxing: removes oxides, prevents oxidation, increases wetting
- application: fluid, integrated inside solder wire
- Solder application
- Three ways:
- External applicatio, solder wire
- Pre-placed, paste
- Solder pot, dipping
- Wetting of the solder
- Difussion: solder and base material, e.g. if you have copper and Sn-Pb as solder the Sn and Pb is the disfussion layer
- Three ways:
- Cleaning
- Heating of solder: Usally to the autectical point beacuse it gives good composition of the solder
What are the new alternatives for sodering material?
Pb-Sn was often used before Pb not alod anymore
New:
- Sn-Ag-Cu
- Sn-Cu
- Sn-Ag
Problems with the new:
- Higher temperatures (melting point)
- Quality: more porosity
- Higher cost
- Production system changes
What is important to think about in the design?
- Big joint area so that it can take more shear load
- Same thickness of the materials to be joined
- Have sufficient bonding
What adhesives types is there ?
- Molecular (or dispersive)
- Attraction between molecules when “close enough” typically 5Å (<1nm)
- Van der wahl´s forces
- the adhesives must be a liquid to come this close
- The adhesive must be able to wet the material
- Mechanical
- Locking by fillinf pores and clinching to irreagularties
What is the surface tension and how do it affect the wetting?
A liquid material will wet a solid material with a higher surface tension
- . Hard to get semthing to wet on teflon that has very low tension so to be able to assamble teflon at tha pan the teflon nees to wet the iron.
What can the addehsives be made of?
- natural
- Synthetic: most common
- Thermoplastic
- Thermosets (strongest)
- Needs curing to harden
- mix with katalysator (2K)
- Heating
- UV
- Needs curing to harden
What are the advantages of adhesives?
- Many materials and combinations of materials can be joined
- Large area bonding
- Sealing and electrical insultion
- Low temperature preocess
- There are adhesives that are flexible = tolerant to cycle loads
- Quite simple joint design
What are the disadvantages with adhesives?
- Lower strength that other joining methods
- Ahesive must ve chosen to be compatible with joined material
- Service temperature is limited
- Less available technologies for non-destructutive tests/inspection
- bad for environment (thermosets especially)
- Ca be dangerous to breath in
what is a printed curcuit board (PCB) ? what is its purpose
its a plat where components are placed on, the purpose is to have electrical conection, heat transfer or machanical joining
How can the componet be placed on the board ?
can be places single sided and then the conductive trakc is only on the down side. It can be places double sided then the conductive track is on both top nad bottow and inbetween.
It cn be places whrough hole (PTH)
or Surface mount tecknology (SMT)
placed on pads. Area effective in place of hades, component placement more easy.
The components can be plased with hand soldering how is that process?
- heating of PTH or PAD and componet lead with the iron
- Heating time dependent on amount of Cu in lead and nearby Cu layers in PCB
- Form up-and/or down side depending an accessibility
The componets can be places with wave soldering how does that process work?
- The PCBs are moving on a band that is angled
- Mainly for PTH mounted componets on upper side
- SMT component om down side
- first fluxing: foam or spray
- then pre heating: activate fluc and avoid therman shock
- Solder wave: the surface of the solder is movin in smal waves so that the solder rises in pTH between lead and wall through capillary forces.
What is common method for SMT mechanisation ?
- Solder paste application
- screen printing
- Dispensin
- Component placement
- Sutomatic “pick and place”
- Soldering : “Reflow”
- Convection over or
- vapour phase oven
Stencil or syring dispensing
How does resistanse spot welding work? and what can happen if it goes wrong ?
Two plates are joind together by appling a resistance and a force
it important to get the highest resistance in the mittle
Can happen:
- to small nugget
- Gap, beacuse poor fitting
- Splash, to high current
- Burning outside
