In the process that designs LED drive circuit, need design personnel is particularly attentive, each original is deciding service life, the article explains the sticks a capacitance note in LED drive circuit.

 

Stick a capacitance full name to be called multilayer (laminose, fold a layer) piece capacitor of type pottery and porcelain, english abbreviate is MLCC. When MLCC is pounded by temperature, begin easily to produce crackle from solder end. Go up in this bit, small size capacitance is more opposite than large size capacitance for the meeting is a bit better, the capacitance heat conduction that its principle is large size did not reach whole electric capacity so quickly, capacitance is then noumenal the difference in temperature of differentia is big, expand so measurement is different, produce stress thereby. The thick glass when this truth is mixed is easier than thin glass crack is same. Additional, in the cooling process after MLCC has soldered, the coefficient of expansion of MLCC and PCB is different, produce stress then, bring about crackle. Want to avoid this problem, the need when circumfluence solder has solder goodly temperature curve. If need not circumfluence solder and with wave crest solder, so this kind of invalidation can increase greatly. MLCC should prevent the craft that solders with iron handiwork more. However the thing always is done not have so ideal. Iron handiwork solders sometimes inevitable also. E.g. , to the electronic manufacturer of treatment is being sent outside PCB, some product volumes are especially little, stick piece outside assist when manufacturer is not willing to receive this kind of sheet, can solder by hand only when; sample is produced, also be to solder by hand commonly do poorly done work over again of; special situation or when filling solder, must solder by hand when; repairman repairs capacitance, also be to solder by hand. Cannot avoid the ground to want to solder by hand when MLCC, be about to take welder seriously very much art.

 

 

Stick a capacitance

 

Well-known, of IC chip enclose the cent that sticks a type and biserial to insert type continuously. Think commonly: Sticking a type and biserial to insert the distinction of type continuously basically is bulk differ and solder the method is different, not big to systematic performance influence. Actually otherwise. On PCB each walk along a line to be put in aerial effect. Each component on PCB also is put in aerial effect, the electric part of component is larger, aerial effect is more powerful. So, same type chip, enclose the bigger than enclosing dimension aerial effect with small size to lose.

 

Same plant, use stick a component to insert component to pass EMC test more easily continuously than using biserial. In addition, aerial effect still follows the road of annulus of working electric current of every chip to concern. Want to weaken aerial effect, besides reduce enclose dimension, still should reduce size of road of annulus of working electric current as far as possible, reduce working frequency and Di/dt. The IC chip of advertent and newest model (especially odd piece) pin layout can discover: They abandoned mostly traditional pattern —— is left next horn are VCC for GND top right corner, and be in VCC and GND arrangement photograph ortho-position buy, it is to reduce size of road of annulus of working electric current.

 

It is IC chip not only, resistor, capacitance (BUZ60) is enclosed also concern with EMC. With 0805 enclose the EMC performance with contain better than 1206, with 0603 enclose the EMC performance with contain better than 0805 again. At present popular is on international 0603 enclose. The exterior that the spare parts is enclosed is directive of the place when showing actual part solder receives circuit board and the place that solder chooses. It is dinkum dimensional concept. The component that differs accordingly but common and same part is enclosed, akin component also can have different spare parts to enclose. Resemble resistor, the injection that has a tradition inserts type, volume of this kind of component is larger, circuit board must bore ability finds a place for component, after the bore that finish, insert component, cross stannic furnace or gush stannum again (also but hand solder) , cost is higher, newer design is to use the face with little bulk to stick chip component (SMD) this kind of component need not bore, the film that use steel creams stannum of half frit shape board, put SMD component again, can solder be on circuit board.

 

Above is the note that should notice to stick a capacitance in designing a process, such ability designs give the drive with long life, do not waste resource.